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Abstract Background Organ shape and size covariation (allometry) factors are essential concepts for the study of evolution and development. Although ample research has been conducted on organ shape and size, little research has considered the correlated variation of these two traits and quantitatively measured the variation in a common framework. The genetic basis of allometry variation in a single organ or among different organs is also relatively unknown. Results A principal component analysis (PCA) of organ landmarks and outlines was conducted and used to quantitatively capture shape and size variation in leaves and petals of multiparent advanced generation intercross (MAGIC) populations of Arabidopsis thaliana. The PCA indicated that size variation was a major component of allometry variation and revealed negatively correlated changes in leaf and petal size. After quantitative trait loci (QTL) mapping, five QTLs for the fourth leaf, 11 QTLs for the seventh leaf, and 12 QTLs for petal size and shape were identified. These QTLs were not identical to those previously identified, with the exception of the ER locus. The allometry model was also used to measure the leaf and petal allometry covariation to investigate the evolution and genetic coordination between homologous organs. In total, 12 QTLs were identified in association with the fourth leaf and petal allometry covariation, and eight QTLs were identified to be associated with the seventh leaf and petal allometry covariation. In these QTL confidence regions, there were important genes associated with cell proliferation and expansion with alleles unique to the maximal effects accession. In addition, the QTLs associated with life-history traits, such as days to bolting, stem length, and rosette leaf number, which were highly coordinated with climate change and local adaption, were QTL mapped and showed an overlap with leaf and petal allometry, which explained the genetic basis for their correlation. Conclusions This study explored the genetic basis for leaf and petal allometry and their interaction, which may provide important information for investigating the correlated variation and evolution of organ shape and size in Arabidopsis.

The unfolded protein response (UPR) is activated to sustain cell survival by reducing misfolded protein accumulation in the endoplasmic reticulum (ER). The UPR also promotes cell death when the ER stress is severe. However, the underlying molecular mechanisms of UPR activity regulation and cell death transition are less understood in plants. Arabidopsis GAAP1 and GAAP3 are involved in the regulation of UPR and cell death. Five GAAP gene members are found in Arabidopsis. Here, we analyzed the function of GAAP2 in addition to GAAP1 and GAAP3 in ER stress response using single, double, and triple mutants. Results showed that single or double or triple mutants reduced plant survival and enhanced cell death under ER stress. And the sensitivity increased with the number of mutation genes increase. Quantitative real-time polymerase chain reaction analysis showed that mutation in triple genes promoted UPR signaling when confronted with mild ER stress, advanced SA target genes upregulation when confronted with severe stress. Moreover, Quantitative detection by UPLC-ESI-MS/MS showed that ER stress upregulated salicylic acid (SA) content in plants. These data suggest that GAAP1 to GAAP3 played redundant roles in cell death resistance and fine tuning UPR activation. And the anti-cell death function of GAAPs might be achieved by impairing the up-regulation of the SA pathway under ER stress.

Heavy-ion beam irradiation is one of the principal methods used to create mutants in plants. Research on mutagenic effects and molecular mechanisms of radiation is an important subject that is multi-disciplinary. Here, we re-sequenced 11 mutagenesis progeny (M3) Arabidopsis thaliana lines derived from carbon-ion beam (CIB) irradiation, and subsequently focused on substitutions and small insertion-deletion (INDELs). We found that CIB induced more substitutions (320) than INDELs (124). Meanwhile, the single base INDELs were more prevalent than those in large size (≥2 bp). In details, the detected substitutions showed an obvious bias of C > T transitions, by activating the formation of covalent linkages between neighboring pyrimidine residues in the DNA sequence. An A and T bias was observed among the single base INDELs, in which most of these were induced by replication slippage at either the homopolymer or polynucleotide repeat regions. The mutation rate of 200-Gy CIB irradiation was estimated as 3.37 × 10−7 per site. Different from previous researches which mainly focused on the phenotype, chromosome aberration, genetic polymorphism, or sequencing analysis of specific genes only, our study revealed genome-wide molecular profile and rate of mutations induced by CIB irradiation. We hope our data could provide valuable clues for explaining the potential mechanism of plant mutation breeding by CIB irradiation.

Soil salinization, which is the accumulation of salt in soil, can have a negative impact on crop growth and development by creating an osmotic stress that can reduce water uptake and cause ion toxicity. The NHX gene family plays an important role in plant response to salt stress by encoding for Na+/H+ antiporters that help regulate the transport of sodium ions across cellular membranes. In this study, we identified 26 NHX genes in three cultivars of Cucurbita L., including 9 Cucurbita moschata NHXs (CmoNHX1-CmoNHX9), 9 Cucurbita maxima NHXs (CmaNHX1-CmaNHX9) and 8 Cucurbita pepo NHXs (CpNHX1-CpNHX8). The evolutionary tree splits the 21 NHX genes into three subfamilies: the endosome (Endo) subfamily, the plasma membrane (PM) subfamily, and the vacuole (Vac) subfamily. All the NHX genes were irregularly distributed throughout the 21 chromosomes. 26 NHXs were examined for conserved motifs and intron-exon organization. These findings suggested that the genes in the same subfamily may have similar functions while genes in other subfamilies may have functional diversity. The circular phylogenetic tree and collinearity analysis of multi-species revealed that Cucurbita L. had a substantially greater homology relationship than Populus trichocarpa and Arabidopsis thaliana in terms of NHX gene homology. We initially examined the cis-acting elements of the 26 NHXs in order to investigate how they responded to salt stress. We discovered that the CmoNHX1, CmaNHX1, CpNHX1, CmoNHX5, CmaNHX5, and CpNHX5 all had numerous ABRE and G-box cis-acting elements that were important to salt stress. Previous transcriptome data showed that in the mesophyll and veins of leaves, many CmoNHXs and CmaNHXs, such as CmoNHX1, responded significantly to salt stress. In addition, we heterologously expressed in A. thaliana plants in order to further confirm the response of CmoNHX1 to salt stress. The findings demonstrated that during salt stress, A. thaliana that had CmoNHX1 heterologously expression was found to have decreased salt tolerance. This study offers important details that will aid in further elucidating the molecular mechanism of NHX under salt stress. [ABSTRACT FROM AUTHOR]

NAC (NAM, ATAF, CUC) is a class of transcription factors involved in plant growth regulation, abiotic stress responses, morphogenesis and metabolism. Salvia miltiorrhiza is an important Chinese medicinal herb, but the characterization of NAC genes in this species is limited. In this study, based on the Salvia miltiorrhiza genomic databases, 82 NAC transcription factors were identified, which were divided into 14 groups. Meanwhile, phylogenetic analysis, gene structure, chromosomal localization and potential role of SmNACs in abiotic stress conditions were also studied. The results revealed that some SmNACs had different structures than others, which advised that these genes may have multiple/distinct functions. Real-time quantitative polymerase chain reaction (RT-qPCR) analysis showed that SmNACs exhibited differential expression patterns under salt and drought stress. The NaCl induced salinity treatments modulated the expression of several SmNAC genes more in roots compared with leaves. Conversely, under drought stress conditions, more genes were upregulated in leaves compared with roots. These results will be useful for the further study involved in the functional characteristics of SmNAC genes, especially in response to salt and drought stresses, thereby may facilitate genetic breeding in Salvia miltiorrhiza. [ABSTRACT FROM AUTHOR]

Protoplast transient expression is a powerful strategy for gene functional characterization, especially in biochemical mechanism studies. We herein developed a highly efficient transient expression system for apple protoplasts. The abilities of the Arabidopsis thaliana and Malus domestica ubiquitin-10 (AtUBQ10 and MdUBQ10) promoters to drive the expression of multiple genes were compared with that of the CaMV 35S promoter, and the results revealed that the AtUBQ10 and MdUBQ10 promoters were more efficient in apple protoplasts. With this system, we demonstrated that active AtMKK7ac could activate MAPK6/3/4 signaling cascades, which further regulated MdWRKY33 phosphorylation and stability in apple. Furthermore, the ligand-induced interaction between the immune receptor AtFLS2 and the coreceptor AtBAK1 was reconstituted in apple protoplasts. We also found that the stability of the bacterial effector AvrRpt2 was regulated by feedback involving auxin and the immune regulator RIN4. The system established herein will serve as a useful tool for the molecular and biochemical analyses of apple genes. [ABSTRACT FROM AUTHOR]

Heat stress is an environmental challenge that reduces plant productivity and growth. Plants have developed corresponding mechanisms to survive this adverse environmental stress. To demonstrate the mechanisms of how plants adapt to the environmental challenge, the heat response experiments involving Arabidopsis thaliana were retrieved from the GEO database. After quantile normalization of the GEO raw data, the differentially expressed genes (DEGs) in response to heat stress were identified by robust rank aggregation (RRA) algorithm, including 384 up-regulated and 302 down-regulated genes. Then, systematic bioinformatics analyses disclosed that the up-regulated DEGs were mainly related to protein refolding, abscisic acid catabolic process, potassium ion import, response to hydrogen peroxide, cytochrome complex assembly, and apoptotic process, and the down-regulated DEGs were involved in microsporocyte differentiation, syncytium formation, adventitious development, glutathione metabolism, and glycine metabolic process. The up-regulated DEGs also had more complicated PPI interactions than the down-regulated DEGs, and potential core genes of heat stress tolerance were provided. Furthermore, the mRNA expression of core genes Hsp70-2 (At5g02490), Hsp70-3 (At3g09440), and Hsp70-4 (At3g12580) has been measured to validate the outcome of integrated bioinformatics analysis. Our work will extend our understanding of heat-responsive mechanisms and these DEGs might be potential markers for plant heat stress-resistance studies.

Cold stress is a major environmental factor that limits plant growth and productivity. Plants have evolved various strategies to adapt to these environmental conditions. To better explain the mechanisms used to survive environmental challenges, we retrieved the cold-responsive genes of Arabidopsis thaliana from the Gene Expression Omnibus (GEO) database. The GEO raw data were normalized by the quantile method, and then the differentially expressed genes (DEGs) under cold stress were screened using the robust rank aggregation (RRA) algorithm, including 261 upregulated and 177 downregulated genes out of more than 20,000 genes. Further, the integrated bioinformatics analyses of PUBMED, PANTHER, DAVID, and STRING indicated that the upregulated DEGs were involved in cellular response to red light, negative regulation of circadian rhythm, photoprotection, monosaccharide transport, cold acclimation, and phosphate ion homeostasis, while the downregulated DEGs were associated with the indole glucosinolate biosynthetic process, regulation of RNA splicing, water transport, cell wall modification, cell wall loosening, cellular water homeostasis, and cell wall homeostasis. Furthermore, the up-regulated DEGs had about four times protein-protein-interactions (PPIs) than the down-regulated DEGs, and the cold-responsive genes were identified using Cytoscape software. Furthermore, qRT-PCR of low-temperature-responsive protein 78 (LTI78), transducin family protein (SWA1), and arginine methyltransferase 11 (PRMT11) were performed to validate the outcome of integrated bioinformatics analysis. Our work will improve our knowledge of cold-responsive mechanisms and these DEGs might be targets for plant cold stress-resistance research.

AtDjB1 is a mitochondria-located J-protein in Arabidopsis thaliana. It is involved in the regulation of plant growth and development; however, the exact mechanisms remain to be determined. We performed comparison analyses of phenotypes, auxin signalling, redox status, mitochondrial structure and function using wild-type plants, AtDjB1 mutants, rescued AtDjB1 mutants by AtDjB1 or YUCCA2 (an auxin synthesis gene), and AtDjB1 overexpression plants. AtDjB1 mutants (atj1-1 or atj1-4) exhibited inhibition of growth and development and reductions in the level of IAA and the expression of YUCCA genes compared to wild-type plants. The introduction of AtDjB1 or YUCCA2 into atj1-1 largely rescued phenotypic defects and the IAA level, indicating that AtDjB1 probably regulates growth and development via auxin. Furthermore, atj1-1 plants displayed a significant reduction in amount/activity of mitochondrial complex I compared to wild-type plants; this resulted in the accumulation of reactive oxygen species (ROS). Moreover, exogenous H2O2 markedly inhibited the expression of YUCCA genes in wild-type plants. In contrast, the reducing agent ascorbate increased the expression of YUCCA genes and IAA level in atj1-1 plants, indicating that the low auxin level observed in atj1-1 was probably due to the high oxidation status. Overall, the data presented here suggest that AtDjB1 is required for mitochondrial complex I activity and regulates growth and development through ROS-mediated auxin signalling in Arabidopsis. [ABSTRACT FROM AUTHOR]

Salt stress negatively affects plant growth and crop productivity. As an ideal model pathway of salt tolerance in glycophyte. To better understand the molecular mechanisms of salt-response in glycophyte, 466 of 15,768 Arabidopsis thaliana proteins with the GO term of biological with known genetic background, Arabidopsis thaliana has been widely applied to disclose the process ‘response to salt stress’ were retrieved from UniPort and analyzed by bioinformatics tools of PANTHER, DAVID, KEGG, Cytoscape and STRING. Our results not only indicated the involvement of salt-responsive proteins in various pathways and interaction networks, but also demonstrated the more complicated cross-tolerances to both abiotic stresses (osmosis, water deprivation, abscisic acid, cold, heat, light and wounding) and biotic stresses (bacterium and fungus) and multiple subcellular locations of these salt-responsive proteins. Furthermore, protein activities of superoxide dismutase (SOD) and peroxidase (POD) in Arabidopsis thaliana were determined under salt, cold and osmotic stresses, which validated the hypothesis of cross-tolerance to multiple stresses. Our work will greatly improve the current knowledge of salt tolerance mechanism in glycophytes and provide potential salt-responsive candidates for promoting plant growth and increasing crop output.

A balanced supply of essential nutrients is an important factor influencing root architecture in many plants, yet data related to the interactive effects of two nutrients on root growth are limited. Here, we investigated the interactive effect between phosphorus (P) and magnesium (Mg) on root growth of Arabidopsis grown in pH-buffered agar medium at different P and Mg levels. The results showed that elongation and deviation of primary roots were directly correlated with the amount of P added to the medium but could be modified by the Mg level, which was related to the root meristem activity and stem-cell division. High P enhanced while low P decreased the tip-focused fluorescence signal of auxin biosynthesis, transport, and redistribution during elongation of primary roots; these effects were greater under low Mg than under high Mg. The altered root growth in response to P and Mg supply was correlated with AUX1, PIN2, and PIN3 mRNA abundance and expression and the accumulation of the protein. Application of either auxin influx inhibitor or efflux inhibitor inhibited the elongation and increased the deviation angle of primary roots, and decreased auxin level in root tips. Furthermore, the auxin-transport mutants aux1-22 and eir1-1 displayed reduced root growth and increased the deviation angle. Our data suggest a profound effect of the combined supply of P and Mg on the development of root morphology in Arabidopsis through auxin signals that modulate the elongation and directional growth of primary root and the expression of root differentiation and development genes. [ABSTRACT FROM AUTHOR]

Previously, we reported that although the Arabidopsis (Arabidopsis thaliana) Xyloglucan Endotransglucosylase-Hydrolase31 (XTH31) has predominately xyloglucan endohydrolase activity in vitro, loss of XTH31 results in remarkably reduced in vivo xyloglucan endotransglucosylase (XET) action and enhanced A1 resistance. Here, we report that XTH17, predicted to have XET activity, binds XTH31 in yeast (Saccharomyces cerevisiae) two-hybrid and coimmunoprecipitations assays and that this interaction may be required for XTH17 XET activity in planta. XTH17 and XTH31 may be colocalized in plant cells because tagged XTH17 fusion proteins, like XTH31 fusion proteins, appear to target to the plasma membrane. XTH17 expression, like that of XTH3I, was substantially reduced in the presence of aluminum (A1), even at concentrations as low as 10 µM for 24 h or 25 µM for just 30 min. Agrobacterium tumefaciens-mediated transfer DNA insertion mutant of XTH17, xth17, showed low XET action and had moderately shorter roots than the wild type but was more A1 resistant than the wild type. Similar to xth31, xthl7 had low hemicellulose content and retained less A1 in the cell wall. These data suggest a model whereby XTH17 and XTH31 may exist as a dimer at the plasma membrane to confer in vivo XET action, which modulates cell wall Al-binding capacity and thereby affects A1 sensitivity in Arabidopsis. [ABSTRACT FROM AUTHOR]

In fungi and metazoans, extracellular signals are often perceived by G-protein-coupled receptors (GPCRs) and transduced through heterotrimeric G-protein complexes to downstream targets. Plant heterotrimeric G proteins are also involved in diverse biological processes, but little is known about their upstream receptors. Moreover, the presence of bona fide GPCRs in plants is yet to be established. In Arabidopsis (Arabidopsis thaliana), heterotrimeric G protein consists of one Gα subunit (G PROTEIN α-SUBUNIT1), one Gβ subunit (ARABIDOPSIS G PROTEIN β-SUBUNIT1 [AGB1]), and three Gγs subunits (ARABIDOPSIS G PROTEIN γ-SUBUNIT1 [AGG1], AGG2, and AGG3). We identified AGB1 from a suppressor screen of BAK1-interacting receptor-like kinasel-1 (bit1-1), a mutant that activates cell death and defense responses mediated by the receptor-like kinase (RLK) SUPPRESSOR OF BIRI-1. Mutations in AGB1 suppress the cell death and defense responses in bir1-1 and transgenic plants overexpressing SUPPRESSOR OF BIRI-1. In addition, agb1 mutant plants were severely compromised in immunity mediated by three other RLKs, FLAGELLIN-SENSITIVE2 (FLS2), Elongation Factor-TU RECEPTOR (EFR), and CHITIN ELICITOR RECEPTOR KINASE1 (CERK1), respectively. By contrast, G PROTEIN α-SUBUNIT1 is not required for either cell death in bir1-1 or pathogen-associated molecular pattern-triggered immunity mediated by FLS2, EFR, and CERK1. Further analysis of agg1 and agg2 mutant plants indicates that AGG1 and AGG2 are also required for pathogen-associated molecular pattern-triggered immune responses mediated by FLS2, EFR, and CERK1, as well as cell death and defense responses in birl-1. We hypothesize that the Arabidopsis heterotrimeric G proteins function as a converging point of plant defense signaling by mediating responses initiated by multiple RLKs, which may fulfill equivalent roles to GPCRs in fungi and animals. [ABSTRACT FROM AUTHOR]

The function of PsBRC1, the pea (Pisum sativum) homolog of the maize (Zea mays) TEOSINTE BRANCHED1 a Arabidopsis (Arabidopsis thaliana) BRANCHED1 (AtBRC1) genes, was investigated. The pea Psbrcl mutant displays an increased shoot-branching phenotype, is able to synthesize strigolactone (SL), and does not respond to SL application. The level of pleiotropy of the SL-deficient ramosusl (rms1) mutant is higher than in the Psbrc1 mutant, rmsl exhibiting a relatively dwarf phenotype and more extensive branching at upper nodes. The PsBRC1 gene is mostly expressed in the axillary bud and is transcriptionally up-regulated by direct application of the synthetic SL GR24 and down-regulated by the cytokinin (CK) 6-benzylaminopurine. The results suggest that PsBRC1 may have a role in integrating SL and CK signals and that SLs act directly within the bud to regulate its outgrowth. However, the Psbrc1 mutant responds to 6-benzylaminopurine application and decapitation by increasing axillary bud length, implicating a PsBRC1-independent component of the CK response in sustained bud growth. In contrast to other SL-related mutants, the Psbrc1 mutation does not cause a decrease in the CK zeatin riboside in the xylem sap or a strong increase in RMS1 transcript levels, suggesting that the RMS2-dependent feedback is not activated in this mutant. Surprisingly, the double rmsl Psbrc1 mutant displays a strong increase in numbers of branches at cotyledonary nodes, whereas branching at upper nodes is not significantly higher than the branching in rms1. This phenotype indicates a localized regulation of branching at these nodes specific to pea. [ABSTRACT FROM AUTHOR]

The cell wall (CW) has been recognized as the major target of aluminum (Al) toxicity. However, the components responsible for Al accumulation and the mechanisms of Al-induced CW function disruption are still elusive. The contribution of different CW components (pectin, hemicellulose 1 [HC1], and HC2) to adsorb AI and the effect of A1 on xyloglucan endotransglucosylase/ hydrolyase activity were investigated in Arabidopsis (Arabidopsis thaliana) in this study. A fractionation procedure was optimized to effectively extract different CW components, especially to prevent the HC fraction from pectin contamination. When CW materials extracted from Al-treated roots (50 µM Al for 24 h) were fractionated, about 75% of CW Al accumulated in the HCl fraction. A time-dependent kinetic study showed that only when the HCl fraction was removed was the amount of Al adsorbed decreased sharply. In vivo localization of xyloglucan endotransglucosylase (XET) activity showed that AI greatly inhibited this enzyme activity within 30 min of exposure, which was concomitant with Al-induced callose deposition in roots. Results from real-time reverse transcription-polymerase chain reaction indicated that three genes may constitute the major contributors to XET activity and that the inhibition of XET activity by Al is caused by transcriptional regulation. These results, to our knowledge for the first time, demonstrate that HC is the major pool for Al accumulation. Furthermore, Al-induced reduction in XET activity could play an important role in Al-induced root growth inhibition. [ABSTRACT FROM AUTHOR]

Arabidopsis (Arabidopsis thaliana) suppressor of npr1-1, constitutive1 (snc1) contains a gain-of-function mutation in a Toll/interleukin receptor-nucleotide binding site-leucine-rich repeat Resistance (R) protein and it has been a useful tool for dissecting R-protein-mediated immunity. Here we report the identification and characterization of snc4-1D, a semidominant mutant with snc1-like phenotypes, snc4-1D constitutively expresses defense marker genes PR1, PR2, and PDF1.2, and displays enhanced pathogen resistance. Map-based cloning of SNC4 revealed that it encodes an atypical receptor-like kinase with two predicted extracellular glycerophosphoryl diester phosphodiesterase domains. The snc4-1D mutation changes an alanine to threonine in the predicted cytoplasmic kinase domain. Wild-type plants transformed with the mutant snc4-1D gene displayed similar phenotypes as snc4-1D, suggesting that the mutation is a gain-of-function mutation. Epistasis analysis showed that NON-RACE-SPECIFIC DISEASE RESISTANCE1 is required for the snc4-1D mutant phenotypes. In addition, the snc4-1D mutant phenotypes are partially suppressed by knocking out MAP KINASE SUBSTRATE1, a positive defense regulator associated with MAP KINASE4. Furthermore, both the morphology and constitutive pathogen resistance of snc4-1D are partially suppressed by blocking jasmonic acid synthesis, suggesting that jasmonic acid plays an important role in snc4-1D-mediated resistance. Identification of snc4-1D provides us a unique genetic system for analyzing the signal transduction pathways downstream of receptor-like kinases. [ABSTRACT FROM AUTHOR]

Plant Resistance (R) genes encode immune receptors that recognize pathogens and activate defense responses. Because of fitness costs associated with maintaining R protein-mediated resistance, expression levels of R genes have to be tightly regulated. However, mechanisms on how R-gene expression is regulated are poorly understood. Here we show that MODIFIER OF snc1, 1 (MOS1) regulates the expression of SUPPRESSOR OF npr1-1, CONSTITUTIVE1 (SNC1), which encodes a Toll/interleukin receptor-nucleotide binding site-leucine-rich repeat type of R protein in Arabidopsis (Arabidopsis thaliana). In the mos1 loss-of-function mutant plants, snc1 expression is repressed and constitutive resistance responses mediated by snc1 are lost. The repression of snc1 expression in mos1 is released by knocking out DECREASE IN DNA METHYLATION1. In mos1 mutants, DNA methylation in a region upstream of SNCI is altered. Furthermore, expression of snc1 transgenes using the native promoter does not require MOS1, indicating that regulation of SNC1 expression by MOS1 is at the chromatin level. Map-based cloning of MOS1 revealed that it encodes a novel protein with a HLA-B ASSOCIATED TRANSCRIPT2 (BAT2) domain that is conserved in plants and animals. Our study on MOS1 suggests that BAT2 domain-containing proteins may function in regulation of gene expression at chromatin level. [ABSTRACT FROM AUTHOR]

Systemic acquired resistance (SAR) is a plant immune response induced by local necrotizing pathogen infections. Expression of SAR in Arabidopsis (Arabidopsis thaliana) plants correlates with accumulation of salicylic acid (SA) and up-regulation of Pathogenesis-Related (PR) genes. SA is an essential and sufficient signal for SAR. In a genetic screen to search for negative regulators of PR gene expression and SAR, we found a new mutant that is hypersensitive to SA and exhibits enhanced induction of PR genes and resistance against the virulent oomycete Hyaloperonospora arabidopsidis Noco2. The enhanced pathogen resistance in the mutant is Nonexpressor of PR genesi independent. The mutant gene was identified by map-based cloning, and it encodes a protein with high homology to Replication Factor C Subunit3 (RFC3) of yeast and other eukaryotes; thus, the mutant was named rfc3-1. rfc3-1. mutant plants are smaller than wild-type plants and have narrower leaves and petals. On the epidermis of true leaves, there are fewer cells in rfc3-TI compared with the wild type. Cell production rate is reduced in rfc3-TI mutant roots, indicating that the mutated RFC3 slows down cell proliferation. As Replication Factor C is involved in replication-coupled chromatin assembly, our data suggest that chromatin assembly and remodeling may play important roles in the negative control of PR gene expression and SAR. [ABSTRACT FROM AUTHOR]

Pathogen/microbe-associated molecular patterns (PAMPs/MAMPs) trigger plant immunity that forms the first line inducible defenses in plants. The regulatory mechanism of MAMP-triggered immunity, however, is poorly understood. Here, we show that Arabidopsis thaliana transcription factors ETHYLENE INSENSITIVE3 (EIN3) and ETHYLENE INSENSITIVE3-LIKE1 (EL previously known to mediate ethylene signaling, also negatively regulate PAMP-triggered immunity. Plants lacking EIN3 an EIL1 display enhanced PAMP defenses and heightened resistance to Pseudomonas syringae bacteria. Conversely, plants overaccumulating EIN3 are compromised in PAMP defenses and exhibit enhanced disease susceptibility to Pseudomonas syringae. Microarray analysis revealed that EIN3 and EIL1 negatively control PAMP response genes. Further analyses indicated that SALICYLIC ACID INDUCTION DEFICIENT2 (SID2), which encodes isochorismate synthase required for pathogen-induced biosynthesis of salicylic acid (SA), is a key target of EIN3 and EIL1. Consistent with this, the ein3-1 eil1- double mutant constitutively accumulates SA in the absence of pathogen attack, and a mutation in SID2 restores normal susceptibility in the ein3 eil1 double mutant. EIN3 can specifically bind SID2 promoter sequence in vitro and in vivo. Taken together, our data provide evidence that EIN3/EIL1 directly target SID2 to downregulate PAMP defenses. [ABSTRACT FROM AUTHOR]

Plant immune responses depend on dynamic signaling events across the nuclear envelope through nuclear pores. Nuclear accumulation of certain resistance (R) proteins and downstream signal transducers are critical for their functions, but it is not understood how these processes are controlled. Here, we report the identification, cloning, and analysis of Arabidopsis thaliana modifier of snc1, 7 (mos7-1), a partial loss-of-function mutation that suppresses immune responses conditioned by the autoactivated R protein sncl (for suppressor of npr1-1, constitutive 1). mos7-1 single mutant plants exhibit defects in basal and R protein-mediated immunity and in systemic acquired resistance but do not display obvious pleiotropic defects in development, salt tolerance, or plant hormone responses. MOST is homologous to human and Drosophila melanogaster nucleoporin Nup88 and resides at the nuclear envelope. In animals, Nup88 attenuates nuclear export of activated NF-κB transcription factors, resulting in nuclear accumulation of NF-κB. Our analysis shows that nuclear accumulation of sncl and the defense signaling components Enhanced Disease Susceptibility 1 and Nonexpresser of PR genes 1 is significantly reduced in mos7-1 plants, while nuclear retention of other tested proteins is unaffected. The data suggest that specifically modulating the nuclear concentrations of certain defense proteins regulates defense outputs. [ABSTRACT FROM AUTHOR]

The Arabidopsis thaliana suppressor of npr1-1, constitutive 1 (snc1) mutant contains a gain-of-function mutation in a Toll Interleukin1 receptor-nucleotide binding-Leu-rich repeat-type resistance gene (R-gene), which leads to constitutive activation of disease resistance response against pathogens. In a screen for suppressors of snc1, a recessive mutation, designated mos3 (for modifier of snc1,3), was found to suppress the constitutive pathogenesis-related gene expression and resistance to virulent Pseudomonas syringae maculicola ES4326 and Peronospora parasitica Noco2 in snc1. In addition, mos3 is also compromised in resistance mediated by Resistance to Peronospora parasitica 4 (RPP4), Resistance to Pseudomonas syringae pv maculicola (RPM1), and Resistance to Pseudomonas syringae 4 (RPS4). Single mutant mos3 plants exhibited enhanced disease susceptibility to P. s. pv maculicola ES4326, suggesting that MOS3 is required for basal resistance to pathogens as well. mos3-1 was identified by map-based cloning, and it encodes a protein with high sequence similarity to human nucleoporin 96. Localization of the MOS3-green fluorescent protein fusion to the nuclear envelope further indicates that MOS3 may encode a nucleoporin, suggesting that nuclear and cytoplasmic trafficking plays an important role in both R-gene-mediated and basal disease resistance. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (H2O2) is an important signaling molecule in ethylene-induced stomatal closure in Arabidopsis thaliana. Early studies on the sources of H2O2 mainly focused on NADPH oxidases and cell-wall peroxidases. Here, we report the involvement of polyamine oxidases (PAOs) in ethylene-induced H2O2 production in guard cells. In Arabidopsis epidermal peels, application of PAO inhibitors caused the failure of ethylene to induce H2O2 production and stomatal closure. Results of quantitative RT-PCR analysis and pharmacological experiments showed that AtPAO2 and AtPAO4 transcripts and activities of PAOs were both induced by ethylene. In transgenic Arabidopsis plants over-expressing AtPAO2 and AtPAO4, stomatal movement was more sensitive to ethylene treatment and H2O2 production was also significantly induced. The increased H2O2 production in the transgenic lines compared to the wild-type plants suggests that AtPAO2 and AtPAO4 probably are involved in ethylene-induced H2O2 production. Several factors which induce stomatal closure such as dehydration and high salinity all enhanced the expression of AtPAO2 and AtPAO4 to different degrees. Moreover, GFP-AtPAOs fusion protein localized in the nucleus, cytoplasm, and cell wall of the guard cells. Therefore, our results strongly indicated that PAO is a source of H2O2 generation in Arabidopsis guard cells and plays crucial roles in stomatal movement.

Lysophospholipids (LPLs) are important lipid-signaling molecules in plants, of which lysophosphatidylcholine (lysoPC) is one of the most well-characterized LPLs, having important roles in plant stress responses. It is broken down by lysophospholipases, but the molecular mechanism involved in lysoPC degradation is unclear. Recombinant Arabidopsis thaliana ACYL-CoA-BINDING PROTEIN2 (AtACBP2) has been reported to bind lysoPC via its acyl-CoA-binding domain and also LYSOPHOSPHOLIPASE 2 (AtLYSOPL2) via its ankyrin repeats in vitro. To investigate the interactions of AtACBP2 with AtLYSOPL2 and lysoPC in more detail, we conducted isothermal titration calorimetry with AtACBP270-354, an AtACBP2 derivative consisting of amino acids 70-354, containing both the acyl-CoA-binding domain and ankyrin repeats. We observed that the interactions of AtACBP270-354 with AtLYSOPL2 and lysoPC were both endothermic, favored by solvation entropy and opposed by enthalpy, with dissociation constants in the micromolar range. Of note, three AtLYSOPL2 catalytic triad mutant proteins (S147A, D268A, and H298A) bound lysoPC only weakly, with an exothermic burst and dissociation constants in the millimolar range. Furthermore, the binding affinity of lysoPC-premixed AtACBP270-354 to AtLYSOPL2 was 10-fold higher than that of AtACBP270-354 alone to AtLYSOPL2. We conclude that AtACBP2 may play a role in facilitating a direct interaction between AtLYSOPL2 and lysoPC. Our results suggest that AtACBP270-354 probably binds to lysoPC through a hydrophobic interface that enhances a hydrotropic interaction of AtACBP270-354 with AtLYSOPL2 and thereby facilitates AtLYSOPL2's lysophospholipase function. [ABSTRACT FROM AUTHOR]

The function of PsBRC1, the pea (Pisum sativum) homolog of the maize (Zea mays) TEOSINTE BRANCHED1 a Arabidopsis (Arabidopsis thaliana) BRANCHED1 (AtBRC1) genes, was investigated. The pea Psbrcl mutant displays an increased shoot-branching phenotype, is able to synthesize strigolactone (SL), and does not respond to SL application. The level of pleiotropy of the SL-deficient ramosusl (rms1) mutant is higher than in the Psbrc1 mutant, rmsl exhibiting a relatively dwarf phenotype and more extensive branching at upper nodes. The PsBRC1 gene is mostly expressed in the axillary bud and is transcriptionally up-regulated by direct application of the synthetic SL GR24 and down-regulated by the cytokinin (CK) 6-benzylaminopurine. The results suggest that PsBRC1 may have a role in integrating SL and CK signals and that SLs act directly within the bud to regulate its outgrowth. However, the Psbrc1 mutant responds to 6-benzylaminopurine application and decapitation by increasing axillary bud length, implicating a PsBRC1-independent component of the CK response in sustained bud growth. In contrast to other SL-related mutants, the Psbrc1 mutation does not cause a decrease in the CK zeatin riboside in the xylem sap or a strong increase in RMS1 transcript levels, suggesting that the RMS2-dependent feedback is not activated in this mutant. Surprisingly, the double rmsl Psbrc1 mutant displays a strong increase in numbers of branches at cotyledonary nodes, whereas branching at upper nodes is not significantly higher than the branching in rms1. This phenotype indicates a localized regulation of branching at these nodes specific to pea. [ABSTRACT FROM AUTHOR]