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Lotus seed starch holds vast potential for utilization across various industries, with its content and structure directly influencing the commercial value of lotus seeds. However, there has been limited information available on the molecular mechanisms underlying lotus seed starch biosynthesis. In this study, three starch branching enzyme homologs were identified in the lotus genome, designated as NnSBE1 to NnSBE3, which possess conserved CBM_48 and α_Aamy domains. Among them, NnSBE1 exhibited predominant expression, with abundant transcript levels observed in lotus seeds and flower-related organs. Expression of NnSBE1 remained consistently up-regulated in lotus cotyledons from 6 to 21 days after pollination. Additionally, a C2H2-type finger protein encoding gene, NnLOL1, co-expressed with NnSBE1 in lotus cotyledons. As a seed-predominantly expressed transcription factor, NnLOL1 was confirmed to activate NnSBE1 expression. Transient overexpression of NnSBE1 in lotus cotyledons resulted in a significant increase in both amylopectin and total starch content compared to the control. Furthermore, multiple variation sites within the NnSBE1 gene gave rise to diverse haplotypes between seed-lotus and other lotus varieties. These findings contribute to our understanding of the regulation mechanisms involved in lotus seed starch biosynthesis, offering valuable theoretical insights for the genetic improvement of lotus seed starch by molecular breeding strategies., Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Elsevier B.V. All rights reserved.) more...

This study explores the impact of juglone on cucumber (Cucumis sativus cv. Beith Alpha), scrutinizing its effects on seed germination, growth, and the polyphenol oxidase (PPO) enzyme's activity and gene expression. Employing concentrations ranging from 0.01 to 0.5 mM, we found juglone's effects to be concentration-dependent. At lower concentrations (0.01 and 0.1 mM), juglone promoted root and shoot growth along with germination, whereas higher concentrations (0.25 and 0.5 mM) exerted inhibitory effects, delineating a threshold for its allelopathic influence. Notably, PPO activity surged, especially at 0.5 mM in roots, hinting at oxidative stress involvement. Real-time PCR unveiled that juglone modulates PPO gene expression in cotyledons, peaking at 0.1 mM and diminishing at elevated levels. Correlation analyses elucidated a positive link between juglone-induced root growth and cotyledon PPO gene expression but a negative correlation with heightened root enzyme activity. Additionally, germination percentage inversely correlated with root PPO activity, while PPO activities positively associated with dopa and catechol substrates in both roots and cotyledons. Molecular docking studies revealed juglone's selective interactions with PPO's B chain, suggesting regulatory impacts. Protein interaction assessments highlighted juglone's influence on amino acid metabolism, and molecular dynamics indicated juglone's stronger, more stable binding to PPO, inferring potential alterations in enzyme function and stability. Conclusively, our findings elucidate juglone's dose-dependent physiological and biochemical shifts in cucumber plants, offering insights into its role in plant growth, stress response, and metabolic modulation., (© 2024 The Author(s). Physiologia Plantarum published by John Wiley & Sons Ltd on behalf of Scandinavian Plant Physiology Society.) more...

Fresh lotus seeds are gaining favor with consumers for their crunchy texture and natural sweetness. However, the intricacies of sugar accumulation in lotus seeds remain elusive, which greatly hinders the quality improvement of fresh lotus seeds. This study endeavors to elucidate this mechanism by identifying and characterizing the sucrose synthase (SUS) gene family in lotus. Comprising five distinct members, namely NnSUS1 to NnSUS5, each gene within this family features a C-terminal glycosyl transferase1 (GT1) domain. Among them, NnSUS1 is the predominately expressed gene, showing high transcript abundance in the floral organs and cotyledons. NnSUS1 was continuously up-regulated from 6 to 18 days after pollination (DAP) in lotus cotyledons. Furthermore, NnSUS1 demonstrates co-expression relationships with numerous genes involved in starch and sucrose metabolism. To investigate the function of NnSUS1, a transient overexpression system was established in lotus cotyledons, which confirmed the gene's contribution to sugar accumulation. Specifically, transient overexpression of NnSUS1 in seed cotyledons leads to a significant increase in the levels of total soluble sugar, including sucrose and fructose. These findings provide valuable theoretical insights for improving sugar content in lotus seeds through molecular breeding methods., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Masson SAS. All rights reserved.) more...

The plant-specific receptor-like cytoplasmic kinases (RLCKs) form a large, poorly characterized family. Members of the RLCK VI_A class of dicots have a unique characteristic: their activity is regulated by Rho-of-plants (ROP) GTPases. The biological function of one of these kinases was investigated using a T-DNA insertion mutant and RNA interference. Loss of RLCK VI_A2 function resulted in restricted cell expansion and seedling growth. Although these phenotypes could be rescued by exogenous gibberellin, the mutant did not exhibit lower levels of active gibberellins nor decreased gibberellin sensitivity. Transcriptome analysis confirmed that gibberellin is not the direct target of the kinase; its absence rather affected the metabolism and signalling of other hormones such as auxin. It is hypothesized that gibberellins and the RLCK VI_A2 kinase act in parallel to regulate cell expansion and plant growth. Gene expression studies also indicated that the kinase might have an overlapping role with the transcription factor circuit (PIF4-BZR1-ARF6) controlling skotomorphogenesis-related hypocotyl/cotyledon elongation. Furthermore, the transcriptomic changes revealed that the loss of RLCK VI_A2 function alters cellular processes that are associated with cell membranes, take place at the cell periphery or in the apoplast, and are related to cellular transport and/or cell wall reorganisation., Competing Interests: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results. more...

Transfer cells are characterized by an amplified plasma membrane area supported on a wall labyrinth composed of a uniform wall layer (UWL) from which wall ingrowth (WI) papillae arise. Adaxial epidermal cells of developing Vicia faba cotyledons, when placed in culture, undergo a rapid (hours) trans-differentiation to a functional epidermal transfer cell (ETC) phenotype. The trans-differentiation event is controlled by a signalling cascade comprising auxin, ethylene, apoplasmic reactive oxygen species (apoROS), and cytosolic Ca2+. Apoplasmic hydrogen peroxide (apoH2O2) was confirmed as the apoROS regulating UWL and WI papillae formation. Informed by an ETC-specific transcriptome, a pharmacological approach identified a temporally changing cohort of H2O2 biosynthetic enzymes. The cohort contained a respiratory burst oxidase homologue, polyamine oxidase, copper amine oxidase, and a suite of class III peroxidases. Collectively these generated two consecutive bursts in apoH2O2 production. Spatial organization of biosynthetic/catabolic enzymes was deduced from responses to pharmacologically blocking their activities on the cellular and subcellular distribution of apoH2O2. The findings were consistent with catalase activity constraining the apoH2O2 signal to the outer periclinal wall of the ETCs. Strategic positioning of class III peroxidases in this outer domain shaped subcellular apoH2O2 signatures that differed during assembly of the UWL and WI papillae., (© The Author(s) 2019. Published by Oxford University Press on behalf of the Society for Experimental Biology.) more...

The catalytic activity of mitogen-activated protein kinases (MAPKs) is dynamically modified in plants. Since MAPKs have been shown to play important roles in a wide range of signaling pathways, the ability to monitor MAPK activity in living plant cells would be valuable. Here, we report the development of a genetically encoded MAPK activity sensor for use in Arabidopsis thaliana. The sensor is composed of yellow and blue fluorescent proteins, a phosphopeptide binding domain, a MAPK substrate domain and a flexible linker. Using in vitro testing, we demonstrated that phosphorylation causes an increase in the Förster resonance energy transfer (FRET) efficiency of the sensor. The FRET efficiency can therefore serve as a readout of kinase activity. We also produced transgenic Arabidopsis lines expressing this sensor of MAPK activity (SOMA) and performed live-cell imaging experiments using detached cotyledons. Treatment with NaCl, the synthetic flagellin peptide flg22 and chitin all led to rapid gains in FRET efficiency. Control lines expressing a version of SOMA in which the phosphosite was mutated to an alanine did not show any substantial changes in FRET. We also expressed the sensor in a conditional loss-of-function double-mutant line for the Arabidopsis MAPK genes MPK3 and MPK6. These experiments demonstrated that MPK3/6 are necessary for the NaCl-induced FRET gain of the sensor, while other MAPKs are probably contributing to the chitin and flg22-induced increases in FRET. Taken together, our results suggest that SOMA is able to dynamically report MAPK activity in living plant cells., (© 2018 The Authors The Plant Journal © 2018 John Wiley & Sons Ltd.) more...

Fumarase (EC 4.2.1.2) is encoded in sunflower (Helianthus annuus L.) by two genes (FUM1 and FUM2) expressing correspondingly the mitochondrial and the cytosolic form. Both forms have been purified from sunflower cotyledons and characterized. Three quarters of fumarase activity is located in the mitochondrial and one quarter in the cytosolic fraction. The cytosolic form has lower pH optimum than the mitochondrial form, it possesses higher affinity to malate, activated by Mn 2+ and less efficiently by Mg 2+ while the mitochondrial form is activated only by Mg 2+ . It is proposed that the mitochondrial form is involved in the respiratory processes linked to the tricarboxylic acid cycle and the cytosolic form participates in the utilization of succinate produced in the glyoxylate cycle providing the flux to gluconeogenesis in germinating sunflower seeds., (Copyright © 2018 Elsevier Masson SAS. All rights reserved.) more...

Main Conclusion: Mitogen-activated protein kinases seem to mark genes which are set up to be activated in daughter cells and thus they may play a direct role in cellular patterning during embryogenesis. Embryonic patterning starts very early and after the first division of zygote different genes are expressed in apical and basal cells. However, there is an ongoing debate about the way these different transcription patterns are established during embryogenesis. The presented data indicate that mitogen-activated protein kinases (MAPKs) concentrate in the vicinity of chromosomes and form visible foci there. Cells in the apical and basal regions differ in number of foci observed during the metaphase which suggests that cellular patterning may be determined by activation of diverse MAPK-dependent genes. Different number of foci in each group of separating chromatids and the specified direction of these mitoses in apical-basal axis indicate that the unilateral auxin accumulation in a single cell may regulate the number of foci in each group of chromatids. Thus, we put forward a hypothesis that MAPKs localized in the vicinity of chromosomes during mitosis mark those genes which are set up to be activated in daughter cells after division. It implies that the chromosomal localization of MAPKs may be one of the mechanisms involved in establishment of cellular patterns in some plant species. more...

Premise of the Study: Tetraena simplex is an independently evolved C 4 species in the Zygophylloideae (Zygophyllaceae) and a characteristic forb of saline flats in hot and sandy desert habitats. During early ontogeny, the species had a morphological shift from planar cotyledons (dorsiventral symmetry) to terete, succulent leaves (radial symmetry). We tested whether this shift had a corresponding change in internal Kranz anatomy and tissue patterning., Methods: For a comprehensive characterization of C 4 photosynthesis across early ontogeny in T. simplex, structural and ultrastructural anatomical properties and localization patterns, activities, and immunoblotting of key C 4 photosynthetic enzymes were compared in mesophyll and bundle sheath tissues in cotyledons and leaves., Key Results: Cotyledons and leaves possessed different types of Kranz anatomy (atriplicoid type and a "Tetraena" variant of the kochioid type, respectively), reflecting the change in leaf morphology. In bundle sheath cells, key differences in ultrastructural features included increased organelle numbers and chloroplast thylakoid stacking. C 4 enzymes had strict tissue-specific localization patterns within bundle sheath and mesophyll cells in both cotyledons and leaves. The decarboxylase NAD-ME maintained the highest activity, increasing from cotyledons to leaves. This classified T. simplex as fully C 4 across ontogeny and a strictly NAD-ME biochemical subtype., Conclusions: Tetraena simplex cotyledons and leaves showed differences in Kranz type, with associated progression in ultrastructural features, and differing activities/expression levels of C 4 enzymes. Furthermore, leaves characterized a new "Tetraena" variation of the kochioid Kranz anatomy., (© 2018 Botanical Society of America.) more...

Rhamnose is required in Arabidopsis thaliana for synthesizing pectic polysaccharides and glycosylating flavonols. RHAMNOSE BIOSYNTHESIS1 (RHM1) encodes a UDP-l-rhamnose synthase, and rhm1 mutants exhibit many developmental defects, including short root hairs, hyponastic cotyledons, and left-handed helically twisted petals and roots. It has been proposed that the hyponastic cotyledons observed in rhm1 mutants are a consequence of abnormal flavonol glycosylation, while the root hair defect is flavonol-independent. We have recently shown that the helical twisting of rhm1 petals results from decreased levels of rhamnose-containing cell wall polymers. In this study, we found that flavonols indirectly modify the rhm1 helical petal phenotype by altering rhamnose flux to the cell wall. Given this finding, we further investigated the relationship between flavonols and the cell wall in rhm1 cotyledons. We show that decreased flavonol rhamnosylation is not responsible for the cotyledon phenotype of rhm1 mutants. Instead, blocking flavonol synthesis or rhamnosylation can suppress rhm1 defects by diverting UDP-l-rhamnose to the synthesis of cell wall polysaccharides. Therefore, rhamnose is required in the cell wall for normal expansion of cotyledon epidermal cells. Our findings suggest a broad role for rhamnose-containing cell wall polysaccharides in the morphogenesis of epidermal cells., (© 2018 The Authors The Plant Journal © 2018 John Wiley & Sons Ltd.) more...

Chinese chestnut (Castanea mollissima Blume) is native to China and distributes widely in arid and semi-arid mountain area with barren soil. As a perennial crop, chestnut is an alternative food source and acts as an important commercial nut tree in China. Starch is the major metabolite in nuts, accounting for 46 ~ 64% of the chestnut dry weight. The accumulation of total starch and amylopectin showed a similar increasing trend during the development of nut. Amylopectin contributed up to 76% of the total starch content at 80 days after pollination (DAP). The increase of total starch mainly results from amylopectin synthesis. Among genes associated with starch biosynthesis, CmSBEs (starch branching enzyme) showed significant increase during nut development. Two starch branching enzyme isoforms, CmSBE I and CmSBE II, were identified from chestnut cotyledon using zymogram analysis. CmSBE I and CmSBE II showed similar patterns of expression during nut development. The accumulations of CmSBE transcripts and proteins in developing cotyledons were characterized. The expressions of two CmSBE genes increased from 64 DAP and reached the highest levels at 77 DAP, and SBE activity reached its peak at 74 DAP. These results suggested that the CmSBE enzymes mainly contributed to amylopectin synthesis and influenced the amylopectin content in the developing cotyledon, which would be beneficial to chestnut germplasm selection and breeding. more...

Acyltransferases are key contributors to triacylglycerol (TAG) synthesis and, thus, are of great importance for seed oil quality. The effects of increased or decreased expression of ACYL-COENZYME A:DIACYLGLYCEROL ACYLTRANSFERASE1 ( DGAT1 ) or PHOSPHOLIPID:DIACYLGLYCEROL ACYLTRANSFERASE ( PDAT ) on seed lipid composition were assessed in several Camelina sativa lines. Furthermore, in vitro assays of acyltransferases in microsomal fractions prepared from developing seeds of some of these lines were performed. Decreased expression of DGAT1 led to an increased percentage of 18:3 n -3 without any change in total lipid content of the seed. The tri-18:3 TAG increase occurred predominantly in the cotyledon, as determined with matrix-assisted laser desorption/ionization-mass spectrometry, whereas species with two 18:3 n -3 acyl groups were elevated in both cotyledon and embryonal axis. PDAT overexpression led to a relative increase of 18:2 n -6 at the expense of 18:3 n -3, also without affecting the total lipid content. Differential distributions of TAG species also were observed in different parts of the seed. The microsomal assays revealed that C. sativa seeds have very high activity of diacylglycerol-phosphatidylcholine interconversion. The combination of analytical and biochemical data suggests that the higher 18:2 n -6 content in the seed oil of the PDAT overexpressors is due to the channeling of fatty acids from phosphatidylcholine into TAG before being desaturated to 18:3 n -3, caused by the high activity of PDAT in general and by PDAT specificity for 18:2 n -6. The higher levels of 18:3 n -3 in DGAT1 -silencing lines are likely due to the compensatory activity of a TAG-synthesizing enzyme with specificity for this acyl group and more desaturation of acyl groups occurring on phosphatidylcholine., (© 2017 American Society of Plant Biologists. All Rights Reserved.) more...

Proanthocyanidins (PAs) are a major group of flavonoids synthesized via the phenylpropanoid biosynthesis pathway, however the pathway has not been fully characterized in buckwheat. Anthocyanidin reductase (ANR) and leucoanthocyanidin reductase (LAR) are involved in the last steps of PA biosynthesis. To isolate the genes for these enzymes from buckwheat we performed PCR using degenerate primers and obtained cDNAs of ANR and LAR, which we designated FeANR and FeLAR1. A search for homologs in a buckwheat genome database with both sequences returned two more LAR sequences, designated FeLAR2 and FeLAR3. Linkage analysis with an F 2 segregating population indicated that the three LAR loci were not genetically linked. We detected high levels of PAs in roots and cotyledons of buckwheat seedlings and in buds and flowers of mature plants. FeANR and FeLAR1-3 were expressed in most organs but had different expression patterns. Our findings would be useful for breeding and further analysis of PA synthesis and its regulation in buckwheat., (Copyright © 2016 Elsevier GmbH. All rights reserved.) more...

Key Message: Arabidopsis CK2 α4 subunit regulates the primary root and hypocotyl elongation, lateral root formation, cotyledon expansion, rosette leaf initiation and growth, flowering, and anthocyanin biosynthesis. Casein kinase 2 (CK2) is a conserved tetrameric kinase composed of two α and two β subunits. The inhibition of CK2 activity usually results in severe developmental deficiency. Four genes (CKA1-CKA4) encode CK2 α subunit in Arabidopsis. Single mutations of CKA1, CKA2, and CKA3 do not affect the normal growth of Arabidopsis, while the cka1 cka2 cka3 triple mutants are defective in cotyledon and hypocotyl growth, lateral root development, and flowering. The inhibition of CKA4 expression in cka1 cka2 cka3 background further reduces the number of lateral roots and delays the flowering time. Here, we report the characterization of a novel knockout mutant of CKA4, which exhibits various developmental defects including reduced primary root and hypocotyl elongation, increased lateral root density, delayed cotyledon expansion, retarded rosette leaf initiation and growth, and late flowering. The examination of the cellular basis for abnormal root development of this mutant revealed reduced root meristem cells with enhanced RETINOBLASTOMA-RELATED (RBR) expression that promotes cell differentiation in root meristem. Moreover, this cka4-2 mutant accumulates higher anthocyanin in the aerial part and shows an increased expression of anthocyanin biosynthetic genes, suggesting a novel role of CK2 in modulating anthocyanin biosynthesis. In addition, the complementation test using primary root elongation assay as a sample confirms that the changed phenotypes of this cka4-2 mutant are due to the lack of CKA4. Taken together, this study reveals an essential role of CK2 α4 subunit in multiple developmental processes in Arabidopsis. more...

This study is aimed to investigate the activity of urease (EC 3.5.1.5, urea amidohydrolase) that catalyzes the hydrolysis of urea in 5-day-old Cucurbita pepo cotyledons subjected to various concentrations of different growth regulators. The treatment of C. pepo cotyledons with different concentrations (100-600 μmol) of different auxins [indole-3-acetic acid (IAA), indole butyric acid (IBA), indole propionic acid (IPA) and naphthalene acetic acid (NAA)]; or with different concentrations (100-300 μmol) of different cytokinins [kinetin, zeatin and benzyladenine (6-BA)] resulted in a significant increase of urease activity, compared to control. The optimal effects were recorded for each of 500 μmol of IAA and 300 μmol of zeatin treatments. A gradual increase in urease activity was detected in cotyledons treated with various concentrations (0.2-1.0 mM) of 28-homobrassinolide (HBL), in relative to control. A substantial increase in urease activity was observed in cotyledons subjected to different concentrations of triazole (10-60 mg L(-1)), containing either triadimefon (TDM) or hexaconazole (HEX), compared to control. The combination of 300 μmol zeatin with any of protein inhibitors, namely 5-fluorouridine (FUrd), cordycepin and α-amanitin, resulted in the alleviation of their inhibitory effect on the urease activity. more...

Legumains are cysteine proteases related to plant development, protein degradation, programmed cell death, and defense against pathogens. In this study, we have identified and characterized three legumains encoded by Theobroma cacao genome through in silico analyses, three-dimensional modeling, genetic expression pattern in different tissues and as a response to the inoculation of Moniliophthora perniciosa fungus. The three proteins were named TcLEG3, TcLEG6, and TcLEG9. Histidine and cysteine residue which are part of the catalytic site were conserved among the proteins, and they remained parallel in the loop region in the 3D modeling. Three-dimensional modeling showed that the propeptide, which is located in the terminal C region of legumains blocks the catalytic cleft. Comparing dendrogram data with the relative expression analysis, indicated that TcLEG3 is related to the seed legumain group, TcLEG6 is related with the group of embryogenesis activities, and protein TcLEG9, with processes regarding the vegetative group. Furthermore, the expression analyses proposes a significant role for the three legumains during the development of Theobroma cacao and in its interaction with M. perniciosa., (Copyright © 2015 Universidade Estadual de Santa Cruz, CNPJ: 40738999/0001-95. Published by Elsevier Masson SAS.. All rights reserved.) more...

Auxin is a major growth hormone in plants and the first plant hormone to be discovered and studied. Active research over >60 years has shed light on many of the molecular mechanisms of its action including transport, perception, signal transduction, and a variety of biosynthetic pathways in various species, tissues, and developmental stages. The complexity and redundancy of the auxin biosynthetic network and enzymes involved raises the question of how such a system, producing such a potent agent as auxin, can be appropriately controlled at all. Here it is shown that maize auxin biosynthesis takes place in microsomal as well as cytosolic cellular fractions from maize seedlings. Most interestingly, a set of enzymes shown to be involved in auxin biosynthesis via their activity and/or mutant phenotypes and catalysing adjacent steps in YUCCA-dependent biosynthesis are localized to the endoplasmic reticulum (ER). Positioning of auxin biosynthetic enzymes at the ER could be necessary to bring auxin biosynthesis in closer proximity to ER-localized factors for transport, conjugation, and signalling, and allow for an additional level of regulation by subcellular compartmentation of auxin action. Furthermore, it might provide a link to ethylene action and be a factor in hormonal cross-talk as all five ethylene receptors are ER localized., (© The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com.) more...

Isoflavone conjugates [7-O-β-D-glucosides and 7-O-(6″-malonyl-β-D-glucosides) of daidzein and genistein] accumulate in soybean roots and serve as the stored precursors of isoflavones (aglycons), which play very important roles in the rhizobia-mediated nodulation of this plant. Thus far, the isoflavone 7-O-glucosyltransferase (GmIF7GT or GmUGT1) has been biochemically characterized and is believed to be involved in isoflavone conjugate biosynthesis. The soybean genome encodes many other glycosyltransferase homologs (GmUGTs) that are related to GmUGT1; however, their catalytic properties, substrate specificities, and role(s) in isoflavone conjugation are unknown. In this study, nine different GmUGT1-related GmUGT cDNAs were isolated; six of these cDNAs belonged to two distinct phylogenetic subgroups (A and B), and these six were functionally characterized. The results showed that GmUGT4, a representative of subgroup A, encoded a UGT that was highly specific for isoflavones showing kcat and kcat/Km values for daidzein of 5.89 ± 0.65 s(-1) and 2.91 × 10(5) s(-1)M(-1), respectively. Moreover, GmUGT4 was expressed in the roots (mainly in lateral roots) of the 7-day-old seedlings and seeds, both of which contained abundant amounts of isoflavone conjugates. By contrast, GmUGT1 and GmUGT7, which were subgroup B members, encoded enzymes with broad glucosyl-acceptor specificities and were mainly expressed in the aerial portions (cotyledons and hypocotyls) of the seedlings. In the present study, we proposed that the role of isoflavone glucosylation in a soybean plant is assigned to different GmUGT members in an organ/tissue-dependent manner. We also established the functional importance of GmUGT4 in the biosynthesis of isoflavone conjugates in lateral roots that make a major contribution to overall N2 fixation., (© The Author 2015. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oup.com.) more...

Anoxia tolerance in plants is distinguished by direction of the sparse supply of energy to processes crucial to cell maintenance and sometimes to growth, as in rice seedlings. In anoxic rice coleoptiles energy is used to synthesise proteins, take up K(+) , synthesise cell walls and lipids, and in cell maintenance. Maintenance of electrochemical H(+) gradients across the tonoplast and plasma membrane is crucial for solute compartmentation and thus survival. These gradients sustain some H(+) -solute cotransport and regulate cytoplasmic pH. Pyrophosphate (PPi ), the alternative energy donor to ATP, allows direction of energy to the vacuolar H(+) -PPi ase, sustaining H(+) gradients across the tonoplast. When energy production is critically low, operation of a biochemical pHstat allows H(+) -solute cotransport across plasma membranes to continue for at least for 18 h. In active (e.g. growing) cells, PPi produced during substantial polymer synthesis allows conversion of PPi to ATP by PPi -phosphofructokinase (PFK). In quiescent cells with little polymer synthesis and associated PPi formation, the PPi required by the vacuolar H(+) -PPi ase and UDPG pyrophosphorylase involved in sucrose mobilisation via sucrose synthase might be produced by conversion of ATP to PPi through reversible glycolytic enzymes, presumably pyruvate orthophosphate dikinase. These hypotheses need testing with species characterised by contrasting anoxia tolerance., (© 2014 The Authors. New Phytologist © 2014 New Phytologist Trust.) more...

Chloroplasts perform many essential metabolic functions and their proper development is critically important in embryogenesis. However, little is known about how chloroplasts function in embryogenesis and more relevant components need to be characterized. In this study, we show that Arabidopsis Ribonuclease J (RNase J) is required for chloroplast and embryo development. Mutation of AtRNJ led to albino ovules containing aborted embryos; the morphological development of rnj embryos was disturbed after the globular stage. Observation of ultrastructures indicated that these aborted embryos may result from impaired chloroplast development. Furthermore, by analyzing the molecular markers of cell fate decisions (STM, FIL, ML1, SCR, and WOX5) in rnj embryos, we found that this impairment of chloroplast development may lead to aberrant embryo patterning along the apical-basal axis, indicating that AtRNJ is important in initiating and maintaining the organization of shoot apical meristems (SAMs), cotyledons, and hypocotyls. Moreover, the transport and response of auxin in rnj embryos was found to be disrupted, suggesting that AtRNJ may be involved in auxin-mediated pathways during embryogenesis. Therefore, we speculate that RNJ plays a vital role in embryo morphogenesis and apical-basal pattern formation by regulating chloroplast development., (© The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology.) more...

The short-day plant pharbitis (also called Japanese morning glory), Ipomoea nil (formerly Pharbitis nil), was induced to flower by poor-nutrition stress. This stress-induced flowering was inhibited by aminooxyacetic acid (AOA), which is a known inhibitor of phenylalanine ammonia-lyase (PAL) and the synthesis of indole-3-acetic acid (IAA) and 1-aminocycropropane-1-carboxylic acid (ACC) and thus regulates endogenous levels of salicylic acid (SA), IAA and polyamine (PA). Stress treatment increased PAL activity in cotyledons, and AOA suppressed this increase. The observed PAL activity and flowering response correlate positively, indicating that AOA functions as a PAL inhibitor. The inhibition of stress-induced flowering by AOA was also overcome by IAA. An antiauxin, 4-chlorophenoxy isobutyric acid, inhibited stress-induced flowering. Both SA and IAA promoted flowering induced by stress. PA also promoted flowering, and the effective PA was found to be putrescine (Put). These results suggest that all of the pathways leading to the synthesis of SA, IAA and Put are responsive to the flowering inhibition by AOA and that these endogenous factors may be involved in the regulation of stress-induced flowering. However, as none of them induced flowering under non-stress conditions, they may function cooperatively to promote flowering., (Copyright © 2014 Elsevier GmbH. All rights reserved.) more...

C-Glycosides are characterized by their C-C bonds in which the anomeric carbon of the sugar moieties is directly bound to the carbon atom of aglycon. C-Glycosides are remarkably stable, as their C-C bonds are resistant to glycosidase or acid hydrolysis. A variety of plant species are known to accumulate C-glycosylflavonoids; however, the genes encoding for enzymes that catalyze C-glycosylation of flavonoids have been identified only from Oryza sativa (rice) and Zea mays (maize), and have not been identified from dicot plants. In this study, we identified the C-glucosyltransferase gene from the dicot plant Fagopyrum esculentum M. (buckwheat). We purified two isozymes from buckwheat seedlings that catalyze C-glucosylation of 2-hydroxyflavanones, which are expressed specifically in the cotyledon during seed germination. Following purification we isolated the cDNA corresponding to each isozyme [FeCGTa (UGT708C1) and FeCGTb (UGT708C2)]. When expressed in Escherichia coli, both proteins demonstrated C-glucosylation activity towards 2-hydroxyflavanones, dihydrochalcone, trihydroxyacetophenones and other related compounds with chemical structures similar to 2',4',6'-trihydroxyacetophenone. Molecular phylogenetic analysis of plant glycosyltransferases shows that flavonoid C-glycosyltransferases form a different clade with other functionally analyzed plant glycosyltransferases., (© 2014 The Authors The Plant Journal © 2014 John Wiley & Sons Ltd.) more...

Chlorophylls, the most abundant pigments in the photosynthetic apparatus, are constantly turned over as a result of the degradation and replacement of the damage-prone reaction center D1 protein of photosystem II. Results from isotope labeling experiments suggest that chlorophylls are recycled by reutilization of chlorophyllide and phytol, but the underlying mechanism is unclear. In this study, by characterization of a heat-sensitive Arabidopsis mutant we provide evidence of a salvage pathway for chlorophyllide a. A missense mutation in CHLOROPHYLL SYNTHASE (CHLG) was identified and confirmed to be responsible for a light-dependent, heat-induced cotyledon bleaching phenotype. Following heat treatment, mutant (chlg-1) but not wild-type seedlings accumulated a substantial level of chlorophyllide a, which resulted in a surge of phototoxic singlet oxygen. Immunoblot analysis suggested that the mutation destabilized the chlorophyll synthase proteins and caused a conditional blockage of esterification of chlorophyllide a after heat stress. Accumulation of chlorophyllide a after heat treatment occurred during recovery in the dark in the light-grown but not the etiolated seedlings, suggesting that the accumulated chlorophyllides were not derived from de novo biosynthesis but from de-esterification of the existing chlorophylls. Further analysis of the triple mutant harboring the CHLG mutant allele and null mutations of CHLOROPHYLLASE1 (CLH1) and CLH2 indicated that the known chlorophyllases are not responsible for the accumulation of chlorophyllide a in chlg-1. Taken together, our results show that chlorophyll synthase acts in a salvage pathway for chlorophyll biosynthesis by re-esterifying the chlorophyllide a produced during chlorophyll turnover., (© 2014 The Authors The Plant Journal © 2014 John Wiley & Sons Ltd.) more...

Momordica charantia is often called bitter melon, bitter gourd or bitter squash because its fruit has a bitter taste. The fruit has been widely used as vegetable and herbal medicine. Alpha-eleostearic acid is the major fatty acid in the seeds, but little is known about its biosynthesis. As an initial step towards understanding the biochemical mechanism of fatty acid accumulation in bitter melon seeds, this study focused on a soluble phosphatidic acid phosphatase (PAP, 3-sn-phosphatidate phosphohydrolase, EC 3.1.3.4) that hydrolyzes the phosphomonoester bond in phosphatidate yielding diacylglycerol and P(i). PAPs are typically categorized into two subfamilies: Mg(2+)-dependent soluble PAP and Mg(2+)-independent membrane-associated PAP. We report here the partial purification and characterization of an Mg(2+)-independent PAP activity from developing cotyledons of bitter melon. PAP protein was partially purified by successive centrifugation and UNOsphere Q and S columns from the soluble extract. PAP activity was optimized at pH 6.5 and 53-60 °C and unaffected by up to 0.3 mM MgCl2. The K(m) and Vmax values for dioleoyl-phosphatidic acid were 595.4 µM and 104.9 ηkat/mg of protein, respectively. PAP activity was inhibited by NaF, Na(3)VO(4), Triton X-100, FeSO4 and CuSO4, but stimulated by MnSO4, ZnSO4 and Co(NO3)2. In-gel activity assay and mass spectrometry showed that PAP activity was copurified with a number of other proteins. This study suggests that PAP protein is probably associated with other proteins in bitter melon seeds and that a new class of PAP exists as a soluble and Mg(2+)-independent enzyme in plants. more...

Purine nucleotides can be fully catabolized by plants to recycle nutrients. We have isolated a urate oxidase (uox) mutant of Arabidopsis thaliana that accumulates uric acid in all tissues, especially in the developing embryo. The mutant displays a reduced germination rate and is unable to establish autotrophic growth due to severe inhibition of cotyledon development and nutrient mobilization from the lipid reserves in the cotyledons. The uox mutant phenotype is suppressed in a xanthine dehydrogenase (xdh) uox double mutant, demonstrating that the underlying cause is not the defective purine base catabolism, or the lack of UOX per se, but the elevated uric acid concentration in the embryo. Remarkably, xanthine accumulates to similar levels in the xdh mutant without toxicity. This is paralleled in humans, where hyperuricemia is associated with many diseases whereas xanthinuria is asymptomatic. Searching for the molecular cause of uric acid toxicity, we discovered a local defect of peroxisomes (glyoxysomes) mostly confined to the cotyledons of the mature embryos, which resulted in the accumulation of free fatty acids in dry seeds. The peroxisomal defect explains the developmental phenotypes of the uox mutant, drawing a novel link between uric acid and peroxisome function, which may be relevant beyond plants., (© 2014 American Society of Plant Biologists. All rights reserved.) more...

The role of the ubiquitin (Ub)-proteasome pathway and some endo- and aminopeptidases (EPs and APs, respectively) was studied in cotyledons of germinating bean seeds (Phaseolus vulgaris L.). The Ub system appeared to be important both in the early (3 days) and late (9 days) phases of germination. In the presence of copper, an increase in protein carbonylation and a decrease in reduced -SH pool occurred, indicating protein damage. This was associated with an enhancement in accumulation of malondialdehyde, a major product of lipid peroxidation, and an increase in content of hydrogen peroxide (H2O2), showing oxidative stress generation. Moreover, copper induced inactivation of the Ub-proteasome (EC 3.4.25) pathway and inhibition of leucine and proline aminopeptidase activities (EC 3.4.11.1 and EC 3.4.11.5, respectively), thus limiting their role in modulating essential metabolic processes, such as the removal of regulatory and oxidatively-damaged proteins. By contrast, total trypsin and chymotrypsin-like activities (EC 3.4.21.4 and EC 3.4.21.1, respectively) increased after copper exposure, in parallel with a decrease in their inhibitor capacities (i.e. trypsin inhibitor and chymotrypsin inhibitor activity), suggesting that these endoproteases are part of the protective mechanisms against copper stress., (Copyright © 2014 Elsevier Masson SAS. All rights reserved.) more...

Fenugreek (Trigonella foenum-graecum) seeds do not contain starch as carbohydrate reserve. Synthesis of starch is initiated after germination. A β-amylase from ungerminated fenugreek seeds was purified to apparent electrophoretic homogeneity. The enzyme was purified 210 fold with specific activity of 732.59 units/mg. Mr of the denatured enzyme as determined from SDS-PAGE was 58 kD while that of native enzyme calculated from size exclusion chromatography was 56 kD. Furthermore, its identity was confirmed to be β-amylase from MALDI-TOF analysis. The optimum pH and temperature was found to be 5.0 and 50°C, respectively. Starch was hydrolyzed at highest rate and enzyme showed a Km of 1.58 mg/mL with it. Antibodies against purified Fenugreek β-amylase were generated in rabbits. These antibodies were used for localization of enzyme in the cotyledon during different stages of germination using fluorescence and confocal microscopy. Fenugreek β-amylase was found to be the major starch degrading enzyme depending on the high amount of enzyme present as compared to α-amylase and also its localization at the periphery of amyloplasts. A new finding in terms of its association with protophloem was observed. Thus, this enzyme appears to be important for germination of seeds. more...

Indole-3-acetic acid (IAA), an auxin plant hormone, is biosynthesized from tryptophan. The indole-3-pyruvic acid (IPyA) pathway, involving the tryptophan aminotransferase TAA1 and YUCCA (YUC) enzymes, was recently found to be a major IAA biosynthetic pathway in Arabidopsis. TAA1 catalyzes the conversion of tryptophan to IPyA, and YUC produces IAA from IPyA. Using a chemical biology approach with maize coleoptiles, we identified 5-(4-chlorophenyl)-4H-1,2,4-triazole-3-thiol (yucasin) as a potent inhibitor of IAA biosynthesis in YUC-expressing coleoptile tips. Enzymatic analysis of recombinant AtYUC1-His suggested that yucasin strongly inhibited YUC1-His activity against the substrate IPyA in a competitive manner. Phenotypic analysis of Arabidopsis YUC1 over-expression lines (35S::YUC1) demonstrated that yucasin acts in IAA biosynthesis catalyzed by YUC. In addition, 35S::YUC1 seedlings showed resistance to yucasin in terms of root growth. A loss-of-function mutant of TAA1, sav3-2, was hypersensitive to yucasin in terms of root growth and hypocotyl elongation of etiolated seedlings. Yucasin combined with the TAA1 inhibitor l-kynurenine acted additively in Arabidopsis seedlings, producing a phenotype similar to yucasin-treated sav3-2 seedlings, indicating the importance of IAA biosynthesis via the IPyA pathway in root growth and leaf vascular development. The present study showed that yucasin is a potent inhibitor of YUC enzymes that offers an effective tool for analyzing the contribution of IAA biosynthesis via the IPyA pathway to plant development and physiological processes., (© 2013 The Authors The Plant Journal © 2013 John Wiley & Sons Ltd.) more...

The major seed storage reserves in oilseeds are accumulated in protein bodies and oil bodies, and serve as an energy, carbon, and nitrogen source during germination. Here, the spatio-temporal relationships between protein bodies and several key enzymes (phospholipase A, lipase, and lipoxygenase) involved in storage lipid mobilization in cotyledon cells was analysed during in vitro seed germination. Enzyme activities were assayed in-gel and their cellular localization were determined using microscopy techniques. At seed maturity, phospholipase A and triacylglycerol lipase activities were found exclusively in protein bodies. However, after seed imbibition, these activities were shifted to the cytoplasm and the surface of the oil bodies. The activity of neutral lipases was detected by using α-naphthyl palmitate and it was associated mainly with protein bodies during the whole course of germination. This pattern of distribution was highly similar to the localization of neutral lipids, which progressively appeared in protein bodies. Lipoxygenase activity was found in both the protein bodies and on the surface of the oil bodies during the initial phase of seed germination. The association of lipoxygenase with oil bodies was temporally correlated with the appearance of phospholipase A and lipase activities on the surface of oil bodies. It is concluded that protein bodies not only serve as simple storage structures, but are also dynamic and multifunctional organelles directly involved in storage lipid mobilization during olive seed germination. more...

Background: Oilseed germination is characterized by the degradation of storage lipids. It may proceed either via the direct action of a triacylglycerol lipase, or in certain plant species via a specific lipid body 13-lipoxygenase. For the involvement of a lipoxygenase previous results suggested that the hydroxy- or oxo-group that is being introduced into the fatty acid backbone by this lipoxygenase forms a barrier to continuous β-oxidation., Results: This study shows however that a complete degradation of oxygenated fatty acids is possible by isolated cucumber and sunflower glyoxysomes. Interestingly, degradation is accompanied by the formation of saturated short chain acyl-CoAs with chain length between 4 and 12 carbon atoms lacking the hydroxy- or oxo-diene system of the oxygenated fatty acid substrate. The presence of these CoA esters suggests the involvement of a specific reduction of the diene system at a chain length of 12 carbon atoms including conversion of the hydroxy-group at C7., Conclusions: To our knowledge this metabolic pathway has not been described for the degradation of polyunsaturated fatty acids so far. It may represent a new principle to degrade oxygenated fatty acid derivatives formed by lipoxygenases or chemical oxidation initiated by reactive oxygen species. more...

Among starchy seeds, rice has the unique capacity to germinate successfully under complete anaerobiosis. In this conditions, starch degradation is supported by a complete set of starch-degrading enzymes that are absent or inactive in cereals except rice. A characterization of carbohydrate metabolism and starch-degrading enzyme activity across twenty-nine genotypes of Oryza sativa L. is presented here. The zymogram of amylolytic activities present in rice embryos and endosperms under anaerobic conditions seven days after sowing (DAS) revealed marked differences among cultivars. Coleoptile elongation was positively correlated with total amylolytic activities and α-amylase activity in embryos, and negatively correlated with α-amylase activity in endosperm. Moreover, carbohydrate content in embryos was found to be positively correlated with total amylolytic activities under anaerobic conditions, while a negative relationship was recorded in the endosperm. Carbohydrate status in rice seedlings has a primary importance in sustaining coleoptile elongation towards the surface. The relationship between carbohydrate level in embryo and anoxic germination, as well as with total amylolytic activities present in rice embryo under anaerobic condition 7 DAS, is consistent with the role of sugar metabolism to support rice germination under oxygen-deprived environment. more...

Sorbitol is the primary photosynthate and translocated carbohydrate in fruit trees of the Rosaceae family. NAD(+)-dependent sorbitol dehydrogenase (NAD-SDH, EC 1.1.1.14), which mainly catalyzes the oxidation of sorbitol to fructose, plays a key role in regulating sink strength in apple. In this study, we found that apple NAD-SDH was ubiquitously distributed in epidermis, parenchyma, and vascular bundle in developing cotyledon. NAD-SDH was localized in the cytosol, the membranes of endoplasmic reticulum and vesicles, and the vacuolar lumen in the cotyledon at the middle stage of seed development. In contrast, NAD-SDH was mainly distributed in the protein storage vacuoles in cotyledon at the late stage of seed development. Sequence analysis revealed there is a putative signal peptide (SP), also being predicated to be a transmembrane domain, in the middle of proteins of apple NAD-SDH isoforms. To investigate whether the putative internal SP functions in the vacuolar targeting of NAD-SDH, we analyzed the localization of the SP-deletion mutants of MdSDH5 and MdSDH6 (two NAD-SDH isoforms in apple) by the transient expression system in Arabidopsis protoplasts. MdSDH5 and MdSDH6 were not localized in the vacuoles after their SPs were deleted, suggesting the internal SP functions in the vacuolar targeting of apple NAD-SDH., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.) more...

Background: As a by product of higher value cotton fibre, cotton seed has been increasingly recognised to have excellent potential as a source of additional food, feed, biofuel stock and even a renewable platform for the production of many diverse biological molecules for agriculture and industrial enterprises. The large size difference between cotyledon and embryo axis that make up a cotton seed results in the under-representation of embryo axis gene transcript levels in whole seed embryo samples. Therefore, the determination of gene transcript levels in the cotyledons and embryo axes separately should lead to a better understanding of metabolism in these two developmentally diverse tissues., Results: A comparative study of transcriptome changes between cotton developing cotyledon and embryo axis has been carried out. 17,384 unigenes (20.74% of all the unigenes) were differentially expressed in the two adjacent embryo tissues, and among them, 7,727 unigenes (44.45%) were down-regulated and 9,657 unigenes (55.55%) were up-regulated in cotyledon., Conclusions: Our study has provided a comprehensive dataset that documents the dynamics of the transcriptome at the mid-maturity of cotton seed development and in discrete seed tissues, including embryo axis and cotyledon tissues. The results showed that cotton seed is subject to many transcriptome variations in these two tissue types and the differential gene expression between cotton embryo axis and cotyledon uncovered in our study should provide an important starting point for understanding how gene activity is coordinated during seed development to make a seed. Further, the identification of genes involved in rapid metabolite accumulation stage of seed development will extend our understanding of the complex molecular and cellular events in these developmental processes and provide a foundation for future studies on the metabolism, embryo differentiation of cotton and other dicot oilseed crops. more...

Glycosylation is an important post-translational modification involved in the modulation of a wide variety of cellular processes. Because glycosydases are central, the aim of this study was to investigate the glycosyl activity present in the cotyledons of the seeds of an important crop legume, Lupinus albus, as well as potential natural substrates of the detected enzymes. The glycosyl activity detected in the cotyledons beginning at seed imbibition and continuing until 9 days after, was due to a β-N-acetylhexosaminidase (β-NAHase), which was molecularly and biochemically characterized after purification. Two isoenzymes with molecular masses of 64 and 61 kDa were detected, each having five isoenzymes with pIs 5.3-5.6. The 64 and 61 kDa isoenzymes had the same protein core showing different degrees of glycosylation. The N-terminal sequence of the enzyme protein core was determined [VDSEDLI(EN)AFKIYVEDDNEHLQGSVD] and to our knowledge, is the first reported protein sequence from a plant β-NAHase. L. albus β-NAHase had Km values of 2.59 mM and 2.94 mM and V values of 18.40 μM min(-1) and 2.73 μM min(-1), for pNP-GlcNAc and pNP-GalNAc, an optimum pH of 5.0 and 4.0 and temperature of 50 °C and 60 °C were detected toward pNP-GlcNAc and pNP-GalNAc. In the presence of AgNO3, CoCl2, CuSO4, FeCl3, CdCl2 and ZnCl2 the enzymatic activity decreased more than 50%, and when in the presence of sugars, an activity reduction of no more than 25% was observed. A physiological role for β-NAHase in L. albus storage protein mobilization was investigated. β-NAHase has already been implicated in several biological processes, namely in glycoprotein processing during seed germination and seedling growth. However, the natural substrates used by this enzyme are not yet completely clarified. By gathering in vivo and in vitro data for β-NAHase activity together with globulin degradation, we suggest that L. albus β-NAHase is involved in the mobilization of storage protein degradation, with α-conglutin being a potential natural substrate for this enzyme., (Copyright © 2013 Elsevier GmbH. All rights reserved.) more...

Plants are proven effective bioreactors for the production of heterologous proteins including those desired by the biopharmaceutical industry. However, the potential of plants as bioreactors is limited by the availability of characterized plant promoters that can drive target gene expression in relatively distant plant species. Seeds are ideal for protein storage because seed proteins can be kept stably for several months. Hence, a strong promoter that can direct the expression and accumulation of target proteins within seeds represents a powerful tool in plant biotechnology. Toward this end, an effort was made to identify such a promoter from Vigna radiata (mung bean) to drive expression in dicot seeds. A 784-bp 5'-flanking sequence of the gene encoding the 8S globulin α' subunit (8SGα') of the V. radiata seed storage protein was isolated by genome walking. When the 5'-flanking region was analyzed with bioinformatics tools, numerous putative cis-elements were identified. The Green Fluorescent Protein (GFP) regulated by this promoter was observed to be transiently expressed in protoplasts derived from V. radiata cotyledons. Finally, transgenic Arabidopsis plants expressing the β-glucuronidase (GUS) reporter gene driven from the 8S globulin α' promoter showed strong GUS expression in transgenic embryos in both histochemical and quantitative GUS assays, confirming high expression within seeds. Therefore, the V. radiata 8S α' promoter has shown potential in directing expression in seeds for bioreactor applications. more...

Plant receptor-like protein kinases are thought to be involved in various cellular processes mediated by signal transduction pathways. There are about 45 lectin receptor kinases in Arabidopsis, but only a few have been studied. Here, we investigated the effect of the disruption and overexpression of a plasma membrane-localized L-type lectin-like protein kinase 1, AtLPK1 (At4g02410), on plant responses to abiotic and biotic stress. Expression of AtLPK1 was strongly induced by abscisic acid, methyl jasmonate, salicylic acid and stress treatments. Overexpression of AtLPK1 in Arabidopsis resulted in enhanced seed germination and cotyledon greening under high salinity condition, while antisense transgenic lines were more sensitive to salt stress. Activity of three abiotic stress responsive genes, RD29A, RD29B and COR15A, was elevated in AtLPK1-overexpressing plants than that in wild type (WT) plants with salt treatment, whereas the transcript level of these genes in antisense plants decreased compared with WT. Furthermore, AtLPK1-overexpressing plants displayed increased resistance to infection by Botrytis cinerea and exhibited stronger expression of a group of defense-related genes than did WT. The data implicates AtLPK1 plays essential roles at both abiotic and biotic stress response in Arabidopsis thaliana., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.) more...

Brassinosteroids (BRs) are steroid hormones that participate in multiple biological processes. In this paper, we characterized a classic rice mutant Fn189 (dwarf54, d54) showing semi-dwarf stature and erect leaves. The coleoptile elongation and root growth was less affected in Fn189 than wild-type plant by the exogenous application of eBL, the most active form of BRs. Lamina joint inclination assay and morphological analysis in darkness further showed that Fn189 mutant plant was insensitive to exogenous eBL. Through map-based cloning, Fn189 was found to be a novel allelic mutant of the DWARF 61 (D61) gene, which encodes the putative BRs receptor OsBRI1. A single base mutation caused the I834F substitution in the OsBRI1 kinase domain. Consequently, kinase activity of OsBRI1 was found to decrease dramatically. Taken together, the kinase activity of OsBRI1 is essential for brassinosteroids to regulate normal plant growth and development in rice., (Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.) more...

Phytochrome (phy) signalling in plants may be transduced through protein phosphorylation. Mitogen-activated protein kinase (MAP-kinase, MAPK) activity and the effect of R (red) and FR (far-red) light irradiation on MAPK activity were studied in etiolated Cucumis sativus L. cotyledons. By in vitro protein phosphorylation and in-gel assays with myelin basic protein (MBP), a protein band (between 48 and 45 kDa) with MAPK-like activity was detected. The addition to the phosphorylation buffer of specific protein phosphatase (PTP) inhibitors (Na(3)VO(4) and NaF) and genistein, apigenin or PD98059 as MAPK inhibitors allowed us to confirm the MAPK activity of the protein band. Irradiation of etiolated cotyledons with FR light for 5, 10 or 60 min rapidly and transiently stimulated the MAPK activity of the protein band. This suggests that there was a very low fluence response (VLFR) of phys. In addition, 15 min of R light irradiation or a sequential treatment of 15 min of R plus 5 min of FR also increased MAPK activity. The stimulatory effect of R light was also attributed to the same photoreceptor, which suggests that MAPKs are involved in phytochrome signal transduction. Protein immunoprecipitation and immunoblotting analysis with the polyclonal antibody anti-pERK1/2 (Tyr 204) and the monoclonal antibody anti-phosphotyrosine PY20 allowed us to recognize the above mentioned protein band as two proteins with molecular masses (M(r)) of approximately 47 and 45 kDa, and MAPK activity. The biochemical and immunological properties showed by the proteins detected indicated that they were members of the MAPK family phosphorylated in tyrosine residues., (Copyright © 2012 Elsevier Masson SAS. All rights reserved.) more...

Papain-like cysteine protease activity that shows a unique transient expression profile in cotyledons of daikon radish during germination was detected. The enzyme showed a distinct elution pattern on DEAE-cellulose compared with cathepsin B-like and Responsive to dessication-21 cysteine protease. Although this activity was not detected in seed prior to imbibition, the activity increased markedly and reached a maximum at 2 days after imbibition and then decreased rapidly and completely disappeared after 5 days. Using cystatin-Sepharose, the 26 kDa cysteine protease (DRCP26) was isolated from cotyledons at 2 days after imbibition. The deduced amino acid sequence from the cDNA nucleotide sequence indicated that DRCP26 is an orthologue of Arabidopsis unidentified protein, germination-specific cysteine protease-1, belonging to the C1 family of cysteine protease predicted from genetic information. In an effort to characterize the enzymatic properties of DRCP26, the enzyme was purified to homogeneity from cotyledons at 48 h after imbibition. The best synthetic substrate for the enzyme was carbobenzoxy-Phe-Arg-4-methylcoumaryl-7-amide. All model peptides were digested to small peptides by the enzyme, suggesting that DRCP26 possesses broad cleavage specificity. These results indicated that DRCP26 plays a role in the mobilization of storage proteins in the early phase of seed germination. more...

Cysteine peptidases are the best characterized peptidases among those involved with storage protein mobilization during seed germination. In the present work we show two major groups of cysteine peptidase activities, one of higher (55 to 97 kDa) and other with lower (15 to 20 kDa) molecular masses which are temporally activated after 24 and 48 HAI, respectively, in germinating cowpeas. The former group is found both in protein bodies and in cytoplasmic fraction, while the latter is mostly present outside protein bodies. A third cysteine peptidase activity of ~37 kDa was specifically active at quiescent cotyledons and at 12 and 60 hours after imbibition (HAI). Main peptidase activities of albumin fractions were synchronizedly detected with radicle emergence at 36 HAI. Major vicilin mobilization was more pronounced from 60 HAI onwards and steadily increased until 144 HAI, when low levels of the smallest vicilin subunit were present. Cysteine peptidases were susceptible to iodoacetamide, E-64, iodoacetic acid, pCMB and β-mercaptoethanol, except for the ~37 kDa peptidase, which was not affected by any of the inhibitors. By a two-dimensional native/SDS-PAGE combination it was observed an apparent linear arrangement of protein breakdown products as well as of peptidase activity spots. The finding may indicate a complex set of sequential proteolytic events where peptidases induce or activate new peptidases, which may act upon different aggregates or zymogens, and these hydrolysis products appear in a line of constant decreasing Rf x Mr ratio. more...

Comparative analysis of the transport activity of proton pumps (plasmalemma H+-ATPase, vacuolar H+-ATPase, and vacuolar H+-pyrophosphatase) in the membrane preparations obtained from coleoptile cells ofetiolated maize seedlings (Zea mays L.) was carried out. The highest level ofvacuolar pyrophosphatase activity was observed during the early development of coleoptile cells under growth intensification through the elongation. The role of ATPase pumps of tonoplast and plasmalemma in the transport of hydrogen ions increases during further development. The plasmalemma activity in this process is higher. When the growth stops, the activity of proton pumps becomes significantly lower. Nevertheless, their substrate specificity and sensitivity to proton pump inhibitors do not change, which can be an evidence of physiological significance of pumps in the maintenance of cell homeostasis. more...

Promoter regions of each of the six AtBGAL gene of the subfamily a1 of Arabidopsis thaliana were used to drive the expression of the β-glucuronidase gene. The pattern of promoters (pAtBGAL) activity was followed by histological staining during plant development. pAtBGAL1, pAtBGAL3 and pAtBGAL4 showed a similar activity pattern, being stronger in cells and organs in expansion, and the staining decreasing when cell expansion decreased with age. That indicates a consistent involvement of the encoded β-galactosidases in cells undergoing cell wall extension or remodelling in cotyledons, leaves and flower buds. These promoters were also active in the calyptra cells and in pollen grains. pAtBGAL2 activity showed a clear relationship with hypocotyl elongation in both light and dark conditions and, like pAtBGAL1, pAtBGAL3 and pAtBGAL4, it was detected during the expansion of cotyledons, rosette leaves and cauline leaves. Its activity was also intense in the early stages of flower and fruit development. pAtBGAL5 was the only one among those from the subfamily a1 that was active in the trichomes that appear throughout the plant, indicating a high specificity of the AtBGAL5 protein and its involvement in the cell wall changes that accompany the formation of the trichome. The activity of pAtBGAL5 was also high in radicles and roots, except in the meristematic area of these organs, and during seed formation. Finally, the activity of pAtBGAL12 was mainly detected in meristematic zones of the plant: the leaf primordium, emerging secondary roots and developing seeds, which indicates an involvement in the differentiation process., (Copyright © 2012 Elsevier Masson SAS. All rights reserved.) more...

MAPKs (mitogen-activated protein kinases) are signalling components highly conserved among eukaryotes. Their diverse biological functions include cellular differentiation and responses to different extracellular stress stimuli. Although some substrates of MAPKs have been identified in plants, no information is available about whether amino acids in the primary sequence other than proline-directed phosphorylation (pS-P) contribute to kinase specificity towards substrates. In the present study, we used a random positional peptide library to search for consensus phosphorylation sequences for Arabidopsis MAPKs MPK3 and MPK6. These experiments indicated a preference towards the sequence L/P-P/X-S-P-R/K for both kinases. After bioinformatic processing, a number of novel candidate MAPK substrates were predicted and subsequently confirmed by in vitro kinase assays using bacterially expressed native Arabidopsis proteins as substrates. MPK3 and MPK6 phosphorylated all proteins tested more efficiently than did another MAPK, MPK4. These results indicate that the amino acid residues in the primary sequence surrounding the phosphorylation site of Arabidopsis MAPK substrates can contribute to MAPK specificity. Further characterization of one of these new substrates confirmed that At1g80180.1 was phosphorylated in planta in a MAPK-dependent manner. Phenotypic analyses of Arabidopsis expressing phosphorylation site mutant forms of At1g80180.1 showed clustered stomata and higher stomatal index in cotyledons expressing the phosphomimetic form of At1g80180.1, providing a link between this new MAPK substrate and the defined role for MPK3 and MPK6 in stomatal patterning. more...

Position-dependent patterning of hair and non-hair cells in the Arabidopsis thaliana root epidermis is a powerful system to study the molecular basis of cell fate specification. Here, we report an epidermal patterning mutant affecting the ADENOSINE DIMETHYL TRANSFERASE 1A (DIM1A) rRNA dimethylase gene, predicted to participate in rRNA posttranscriptional processing and base modification. Consistent with a role in ribosome biogenesis, DIM1A is preferentially expressed in regions of rapid growth, and its product is nuclear localized with nucleolus enrichment. Furthermore, DIM1A preferentially accumulates in the developing hair cells, and the dim1A point mutant alters the cell-specific expression of the transcriptional regulators GLABRA2, CAPRICE, and WEREWOLF. Together, these findings suggest that establishment of cell-specific gene expression during root epidermis development is dependent upon proper ribosome biogenesis, possibly due to the sensitivity of the cell fate decision to relatively small differences in gene regulatory activities. Consistent with its effect on the predicted S-adenosyl-l-Met binding site, dim1A plants lack the two 18S rRNA base modifications but exhibit normal pre-rRNA processing. In addition to root epidermal defects, the dim1A mutant exhibits abnormal root meristem division, leaf development, and trichome branching. Together, these findings provide new insights into the importance of rRNA base modifications and translation regulation for plant growth and development. more...

The mitochondrial ATP synthase (F(1)F(o) complex) is an evolutionary conserved multimeric protein complex that synthesizes the main bulk of cytosolic ATP, but the regulatory mechanisms of the subunits are only poorly understood in plants. In yeast, the δ-subunit links the membrane-embedded F(o) part to the matrix-facing central stalk of F(1). We used genetic interference and an inhibitor to investigate the molecular function and physiological impact of the δ-subunit in Arabidopsis thaliana. Delta mutants displayed both male and female gametophyte defects. RNA interference of delta resulted in growth retardation, reduced ATP synthase amounts, and increased alternative oxidase capacity and led to specific long-term increases in Ala and Gly levels. By contrast, inhibition of the complex using oligomycin triggered broad metabolic changes, affecting glycolysis and the tricarboxylic acid cycle, and led to a successive induction of transcripts for alternative respiratory pathways and for redox and biotic stress-related transcription factors. We conclude that (1) the δ-subunit is essential for male gametophyte development in Arabidopsis, (2) a disturbance of the ATP synthase appears to lead to an early transition phase and a long-term metabolic steady state, and (3) the observed long-term adjustments in mitochondrial metabolism are linked to reduced growth and deficiencies in gametophyte development. more...

The tightly bound proteins (TBPs), a protein group that remains attached to DNA either covalently or noncovalently after deproteinization, have been found in numerous eukaryotic species. Some TBPs isolated from mammalian and yeast cells possess phosphatase or kinase activity. The aim of this study was to characterize further TBPs in barley (Hordeum vulgare) cells. The spectra of TBPs varied in different organs of barley shoots (first leaves, coleoptile, and roots) and at different developmental stages of the plant. Some barley TBPs manifested phosphatase, probably Ser/Thr or dual Ser/Thr/Tyr activity. MALDI-TOF mass spectrometry of barley TBPs identified several proteins involved in chromatin rearrangement and regulation processes, including transcription factors, serpins, protein phosphatases and protein kinases, RNA helicases, and DNA topoisomerase II. more...

We have observed a novel, lesion mimic phenotype (LMP) in the cotyledons of cotton seedlings expressing an endochitinase gene from Trichoderma virens. This phenotype, however, is conditional and is elicited only when the transgenic seedlings are germinating on a medium that is devoid of mineral nutrients. The LMP manifests itself around the 5th day in the form of scattered, dry necrotic lesions on the cotyledons. The severity of the LMP is correlated with the level of transgene activity. Production of reactive oxygen species and activities of certain defense related enzymes and genes were substantially higher in the cotyledons of seedlings that were growing under mineral nutrient stress. Molecular and biochemical analyses indicated significantly higher-level activities of certain defense-related genes/enzymes at the onset of the phenotype. Treatment with methyl jasmonate can induce LMP in the cotyledons of wild-type (WT) seedlings similar to that observed in the endochitinase-expressing seedlings grown on nutrient-free medium. On the other hand, salicylic acid (SA), its functional analog, benzo(1,2,3) thiadiazole-7-carbothioic acid (BTH), and ibuprofen can rescue the LMP induced by the seedling-growth on nutrient-deficient medium. Nutrient deficiency-induced activation of a defense response appears to be the contributing factor in the development of LMP in endochitinase-expressing cotton seedlings., (Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.) more...

We previously reported that native tropical zone plants showed high acetylcholinesterase (AChE) activity during heat stress, and that AChE activity in endodermal cells of maize seedlings was increased by heat treatment. However, the physiological role of AChE in heat stressed plants is still unclear. Here we report (1) tissue-specific expression and subcellular localization of maize AChE, (2) elevation of AChE activity and possible post-translational modifications of this enzyme under heat stress, and (3) involvement of AChE in plant heat stress tolerance. Maize AChE was mainly expressed in coleoptile nodes and seeds. Maize AChE fused with green fluorescent protein (GFP) was localized in extracellular spaces of transgenic rice plants. Therefore, in maize coleoptile nodes and seeds AChE mainly functions in the cell wall matrix. After heat treatment, enhanced maize AChE activity was observed by in vitro activity measurement and by in situ cytochemical staining; transcript and protein levels, however, were not changed. Protein gel blot analysis revealed two AChE isoforms (upper and lower); the upper-form gradually disappeared after heat treatment. Thus, maize AChE activity might be enhanced through a post-translational modification response to heat stress. Finally, we found that overexpression of maize AChE in transgenic tobacco plants enhanced heat tolerance relative to that of non-transgenic plants, suggesting AChE plays a positive role in maize heat tolerance., (Copyright © 2011 Elsevier GmbH. All rights reserved.) more...

Genome analysis has indicated that plants, like animals, possess a variety of protease genes. However, bulk of putative proteases has not been characterized at the enzyme level. In this article, a novel enzyme that hydrolyses phenylalanyl-4-methylcoumaryl 7-amide (phenylalanyl-MCA) was purified from cotyledons of daikon radish by ammonium sulphate fractionation and successive chromatography with DEAE-cellulose, phenyl-Sepharose, Sephacryl S-200 and Mini-Q. The molecular mass of the enzyme was estimated to be 78 kDa by SDS-PAGE under reducing conditions and 74 kDa by gel filtration, indicating that the enzyme is a monomer. The deduced amino acid sequence from the cDNA nucleotide sequence indicated that the enzyme is an orthologue of Arabidopsis unidentified protein, acylpeptide hydrolase-like protein (AHLP; UniProt ID: Q9FG66) belonging to the prolyl oligopeptidase (POP) family of a serine-type peptidase predicted from genetic information. Good substrates identified for the enzyme include phenylalanyl-MCA, tyrosyl-MCA and enkephalin. Neither acylamino acid-releasing activity nor endopeptidase activity was detected. The enzyme cleaved enkephalin (YGGFM, YGGFL), whereas, BAM-12 P (YGGFMRRVGRPE) and dynorphin A (YGGFLRRIRPKLK) were not digested. These results suggested that the enzyme possesses strict size selectivity of substrate. We propose the name 'tyrosyl aminopeptidase' for the uncharacterized protein AHLP. more...