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Background and aims: As the immobility of inorganic phosphorus (P) in soil, the acquisition of P by sessile plants is limited. γ-Aminobutyric acid (GABA) as a signal molecule and a metabolite can regulate plants to cope with various stresses. However, whether GABA could contribute to the adaption to low P stress in apple plants remains unclear. Methods: This study combined different methods to detect the induction of auxin (IAA) synthesis by GABA to improve the tolerance of apple seedlings to low P stress (including growth and development analysis, reactive oxygen species (ROS) clearance effect, root structure analysis, multiple factorial analysis (MFA), gene expression analysis). Results: Exogenous GABA improved the growth of apple seedlings under low P conditions, reduced the ROS accumulation, and promoted the photosynthetic capacity. GABA contributed to the root system architecture and the development of mature area of root tips. In addition, the intervention of exogenous GABA interfered with the homeostasis of endogenous IAA and activated the expression of P starvation induction (PSI) gene, leading to the significantly increase of the P uptake in apple plants. Meanwhile, transgenic roots with overexpressing MdGAD1 enhanced the tolerance of apple seedlings to low P stress, improved the root development through regulating IAA signaling pathway, and significantly improved the P uptake of apple seedlings under low P conditions. Conclusion: All results suggested that GABA could contribute to the adaption of apple seedlings to low P conditions, by decreasing ROS accumulation, maintaining photosynthetic capacity, and increasing IAA level to improve the root development and the P absorption. [ABSTRACT FROM AUTHOR]

Phosphorus is an important macronutrient for plant growth and is acquired by plants mainly as phosphate. Phosphate fertilizer is usually used to reduce inorganic phosphate (Pi) deficiency in the soil, improve the low phosphorus and drought tolerance of plants, and promote plant growth. Phosphate transporters (PHTs) play an important role in absorbing phosphorus from the soil. MdPHT1;7 was induced by Pi deficiency and drought in roots in our previous research. In this study, we cloned MdPHT1;7 and showed its heterologous expression can complement a high-affinity Pi transporter gene in the Pi uptake-defective yeast mutant BY4743. MdPHT1;7 is a phosphorus transporter located on the cell membrane. Overexpression of MdPHT1;7 in 'Orin' apple and 'Micro-Tom' tomato enhanced Pi accumulation, low Pi tolerance and drought tolerance. We hypothesized that MdPHT1;7 can enhance Pi absorption and play an important role in improving plant resistance to low phosphorus and drought stresses. [ABSTRACT FROM AUTHOR]

Aims: Salinity plays a crucial role in numerous environmental processes, with extreme concentrations resulting in the serious decline of global agricultural productivity. Plant-specific HD-Zip I transcription factors (TFs), particularly γ-clade HD-Zip I members, are key for the adaption of plants to various abiotic stresses. Our main purpose is to characterize the function of γ-clade HD-Zip I members in apple under salt stress. Methods: GL-3 and transgenic plants were grown in a hydroponic system or in soil and exposed to the presence or absence of NaCl. Photosynthetic capacity, root damage, Na+ and K+ accumulation, reactive oxygen species (ROS) accumulation, and RNA-seq were investigated. Results: MdHB-7 (γ-clade HD-Zip I TF) expression was induced by salt stress, particularly in the roots. We employed MdHB-7 overexpression and MdHB-7 RNAi transgenic apple plants for the treatments to explore the functions of MdHB-7 under salt stress. Results from the salt treatment and phenotypic evaluation revealed the enhancement of the salt tolerance of apple plants by the MdHB-7 expression. The overexpression of MdHB-7 reduced the salt stress-induced damage to root growth and vitality and maintained ion homeostasis. Moreover, the overexpression of MdHB-7 was observed to promote the detoxification of ROS. Transcriptome and qRT-PCR analysis demonstrate that MdHB-7 overexpression up-regulated the expression of antioxidant enzyme-related genes. MdHB-7-mediated root vitality, antioxidant activity and ion homeostasis were impaired, resulting in MdHB-7 RNAi lines that were more sensitive to salt stress. Conclusions: Our results demonstrate the key role of MdHB-7 as a salinity stress tolerance regulator in apple (Malus domestica). [ABSTRACT FROM AUTHOR]

Key message: Ionic imbalance is one adaptive strategy of kiwifruit to bicarbonate, as indicated mainly by NH4+ accumulation and increased NH4+/NO3− in bicarbonate-treated roots as well as decreased NH4+/NO3− in bicarbonate-treated leaves. Bicarbonate-induced leaf chlorosis is frequently observed in kiwifruit orchards. A time-course experiment was conducted to investigate the effects of bicarbonate stress on the growth, root acidification, and organic acid and nutrient concentrations of kiwifruit plants treated for 7, 14, 21, 28, and 42 days in hydroponics. After 21 days of bicarbonate treatment, the kiwifruit vines exhibited leaf chlorosis, as indicated by decreased SPAD, chlorophyll a and b as well as carotenoid. Moreover, bicarbonate treatment induced NH4+ accumulation and NO3− reduction in roots from day 21 onward, thereby increasing the ratio of NH4+ to NO3− in roots, and the opposite was true for leaves that seemed to respond to bicarbonate earlier than roots but in an inconsistent manner. Before leaf chlorosis, bicarbonate imposition induced succinic acid accumulation and K reduction in roots from day 14 onward. However, the K concentration increased in bicarbonate-treated leaves from day 28 onward. Bicarbonate treatment also reduced P in all plant parts and Fe in leaves from day 21 onward, lowered Zn and enhanced Ca and Mg in roots from day 28 onward. In addition, bicarbonate treatment increased citric acid and ferric chelate reductase (FCR) activity in roots at days 7 and 14, but decreased citric acid and H+ extrusion at day 28 and decreased FCR activity at day 42, respectively, indicating that root acidification is duration dependent. These results suggest that, except for succinic acid accumulation, ionic imbalance in the whole kiwifruit plants (particularly N form's shift) might be an alternative strategy to adapt to bicarbonate stress. [ABSTRACT FROM AUTHOR]

Melatonin (MT) modulates a wide range of physiological functions with pleiotropic effects in plants. In this study, we studied the effect of exogenous applications of MT to pear trees on indicators of pear fruit quality. The results showed that MT increased the size of pear fruit by improving the net photosynthetic rate and maximal quantum efficiency of photosystem II photochemistry during the late stage of pear fruit development. Overall, MT increased fruit weight by 47.85% compared to the control. During the period of fruit maturation, MT increased the content of soluble sugars, particularly sucrose and sorbitol, likely as a result of improved starch accumulation. Expression levels of the invertase gene Pbinvertase 1/2 were lower in MT-treated fruit that resulted in lower enzyme activity, whereas activity of sucrose phosphate synthase was greater due to enhanced levels of expression of PbSPS1/2/3. Thus, application of melatonin improved sucrose content. This study shows that the application of MT to pear trees may be utilized for the production of larger and sweeter fruit of higher economic value. [ABSTRACT FROM AUTHOR]

Background and aims: Malus prunifolia (Chinese name: Fu Ping Qiu Zi), a wild relative of cultivated apple (Malus x domestica Borkh), is extremely resistant to drought compared with domesticated cultivars, such as 'Golden Delicious'. However, the molecular mechanisms underlying drought resistance of M. prunifolia have not been characterized. This study investigates a new regulatory mechanism to improve apple drought resistance. Methods: M. prunifolia and 'Golden Delicious' were each grafted on M. hupehensis for gene expression analysis. The methylation level of the DREB2A promoter was determined by bisulfite sequencing and ChIP-qPCR. Chromatin immunoprecipitation sequencing (ChIP-seq) was used to identify target genes of MpDREB2A in apple. Results: The exposure to drought stress stimulated the expression level of DREB2A gene more than 100-fold in M. prunifolia, but only 16-fold in 'Golden Delicious'. This difference in gene expression could not be explained in terms of difference in leaf relative water content. Correspondingly, the methylation level of M. prunifolia DREB2A (MpDREB2A) promoter region was significantly reduced. Additionally, MpDREB2A conferred enhanced drought resistance when ectopically expressed in Arabidopsis. Over 2800 potential downstream target genes of MpDREB2A were identified by ChIP-seq and these downstream genes have diverse potential functions related to stress resistance. Conclusions: Methylation regulation in promoter of MpDREB2A may contribute to the drought resistance of M. prunifolia. [ABSTRACT FROM AUTHOR]

Quercetin and its glycoside derivatives were identified and quantified using high-performance liquid chromatograph (HPLC) and liquid chromatograph/mass spectrometer/mass spectrometer (LC/MS/MS) in the leaves, flowers, and fruits of 22 Malus genotypes. In all genotypes, small amounts of quercetin aglycone were present, with water-soluble glycoside forms were the most abundant in different Malus plant tissues, including quercetin-3-galactoside, quercetin-3-rutinoside, quercetin-3-glucoside, quercetin-3-xyloside, quercetin-3-arabinoside, and quercetin-3-rhamnoside. Among these six quercetin glycosides, quercetin-3-galactoside was the common form in Malus plants, except in the leaves and flowers of M. ceracifolia and M. magdeburgensis, and in the fruits of M. micromalus 'Haihong Fruit', where there was a higher concentration of quercetin-3-glucoside. Among the different tissues tested, leaves contained the highest concentration of quercetin and its glycosides, while fruits contained the lowest concentrations of these compounds. Among the genotypes we analyzed, no specific genotype consistently contained the highest concentration of quercetin and its glycoside derivatives. M. domestica 'Honeycrisp' had the highest total compound concentration (approximately 1600 mg kg−1), whereas M. hupehensis contained the lowest in its fruits. In contrast, the concentration of total quercetin and its glycosides was more than 5000 mg kg−1 in the leaves of eight genotypes and greater than 2500 mg kg−1 in the flowers of seven species. In general, the concentration of quercetin and its glycoside derivatives depended on the species and tissue type. These results may provide useful information for the evaluation and selection of edible Malus fruits and the materials for quercetin glycoside extraction. [ABSTRACT FROM AUTHOR]

The red coloration of young crabapple ( Malus orientalis) flowers results from their high cellular concentration of anthocyanins. As the petals grow larger, the color fades, which is commonly regarded as being caused by floral tissue expansion diluting the anthocyanin levels in larger cells. We hypothesized that the anthocyanins are degraded due to hydrogen peroxide (HO) and that the concentrations of each phenolic intermediate depends on the physiological growth of flower petals. A high-performance liquid chromatography (HPLC) analysis was performed to characterize the identities and concentrations of the diverse array of phenolics present during different growth stages in the crabapple flowers. The concentrations of gallic acid, caffeic acid, syringic acid, chlorogenic acid, phloridzin, procyanidin B1, procyanidin B2, and catechin significantly increased throughout development, while epicatechin and cyanidin-3-galactoside levels declined. Most flavonols (quercetin-3-xyloside, quercetin-3-rhaminose, quercetin-3-glucoside, and quercetin-3-arabinoside) increased until the fourth stage, after which they declined suddenly. Likewise, cyanidin-3-galactoside degraded sharply at stage III, exhibiting reciprocal relationship with HO concentration. Our results suggest that the concentrations of phenolic compounds are congruent with their functional activities in floral tissues, and that their systematic fluctuation mainly depends on environmental cues and physiological imbalances, not merely petal expansion. The results of this study will be useful for better understanding the physiological changes in phenolic content and anthocyanin degradation that occur during flower development. [ABSTRACT FROM AUTHOR]

Branch bending has been practiced for decades in China to induce flower buds in 'Fuji' apple. However, the optimum bending angle is yet to be elucidated. The main objectives of this study were to compare the effect of branch bending angles (70°, 90° and 110°) on the flowering and nutrient accumulation of 1-year-old shoots of 'Fuji' and 'Gala' apples and to determine the optimum branch bending angle for each cultivar. In both cultivars, the production of spurs and terminal flower buds, and the total sugar concentration and the carbon-to-nitrogen (C/N) ratio in the shoot terminals increased, whereas the N concentration decreased with increasing bending angles. The nutrient concentration was significantly higher in spurs than in medium and long shoots. The distinction between the changing patterns of C and N concentrations in the bent shoots during the growing season in our study suggested the competition of these two nutrients caused by vegetative and reproductive growth at different growing times. In 'Fuji' apple, the proportion of flowering buds appeared to increase more rapidly with the increase of bending angle from 70° to 110° than that in 'Gala' apple, and particularly a higher proportion of spurs was observed on 'Fuji' branches bent at a larger angle. The increase in the total sugar concentration and the C/N ratio in the shoot terminals of the bent branches might be involved in inducing floral buds after bending. The optimum bending angle was about 90° for 'Gala' apple and 110° for 'Fuji' apple, respectively. Bending could help farmers to reduce the severity of biennial fruiting in 'Fuji' apple. [ABSTRACT FROM AUTHOR]

Plants are often subjected to unfavorable growing conditions, such as a limited supply of nutrients. Macroautophagy (autophagy) is an intracellular recycling process that targets unwanted proteins or damaged organelles, thus providing the nitrogen and carbon needed for survival and new plant growth during different phases of development and nutrient deprivation. During the formation of autophagosomes, AuTophaGy-related protein 7 (ATG7) is involved in both the ATG8 and ATG12 conjugation pathways. We isolated two ATG7 orthologs- MdATG7a and MdATG7b-from 'Golden Delicious' apple ( Malus domestica Borkh.). Both were differentially responsive to leaf senescence, nitrogen depletion, and oxidative stresses at the transcriptional level. Heterologous expression of MdATG7b in Arabidopsis accelerated vegetative growth and facilitated the transition into reproductive phase, while also increasing the number of lateral branches, alleviating the negative effects of salt stress on seed germination and conferring tolerance to nitrogen- and carbon starvation. These results suggest that, as one of the important autophagy-related genes, MdATG7b enhances plant tolerance to nitrogen and carbon limitations, and it might be used as an important candidate for breeding crops with improved tolerance to nutrient-starvation stress. [ABSTRACT FROM AUTHOR]

Cystatins, or phytocystatins (PhyCys), comprise a family of plant-specific inhibitors of cysteine proteinases. They are thought to help regulate endogenous processes and protect plants against biotic or abiotic stresses, such as heat, salinity, cold, water deficit, chilling, and abscisic acid (ABA) treatment. We isolated and identified a novel cystatin gene from Malus prunifolia, MpCYS5. Its expression was typically induced by salt stress treatment; ectopic expression in Arabidopsis enhanced salt tolerance. Physiological parameters confirmed this phenotype, with the transgenics having remarkably lower electrolyte leakage (EL) values, higher chlorophyll concentrations, and lower levels of malondialdehyde (MDA) upon salt treatment. In addition, the accumulation of reactive oxygen species was markedly regulated by MpCYS5 under stress conditions, as shown by fluctuations in the concentrations of hydrogen peroxide and superoxide radicals and the activities of antioxidant enzymes. We also noted that this gene modulated tunicamycin (TM)-induced endoplasmic reticulum (ER) stress tolerance and functioned in the unfolded protein response (UPR)-signaling pathway in Arabidopsis. This was confirmed by the expression of eight ER stress-responsive genes. All marker genes examined were strongly induced in the wild type, while most of them maintained relatively stable over time in the transgenics. These results demonstrated that ectopic expression of a cystatin gene is associated with salt-tolerant and TM-tolerant phenotypes. Therefore, the discovery of MpCYS5 from M. prunifolia might establish a molecular link between the ER stress response and salt tolerance in plants. [ABSTRACT FROM AUTHOR]

Cystatins, or phytocystatins, are plant-specific inhibitors of cysteine proteinases that help regulate endogenous processes and protect plants against heat, salinity, cold, water deficits, chilling, and abscisic acid treatment. MpCYS2, a cystatin gene from Malus prunifolia, localized to the nucleus, cytoplasm, and plasma membrane in onion epidermal cells. Controlled by the 35S promoter, its ectopic expression in transgenic Arabidopsis lines caused accelerated seed germination and greater seedling growth when plants were exposed to osmotic or oxidative stress. Expression by this gene was also associated with enhanced drought tolerance in those transgenics. This positive response was manifested by changes measured in electrolyte leakage, the chlorophyll concentration, and malondialdehyde accumulations. Production of reactive oxygen species (ROS) was appreciably decreased in the dehydration-treated transgenic lines. This gene also influenced root hair development under osmotic-stress conditions. Our findings indicate that MpCYS2 affects the growth and tolerance of drought-stressed Arabidopsis plants possibly because of its influence on ROS accumulations and root hair formation. [ABSTRACT FROM AUTHOR]

Glycine-rich RNA-binding proteins (GR-RBPs) are involved in the post-transcriptional regulation of genes. Although they are known to have roles in plant responses to environmental stresses, their functions in diverse species under stress conditions are still unverified. We assessed the biological roles of MpGR- RBP1, a GR-RBP from Malus prunifolia that is up-regulated by salinity, oxidation, or abscisic acid. Under control of the 35S promoter, its ectopic expression in Arabidopsis resulted in accelerated seed germination and seedling growth in two transgenic lines when plants were exposed to high salt or oxidative stress. This gene also contributed to the enhancement of salt tolerance in transgenic Arabidopsis plants. Consistently, the enhanced tolerance was confirmed by the changes of physiological parameters including electrolyte leakage, chlorophyll concentration and malondialdehyde accumulation. The accumulation of reactive oxygen species (ROS) in the transgenics was appreciably decreased under salt stress. In addition, MpGR- RBP1 had an effect on stomatal closure under saline conditions. Taken together, these results demonstrate that MpGR- RBP1 affects the growth and tolerance of salt-stressed Arabidopsis plants. Its functioning may be due, in part, to its influence on ROS accumulation and stomatal behavior, thereby leading to improved salt tolerance. [ABSTRACT FROM AUTHOR]

Main conclusion: Solar ultraviolet irradiation regulates anthocyanin synthesis in apple peel by modulating the production of reactive oxygen species via plasma membrane NADPH oxidase instead of other pathways. The synthesis of anthocyanin in apple peels is dependent upon solar irradiation. Using 3-mm commercial glass to attenuate solar UV-A and UV-B light, we confirmed that solar UV irradiation regulated anthocyanin synthesis in apple peels after exposing previously bagged fruit to sunlight. During sunlight exposure, UV attenuation did not affect the expression of MdHY5, MdCOP1, or MdCRY2, but significantly lowered plasma membrane NADPH oxidase activity and superoxide anion concentrations. UV attenuation also reduced the expression levels of MdMYB10, MdPAL, MdCHS, MdF3H, MdDFR, MdANS and MdUFGT1, UDP-glycose:flavonoid 3-O-glycosyltransferase (UFGT) activity, and local concentrations of anthocyanin and quercetin-3-glycoside. In contrast, exogenous application of hydrogen peroxide could enhance anthocyanin and quercetin-3-glycoside synthesis. Xanthophyll cycle pool size on a chlorophyll basis was higher but its de-epoxidation was lower under direct sunlight irradiation than that under UV-attenuating conditions. This suggests that reactive oxygen species (ROS) produced in chloroplast are not major contributors to anthocyanin synthesis regulation. Inhibition of plasma membrane NADPH oxidase activity lowered the production of ROS through this mechanism, significantly inhibited the synthesis of anthocyanin, and increased the total production of ROS in apple peel under direct sunlight irradiation, suggesting that ROS produced via plasma membrane NADPH oxidase regulates anthocyanin synthesis. In summary, solar UV irradiation regulated anthocyanin synthesis in apple peels by modulating the production of ROS via plasma membrane NADPH oxidase. [ABSTRACT FROM AUTHOR]

There is now biochemical and genetic evidence that oxidative cleavage of cis-epoxycarotenoids by 9- cis-epoxycarotenoid dioxygenase (NCED) is the critical step in the regulation of abscisic acid (ABA) synthesis in higher plants. To understand the expression characteristics of NCED during ABA biosynthesis in apple ( Malus), two NCED genes cDNA sequence were cloned from Malus prunifolia using RT-PCR techniques, named MpNCED1 and MpNCED2. The two cDNA sequences have full-length open reading frame, encoding a polypeptide of 607 and 614 amino acids, respectively. Sequences analysis showed that the deduced two apple NCED proteins were highly homologous to other NCED proteins from different plant species. Real-time PCR analysis revealed MpNCED2 were expressed continuously during the whole period of apple fruit development with the pattern of 'higher-low-highest', while the expression of MpNCED1 clearly declined to a steady low level in the mid-later period of fruit development. Expression of the MpNCED2 increased under the drought stress, high temperature and low temperature strongly and rapidly, whereas expression of the MpNCED1 was detected in response to temperature stress, but did not detected under drought stress. These results revealed that MpNCED1 and MpNCED2 may play different roles in regulation of the ABA biosynthesis in fruit development and various stresses response. [ABSTRACT FROM AUTHOR]

Apple ( Malus domestica) rootstock G.41 is an excellent member of the Geneva series because it has traits for resistance to abiotic and biotic stresses. A simple and efficient protocol for obtaining shoots from leaf explants was established by optimizing the combinations of plant growth regulators, mode of wounding, and explant orientation on the culture medium. The best shoot multiplication index (2.58) was obtained from successful subculture medium that was the standard Murashige and Skoog (MS) medium supplemented with 7.5 g L agar, 3.55 μM N-benzyladenine, 0.16 μM indole-3-butyric acid, and 30 g L sucrose. Regeneration rates were highest (99%) when MS medium was supplemented with 2.7 μM thidiazuron and 0.9 μM 1-naphthaleneacetic acid, and cut-wounding explants before placing the abaxial surface in contact with the medium. The best rooting percentage (80%) was obtained on MS medium supplemented with 4.92 μM indole-3-butyric acid. Plantlets were rooted in vitro and survived acclimatization in the laboratory and greenhouse. [ABSTRACT FROM AUTHOR]

The dehydration responsive element-binding (DREB) proteins play a critical role in plant development and abiotic stress-mediated gene expression. Therefore, they represent one of the most attractive regulons for breeding programs. However, no comprehensive summary of grapevine DREB family genes is available. During this study, 38 VvDREB members were identified from the entire grapevine genome and its expression sequence tag assembly. These were organized into the same subgroups, A1 through A6, as for Arabidopsis DREBs. The VvDREB genes were distributed in 15 out of 19 chromosomes in grapevine. Multiple sequence alignments were performed and a three-dimensional structure was created to demonstrate sequence conservation. Microarray analysis showed potential regulatory roles for VvDREBs in responses to various abiotic stresses, hormone treatments, berry ripening, exposure to light, and bud development. Cis-acting regulatory elements, such as W-box, MYB-binding site, and light-responsive elements, were the most frequently found in the putative promoter regions. Furthermore, microarray transcriptional profiling of grapevine plants that over-expressed VvDREB23 revealed 248 up-regulated and 229 down-regulated genes, with fold-changes of >1.5 when compared with the empty vector control. Gene ontology classifications showed that different genes function in cellular glucan metabolism, lipid transport, the endomembrane system, cell wall structure, and other important metabolic and developmental processes, as well as in the regulation of molecular functions. Our report provides an overview and constitutes a foundation for further study of this VvDREB gene family. All the microarray data and transcription profiling of transgenic versus empty-vector control transformant grapevines were retrieved from the online resources. [ABSTRACT FROM AUTHOR]

Ascorbic acid (AsA) plays an essential role in plants by protecting cells against oxidative damage. GDP- l-galactose phosphorylase ( GGP) is the first committed gene for AsA synthesis. Our research examined AsA levels, regulation of GGP gene expression, and how these are related to abiotic stresses in two species of Actinidia (kiwifruit). When leaves were subjected to continuous darkness or light, ABA or MeJA, heat, or a hypoxic environment, we found some correlation between the relative levels of GGP mRNA and AsA concentrations. In transformed tobacco plants, activity of the GGP promoter was induced by all of these treatments. However, the degree of inducibility in the two kiwifruit species differed among the GGP promoter deletions. We deduced that the G-box motif, a light-responsive element, may have an important function in regulating GGP transcripts under various light conditions in both A. deliciosa and A. eriantha. Other elements such as ABRE, the CGTCA motif, and HSE might also control the promoter activities of GGP in kiwifruit. Altogether, these data suggest that GGP expression in the two kiwifruit species is regulated by light or abiotic stress via the relative cis-elements in their promoters. Furthermore, GGP has a critical role in modulating AsA concentrations in kiwifruit species under abiotic stresses. [ABSTRACT FROM AUTHOR]

Marssonina apple blotch, caused by Diplocarpon mali (anamorph: Marssonina coronaria), is a serious disease of apple ( Malus x domestica Borkh.). We evaluated the resistance of 28 cultivars and 39 species or biotypes after inoculating leaves with conidial suspensions in vitro and in vivo. Five accessions of the 28 apple cultivars showed a good level of resistance, while 16 displayed intermediate type. In contrast, resistance was good for eight accessions of species or biotypes and moderate for 19 accessions. Among these 67 candidates, more than 19 % had resistance against Marssonina apple blotch, indicating that resistant resources are abundant in that germplasm. These high-performing accessions can make valuable contributions to breeding programs for resistance against this disease. [ABSTRACT FROM AUTHOR]

Aquaporins play an essential role in regulating the water balance in plants. We compared responses between Malus prunifolia (Willd.) Borkh., a reputedly drought-tolerant rootstock, and M. hupehensis Pamp. Reld., which is drought-sensitive. One-year-old seedlings were treated with long-term, moderate water deficit (field capacity of 45-50 %), and were monitored for photosynthetic characteristics, leaf relative water content (LRWC). The relative expressions of mRNA encoding six putative aquaporins also were determined by Q-RT-PCR. Throughout the experimental period, M. prunifolia had higher readings for all four photosynthetic characteristics. Values for LRWC were rapidly reduced under stress, especially for M. hupehensis. Except for TIP2;1, the transcript abundance of most aquaporin genes was elevated after drought stress, reaching a peak at Day 14 before declining in the leaves and roots of both species. For TIP2;1, however, the transcript level was continuously reduced in M. prunifolia leaves throughout the entire course of treatment. Expression of aquaporin genes varied according to the gene, water status, and plant organ being examined. We conclude that Malus aquaporins are responsive to water stress at the transcriptional level, probably playing several roles in conferring drought tolerance. Ours is the first report of this relationship between aquaporins and drought tolerance in Malus species. [ABSTRACT FROM AUTHOR]

The gene encoding l-galactose-1-phosphate phosphatase ( GPP) plays a central role in ascorbic acid (AsA) biosynthesis in plants. Here, we report AsA contents, GPP expression, and functioning of its promoter in response to light, exogenous stress-signalling hormones, or abiotic stresses in kiwifruit ( Actinidia deliciosa). To identify the upstream region of GPP required for promoter activity, we constructed a series of promoter deletion derivatives. Each construct was analyzed by Agrobacterium-mediated transient transformation in tobacco leaves after various treatments. Some correlation was observed between the relative levels of GPP mRNA and AsA contents when kiwi leaves were exposed to varying light conditions, treatment with ABA or SA, wounding, or a hypoxic environment. Analysis of a series of 5′ deletions in tobacco leaves indicated that the proximal area 390 bp from the transcription initiation site was needed for establishing both the constitutive and the induced patterns of expression. This promoter was induced by light or one of our abiotic treatments. These results suggest that GPP is regulated by light or abiotic stress and that it plays an important role in controlling AsA contents in kiwifruit. [ABSTRACT FROM AUTHOR]

Malus prunifolia is an important germplasm resource for apple rootstock. However, no comprehensive and systematic evaluation has been made of its salt tolerance. We compared salt injury (SI), net photosynthetic rate (Pn), variation percentage (VP) of electrolyte leakage (EL), relative water content (RWC) and adverse resistance coefficients (ARC) in nine biotypes of Malus prunifolia when plants were exposed to 150 mM NaCl for 10 days. Two other valuable rootstock sources ( M. sieversii and M. hupehensis) were also analyzed. Under high-salinity conditions, all growth parameters except EL were significantly decreased compared with the untreated control. The greatest changes were found with Pn. Values for RWC and ARC also declined under saline treatment, although the extent of that decrease varied among biotypes. Based on our results for SI, as well as ARC and cluster analysis, we deemed these biotypes to be salt-tolerant: M. prunifolia 'fupingqiuzi', M. prunifolia 'dongbeihuanghaitang', M. prunifolia 'laoshannaizi', M. sieversii, and M. hupehensis. By contrast, M. prunifolia 'baihaitang', M. prunifolia 'wulenghaitang' and M. prunifolia 'neimengguhaihong' proved to be salt-sensitive. [ABSTRACT FROM AUTHOR]

l- myo-inositol-1-phosphate synthase (MIPS; EC 5.5.1.4) is the key enzyme involved in de novo synthesis of myo-inositol, leading to numerous cellular functions. We isolated an open reading frame of Actinidia deliciosa MIPS ( AdMIPS), which is 1,533 bp long and codes for 510 amino acids, with a predicted molecular weight of 56.3 kDa. Sequence analysis revealed its high similarity with MIPS proteins from other organisms. Gene expression and enzyme activity were highest in flower and young fruit. Transcription of AdMIPS was also detected in other tissues. Moderate drought drastically induced expression in the leaves whereas salinity stress induced transcription and enzyme activity in the leaves, phloem, and roots with different degrees. However, a longer period of saline exposure suppressed both expression and enzyme activity in all sampled tissues, indicating that AdMIPS is salt-sensitive. [ABSTRACT FROM AUTHOR]

The family of dehydrin genes has important roles in protecting higher plants against abiotic stress, such as drought, salinity and cold. However, knowledge about apple dehydrin gene family is limited. In the present study, we used a bioinformatics approach to identify members of that family in apple ( Malus domestica). A total of 12 apple dehydrin genes ( MdDHNs) were identified and located on various chromosomes. All putative proteins from those genes contained a typical K domain. Among 12 MdDHNs, nine were cloned and their expression patterns were investigated. Expression profiling indicated that the these nine dehydrin genes display differential expression patterns in various tissues. Moreover, transcript levels of some MdDHNs were up-regulated significantly under drought, low temperature, or ABA treatment, which indicated their important roles during stress adaptation. These results demonstrate that the apple dehydrin gene family may function in tissue development and plant stress responses. [ABSTRACT FROM AUTHOR]

Grafting rootstocks are widely used to enhance plants resistance to various biologic and abiotic stresses. We determined how the rootstock genotype might influence plant responses to drought, using 2-year-old 'Gale Gala' apple trees grafted onto Malus sieversii and M. hupehensis. Under water stress, trees with the former as their rootstock had smaller reductions in rates of relative growth and photosynthesis, total biomass, leaf area, levels of leaf chlorophyll, and relative water content compared with those grafted onto the latter. They also had greater maximum photochemical efficiency and water-use efficiency. On the other hand, trees growing on M. sieversii rootstock had less production of superoxide radicals and hydrogen peroxide in both leaves and roots than those growing on M. hupehensis in response to drought stress. Furthermore, under drought conditions, leaves and roots from trees grafted onto M. sieversii had greater synthesis of ascorbic acid and glutathione, as well as higher activities of superoxide dismutase, catalase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase. These results suggest that the choice of grafting rootstock can enhance drought resistance by improving the antioxidant system in a plant. Here, 'Gale Gala' trees grafted onto M. sieversii were more drought-resistant than those on M. hupehensis rootstock. [ABSTRACT FROM AUTHOR]

The dehydration responsive element binding (DREB) transcription factor family is one of the most promising regulons for genetic engineering of plant responses to abiotic stresses. However, knowledge about apple DREB genes is limited. In the present study, we found, for the first time, 68 MdDREB genes that could be further classified into six subgroups against the entire genome of apple. All putative proteins from those genes contained a typical APETALA 2 domain and shared similar motifs. The predicted MdDREBs were distributed with different densities over 12 chromosomes, with five tandem duplication sites occurring simultaneously. Both Genevestigator and expressed sequence tags were used for preliminary investigations of expression patterns. Results from quantitative real-time PCR showed that transcript levels of some putative MdDREB genes were up-regulated significantly under various abiotic-stress treatments, which indicated their vital roles during stress adaptation. Identifying these genes and profiling their expression provides useful information and constitutes a foundation for their further, practical utilization in apple through gene-transfer techniques. [ABSTRACT FROM AUTHOR]

Members of the plant glycine-rich RNA-binding protein (GR-RBP) family play diverse roles in regulating RNA metabolism for various cellular processes. To understand better their function at the molecular level in stress responses, we cloned a GR-RBP gene, MhGR- RBP1, from Malus hupehensis. Its full-length cDNA is 558 bp long, with a 495-bp open reading frame, and it encodes 164 amino acids. The deduced amino acid sequence contains an RNA-recognition motif (RRM) at the amino terminal and a glycine-rich domain at the carboxyl terminal; these are highly homologous with those from other plant species. Multiple alignment and phylogenetic analyses show that the deduced protein is a novel member of the plant GR-RBP family. To characterize this gene, we also applied a model for predicting its homology of protein structure with other species. Both organ-specific and stress-related expression were detected by quantitative real-time PCR and semi-quantitative RT-PCR, indicating that MhGR- RBP1 is expressed abundantly in young leaves but weakly in roots and shoots. Transcript levels in the leaves were increased markedly by drought, hydrogen peroxide (HO), and mechanical wounding, slightly by salt stress. Furthermore, the transcript is initially up- and down-regulated rapidly within 24 h of abscisic acid (ABA) treatment. After 24 h of ABA and jasmonic acid (JA) treatments with different concentrations, the transcript levels of MhGR- RBP1 were significantly repressed. These results suggest that MhGR- RBP1 may be involved in the responses to abiotic stresses, HO, ABA, or JA. [ABSTRACT FROM AUTHOR]

In China, the native Lanzhou lily ( Lilium davidii var. unicolor) is used as an edible lily and is an important source of ascorbic acid. However, an efficient transformation system has not been developed for this important crop. Here, we describe the first successful genetic transformation mediated by particle bombardment in this lily variety. We used pCAMBIA-GLDH, which contains the l -galactono-1, 4-lactone dehydrogenase gene from apple, a hygromycin phosphotransferase gene as a selectable marker, and an intron-containing β-glucuronidase gene as a reporter. In all, 35 transgenic lines were selected via GUS assays and PCR; from these, eight were confirmed by Southern analyses. Transgenic plants were transferred to soil and grown under greenhouse conditions. The levels of reduced ascorbate and total ascorbate (reduced ascorbate + oxidized ascorbate) in transgenic plants were found to be two to seven times those in non-transgenic controls. [ABSTRACT FROM AUTHOR]

Plant growth, biomass allocation, carbon isotope composition (δC), and water use efficiency (WUE) of 31 cultivars of apple ( Malus domestica Borkh.) grown under two water regimes were measured. Drought-stressed plants showed significant declines in tree height, trunk diameter, biomass production, and total leaf area, the extent to which depended upon cultivar. Also, gas exchange rates, instantaneous and long-term efficiencies (WUE and WUE, respectively), and values for δC differed among cultivars and watering regimes. Variations in WUE were mainly due to changes in stomatal conductance ( g) under drought condition. 'Qinguan' and 'Golden Delicious' had greater trunk diameter, tree height, and had higher biomass production and WUE under drought stress, implying that they are more suitable for arid and semi-arid regions. Moreover, WUE was significantly and positively correlated with δC under two watering regimes, which suggests a potential for evaluating water use efficiency of Malus by measuring carbon isotope composition. [ABSTRACT FROM AUTHOR]

Plant hormones play important roles in regulating developmental processes and signaling networks involved in plant responses to biotic and abiotic stresses. We comparatively studied the growth and endogenous hormonal levels in leaves and roots in two Malus species ( M. sieversii and M. hupehensis) differing in hypoxia tolerance under normoxic and hypoxia stress. The results showed that hypoxia stress inhibited growth of seedlings of both Malus species, but with significant differences in intensity . Exposure to hypoxia altered the levels of endogenous hormones in leaves and roots in both Malus seedlings. Leaf and root abscisic acid (ABA) contents increased in response to hypoxia stress in both genotypes despite different extents. Compared with M. hupehensis, M. sieversii was more responsive to hypoxia stress, resulting in larger increases in leaf and root ABA contents. The changes in leaf and root ABA contents correlating with the different tolerance levels of the genotypes confirm the involvement of this hormone in plant responses to hypoxia stress. Gibberellins (GAs; GA + GA) continuously increased in leaves and roots during the whole period of stress, whereas indole-3-acetic acid (IAA) showed a sharp increase at the early stage in both Malus seedlings. In addition, zeatin riboside (ZR), dihydrozeatin riboside (DHZR), and isopentenyl adenine (IPA) differed in their pattern of changes in both Malus seedlings under hypoxia stress. Based on variations in endogenous hormonal levels in both Malus species that differ in their ability to tolerate hypoxia, we conclude that not a single hormone but multiple hormones and their interplay are responsible for hypoxia tolerance. [ABSTRACT FROM AUTHOR]

Drought is one of the most severe environmental factors that impair plant growth and agricultural production. To investigate how Malus prunifolia, an excellent apple rootstock with strong drought tolerance, adapts to stress and to identify genes for improving this important trait, we constructed a suppression subtractive hybridization cDNA library from seedling leaves under water stress. The cDNA for a drought-inducible glycine-rich RNA-binding protein (GR-RBP) was isolated, and the gene was characterized for its role in the response of Malus seedlings to drought stress. cDNA clone MpGR-RBP1 has 781 nucleotides, with an open reading frame of 516 nucleotides. The deduced 171 amino acids contain an amino-terminal RNA recognition motif and a carboxyl-terminal glycine-rich domain, with structural similarity to a class of stress-induced GR-RBP proteins found in other plants. Phylogenetic analysis confirmed that the MpGR-RBP1 protein belongs to the plant GR-RBP family, members of which play important roles in posttranscriptional regulation of gene expression under various stress conditions. The expression profile of MpGR-RBP1 transcripts was detected by quantitative real-time polymerase chain reaction (PCR) and semiquantitative reverse transcriptase PCR. MpGR-RBP1 was expressed in both roots and leaves, with expression being higher in the latter. This is the first report of this class of protein in Malus plants, and the putative role of MpGR-RBP1 is discussed. [ABSTRACT FROM AUTHOR]

Variations in biomass productivity, plant water-use efficiency (WUE), and carbon isotope composition (δC) were investigated among 10 Malus rootstocks. In the semi-controlled environmental of a greenhouse, plants were watered to either 75% or 50% of field capacity. For each treatment, significant differences were found in dry matter accumulation and allocation, δC, and WUE. Relative growth rate (RGR) was correlated with WUE but not with allocation pattern. Variations in whole-plant transpiration were a result of fluctuations in the rate of transpiration per unit leaf area rather than from differences in leaf area or root weight per plant. Values for transpiration per unit leaf area or root weight were lower when the proportion of either leaf area or root weight per unit plant weight was larger. Rootstock differences in δC were related to changes in stomatal conductance rather than in net photosynthesis. Finally, δC was significantly correlated with WUE and rootstock rankings based on both of those parameters were maintained regardless of watering treatment. [ABSTRACT FROM AUTHOR]

Soil salinity is a major factor limiting apple production in some areas. Tonoplast Na/H antiporters play a critical role in salt tolerance. Here, we isolated MdNHX1, a vacuolar Na/H antiporter from Luo-2, a salt-tolerant rootstock of apple ( Malus × domestica Borkh.), and introduced it into apple rootstock M.26 by Agrobacterium-mediated transformation. PCR and DNA gel blot analyses confirmed successful integration of MdNHX1. RT-PCR analysis indicated that the gene was highly expressed in transgenic plants, but the degree of this expression varied among lines. Its overexpression conferred high tolerance to salt stress. Analysis of ion contents showed that, when exposed to salinity stress, the transgenics compartmentalized more Na in the roots and also maintained a relatively high K/Na ratio in the leaves compared with non-transformed plants. Under normal conditions, however, amounts of potassium and sodium did not differ significantly between transgenic and control plants. [ABSTRACT FROM AUTHOR]

Heat stress, which is caused by global warming, threatens crops yield and quality across the world. As a kind of post-translation modification, SUMOylation involves in plants heat stress response with a rapid and wide pattern. Here, we identified small ubiquitin modifiers (SUMO), which affect drought tolerance in apple, also participated in thermotolerance. Six isoforms of SUMOs located on six chromosomes in apple genome, and all the SUMOs were up-regulated in response to heat stress condition. The MdSUMO2 RNAi transgenic apple plants exhibited higher survival rate, lower ion leakage, higher catalase (CAT) activity, and Malondialdehyde (MDA) content under heat stress. MdDREB2A, the substrate of MdSUMO2 in apple, was accumulated in MdSUMO2 RNAi transgenic plants than the wild type GL-3 at the protein level in response to heat stress treatment. Further, the inhibited SUMOylation level of MdDREB2A in MdSUMO2 RNAi plants might repress its ubiquitination, too. The accumulated MdDREB2A in MdSUMO2 RNAi plants further induced heat-responsive genes expression to strengthen plants thermotolerance, including MdHSFA3, MdHSP26.5, MdHSP18.2, MdHSP70, MdCYP18-1 and MdTLP1. In summary, these findings illustrate that interfering small ubiquitin modifiers (SUMO) in apple improves plants thermotolerance, partly by facilitating the stability and activity of MdDREB2A., (© 2023. The Author(s).)

The deficient agricultural water caused by water shortage is a crucial limiting factor of horticultural production. Among many agricultural water-saving technologies, regulated deficit irrigation (RDI) has been proven to be one of the effective technologies to improve water use efficiency and reduce water waste on the premise of maintaining the quality of agricultural products. RDI was first reported more than 40 years ago, although it has been applied in some areas, little is known about understanding of the implementation method, scope of application and detailed mechanism of RDI, resulting in the failure to achieve the effect that RDI should have. This review refers to the research on RDI in different crops published in recent years, summarizes the definition, equipment condition, function, theory illumination, plant response and application in different crops of RDI, and looks forward to its prospect. We expect that this review will provide valuable guidance for researchers and producers concerned, and support the promotion of RDI in more horticultural crops., (© 2022. The Author(s).)

The wax layer of apple leaves plays an important role in improving stress resistance, but relatively little is known about the mechanisms of wax synthesis and transport in apple leaves. In this study, 17 wax components, including alcohols, alkanes, fatty acids and terpenes, were analyzed by gas chromatography-tandem mass spectrometry (GC-MS) from the leaves of 123 apple germplasms. Whole-genome sequencing of these apple accessions yielded 5.9 million high-quality single nucleotide polymorphisms (SNPs). We performed a genome-wide association study (GWAS) on 17 wax components and identified several genes related to wax synthesis and transport, including MdSHN1 (SHINE1), MdLTP4 (LIPID TRANSFER PROTEIN4), MdWSD1 (WAX ESTER SYNTHASE/ACYL-COA DIAC-YLGLYCEROL ACYLTRANSFERASE1), MdRDR1 (RNA-DEPENDENT RNA POLYMERASE1), MdACBP6 (ACYL-COA-BINDING PROTEIN6), MdNLE (NOTCHLESS) and MdABCG21 (ATP-BINDING CASSETTE G21). Moreover, we identified some prominent SNPs that may affect gene expression and protein function. These results provide insights into mechanisms of wax synthesis and transport in apple leaves and broaden the genetic resources and basis for facilitating resistance breeding., (© 2021. The Author(s).)