Molecular cloning and characterization of CrNCED1, a gene encoding 9-cis-epoxycarotenoid dioxygenase in Citrus reshni, with functions in tolerance to multiple abiotic stresses

Expression pattern of candidate genes and their correlation with various metabolites of abscisic acid biosynthetic pathway under drought stress in rice

Drought hampers global rice production. Abscisic acid (ABA) plays versatile roles under different environmental stresses. While the link between drought and ABA is known, its effect on ABA biosynthesis genes and metabolites is unclear. This study explored the impact of drought on various metabolites, namely beta-carotene, zeaxanthin, antheraxanthin, violaxanthin, neoxanthin, and candidate genes viz. zeaxanthin epoxidase (ZEP) and 9-cis epoxycarotenoid dioxygenase (NCED) of ABA biosynthesis pathway in rice cultivars (N22 and IR64) at anthesis {65 DAT (Days after transplanting)} with different stress levels. In stressed plants, zeaxanthin significantly increased (92%), while the concentration of beta-carotene, antheraxanthin, violaxanthin and neoxanthin decreased as drought stress progressed. The concentration of metabolites in roots was notably lower than in leaves in both genotypes. The ZEP expression was upregulated in roots (8.24-fold) under drought stress. Among five NCED isoforms, NCED3 showed significant upregulation (7.29-fold) in leaf and root tissue. NCED1 was significantly downregulated as stress progressed and was negatively correlated with ABA accumulation. NCED2, NCED4 and NCED5 showed no significant change in their expression. Drying and rolling of rice leaves was observed after imparting drought stress. The findings revealed that drought stress significantly influenced the expression of candidate genes and the concentration of metabolites of the ABA biosynthesis pathway. There was a significantly higher accumulation of ABA in N22 leaves (47%) and roots (30%) compared to IR64. The N22, a drought-tolerant genotype, exhibited significantly higher concentrations of intermediates and demonstrated increased expression of ZEP and NCED3, potentially contributing to its resilience against drought.

Genome-wide identification and in-silico expression analysis of carotenoid cleavage oxygenases gene family in Oryza sativa (rice) in response to abiotic stress

Rice constitutes a foundational cereal and plays a vital role in the culinary sector. However, the detriments of abiotic stress on rice quality and productivity are noteworthy. Carotenoid cleavage oxygenases (CCO) hold vital importance as they enable the particular breakdown of carotenoids and significantly contribute towards the growth and response to abiotic stress in rice. Due to the insufficient information regarding rice CCOs and their potential role in abiotic stress, their utilization in stress-resistant genetic breeding remains limited. The current research identified 16 CCO genes within the Oryza sativa japonica group. These OsCCO genes can be bifurcated into three categories based on their conserved sequences: NCEDs (9-Cis-epoxycarotenoid dioxygenases), CCDs (Carotenoid cleavage dioxygenases) and CCD-like (Carotenoid cleavage dioxygenases-like). Conserved motifs were found in the OsCCO gene sequence via MEME analysis and multiple sequence alignment. Stress-related cis-elements were detected in the promoter regions of OsCCOs genes, indicating their involvement in stress response. Additionally, the promoters of these genes had various components related to plant light, development, and hormone responsiveness, suggesting they may be responsive to plant hormones and involved in developmental processes. MicroRNAs play a pivotal role in the regulation of these 16 genes, underscoring their significance in rice gene regulation. Transcriptome data analysis suggests a tissue-specific expression pattern for rice CCOs. Only OsNCED6 and OsNCED10 significantly up-regulated during salt stress, as per RNA seq analyses. CCD7 and CCD8 levels were also higher in the CCD group during the inflorescence growth stage. This provides insight into the function of rice CCOs in abiotic stress response and identifies possible genes that could be beneficial for stress-resistant breeding.

Phylogeny of PmCCD Gene Family and Expression Analysis of Flower Coloration and Stress Response in Prunus mume

The CCD gene family plays a crucial role in the cleavage of carotenoids, converting them into apocarotenoids. This process not only impacts the physiology and development of plants but also enhances their tolerance toward different stresses. However, the character of the PmCCD gene family and its role in ornamental woody Prunus mume remain unclear. Here, ten non-redundant PmCCD genes were identified from the P. mume genome, and their physicochemical characteristics were predicted. According to the phylogenetic tree, PmCCD proteins were classified into six subfamilies: CCD1, CCD4, CCD7, CCD8, NCED and CCD-like. The same subfamily possessed similar gene structural patterns and numbers of conserved motifs. Ten PmCCD genes were concentrated on three chromosomes. PmCCD genes exhibited interspecific collinearity with P. armeniaca and P. persica. Additionally, PmCCD genes had obvious specificity in different tissues and varieties. Compared with white-flowered 'ZLE', PmCCD1 and PmCCD4 genes were low-expressed in 'HJH' with yellow petals, which suggested PmCCD1 and PmCCD4 might be related to the formation of yellow flowers in P. mume. Nine PmCCD genes could respond to NaCl or PEG treatments. These genes might play a crucial role in salt and drought resistance in P. mume. Moreover, PmVAR3 and PmSAT3/5 interacted with PmCCD4 protein in yeast and tobacco leaf cells. This study laid a foundation for exploring the role of the PmCCD gene family in flower coloration and stress response in P. mume.

The RNA-binding protein MdHYL1 modulates cold tolerance and disease resistance in apple

Apple (Malus domestica) trees often experience various abiotic and biotic stresses. However, due to the long juvenile period of apple and its high degree of genetic heterozygosity, only limited progress has been made in developing cold-hardy and disease-resistant cultivars through traditional approaches. Numerous studies reveal that biotechnology is a feasible approach to improve stress tolerance in woody perennial plants. HYPONASTIC LEAVES1 (HYL1), a double-stranded RNA-binding protein, is a key regulator involved in apple drought stress response. However, whether HYL1 participates in apple cold response and pathogen resistance remains unknown. In this study, we revealed that MdHYL1 plays a positive role in cold tolerance and pathogen resistance in apple. MdHYL1 acted upstream to positively regulate freezing tolerance and Alternaria alternata resistance by positively modulating transcripts of MdMYB88 and MdMYB124 in response to cold stress or A. alternata infection. In addition, MdHYL1 regulated the biogenesis of several miRNAs responsive to cold and A. alternata infection in apple. Furthermore, we identified Mdm-miRNA156 (Mdm-miR156) as a negative regulator of cold tolerance and Mdm-miRNA172 (Mdm-miR172) as a positive regulator of cold tolerance, and that Mdm-miRNA160 (Mdm-miR160) decreased plant resistance to infection by A. alternata. In summary, we highlight the molecular role of MdHYL1 regarding cold tolerance and A. alternata infection resistance, thereby providing candidate genes for breeding apple with freezing tolerance and A. alternata resistance using biotechnology.

Genome-Wide Identification and Expression Analysis of NCED Gene Family in Pear and Its Response to Exogenous Gibberellin and Paclobutrazol

The 9-cis-epoxycarotenoid dioxygenase (NCED) is a key enzyme for the process of ABA synthesis that plays key roles in a variety of biological processes. In the current investigation, genome-wide identification and comprehensive analysis of the NCED gene family in 'Kuerle Xiangli' (Pyrus sinkiangensis Yu) were conducted using the pear genomic sequence. In total, nineteen members of PbNCED genes were identified from the whole genome of pear, which are not evenly distributed over the scaffolds, and most of which were focussed in the chloroplasts. Sequence analysis of promoters showed many cis-regulatory elements, which presumably responded to phytohormones such as abscisic acid, auxin, etc. Synteny block indicated that the PbNCED genes have experienced strong purifying selection. Multiple sequence alignment demonstrated that these members are highly similar and conserved. In addition, we found that PbNCED genes were differentially expressed in various tissues, and three PbNCED genes (PbNCED1, PbNCED2, and PbNCED13) were differentially expressed in response to exogenous Gibberellin (GA₃) and Paclobutrazol (PP₃₃₃). PbNCED1 and PbNCED13 positively promote ABA synthesis in sepals after GA₃ and PP₃₃₃ treatment, whereas PbNCED2 positively regulated ABA synthesis in ovaries after GA₃ treatment, and PbNCED13 positively regulated ABA synthesis in the ovaries after PP₃₃₃ treatment. This study was the first genome-wide report of the pear NCED gene family, which could improve our understanding of pear NCED proteins and provide a solid foundation for future cloning and functional analyses of this gene family. Meanwhile, our results also give a better understanding of the important genes and regulation pathways related to calyx abscission in 'Kuerle Xiangli'.

SiNCED1, a 9-cis-epoxycarotenoid dioxygenase gene in Setaria italica, is involved in drought tolerance and seed germination in transgenic Arabidopsis

Foxtail millet (Setaria italica L.) is a vital cereal food crop with promising development and utilization potential because of its outstanding ability to resist drought stress. However, the molecular mechanisms underlying its drought stress resistance remain unclear. In this study, we aimed to elucidate the molecular function of a 9-cis-epoxycarotenoid dioxygenase gene, SiNCED1, in the drought stress response of foxtail millet. Expression pattern analysis showed that SiNCED1 expression was significantly induced by abscisic acid (ABA), osmotic stress, and salt stress. Furthermore, ectopic overexpression of SiNCED1 could enhance drought stress resistance by elevating endogenous ABA levels and promoting stomatal closure. Transcript analysis indicated that SiNCED1 modulated ABA-related stress responsive gene expression. In addition, we found that ectopic expression of SiNCED1 delayed seed germination under normal and abiotic stress conditions. Taken together, our results show that SiNCED1 plays a positive role in the drought tolerance and seed dormancy of foxtail millet by modulating ABA biosynthesis. In conclusion, this study revealed that SiNCED1 is an important candidate gene for the improvement of drought stress tolerance in foxtail millet and could be beneficial in the breeding and investigation of drought tolerance in other agronomic crops.

Modifications of Phytohormone Metabolism Aimed at Stimulation of Plant Growth, Improving Their Productivity and Tolerance to Abiotic and Biotic Stress Factors

Due to the growing human population, the increase in crop yield is an important challenge for modern agriculture. As abiotic and biotic stresses cause severe losses in agriculture, it is also crucial to obtain varieties that are more tolerant to these factors. In the past, traditional breeding methods were used to obtain new varieties displaying demanded traits. Nowadays, genetic engineering is another available tool. An important direction of the research on genetically modified plants concerns the modification of phytohormone metabolism. This review summarizes the state-of-the-art research concerning the modulation of phytohormone content aimed at the stimulation of plant growth and the improvement of stress tolerance. It aims to provide a useful basis for developing new strategies for crop yield improvement by genetic engineering of phytohormone metabolism.

Molecular and Enzymatic Characterization of 9-Cis-epoxycarotenoid Dioxygenases from Mulberry

Abscisic acid (ABA) is involved in many physiological regulatory processes in plants, such as leaf shedding, stomatal closure, inhibition of cell elongation, as well as responses to multi-abiotic stress, and 9-cis epoxy carotenoid dioxygenase (NCED) is related to the indirect synthesis of ABA. However, NCED genes involved in multi-abiotic stress and ABA synthesis pathway in mulberry (Morus alba L.) are still unknown. Here, two NCED genes cloned from mulberry (MaNCED) and their function were preliminarily identified. Interestingly, MaNCED2 responded strongly to drought stress while MaNCED1 responded strongly to pathogen stress. Then, two MaNCED proteins were successfully obtained by prokaryotic expression, and the degradation products of MaNCED1 and MaNCED2 were analyzed using UPLC-MS. The results show that recombinant MaNCED1 and MaNCED2 both cleave 9-cis-violaxanthin to form C₁₅ xanthoxin, involved in the formation of the precursor of ABA.

Evolutionary Origin of the Carotenoid Cleavage Oxygenase Family in Plants and Expression of Pepper Genes in Response to Abiotic Stresses

Plant carotenoid cleavage oxygenase (CCO) is an enzyme that catalyzes the synthesis of carotenoids and participates in many important physiological functions. The plant CCOs exist in two forms, namely carotenoid cleavage dioxygenase (CCD) and nine-cis epoxide carotenoid dioxygenase (NCED). Although studies have shown that this gene family has been identified in many species, such as Arabidopsis, grape, and tomato, the evolutionary origin of the CCO family and the expression pattern of pepper genes in response to H₂O₂ and other abiotic stresses are still unclear. In this study, we used the bioinformatics method to identify and analyze the members of the CCO gene family from pepper and other 13 plants from lower to higher plant species based on the whole genome sequence. A total of 158 CCO genes were identified in different plant species and further divided into two groups (e.g., groups I and II). The former was subdivided into CCD7 and CCD8 and have independent evolutionary origins, respectively, while the latter was subdivided into CCD1, CCD4, CCD-like, and NCED, which may have come from a common ancestor. In addition, the results of RNA-seq showed that the expression patterns of pepper CaCCO genes were different in the tissues tested, and only few genes were expressed at high levels such as CaCCD1a, CaCCD4a, CaNCED3, and CaCCD1b. For hydrogen peroxide (H₂O₂) and other abiotic stresses, such as plant hormones, heat, cold, drought, and NaCl treatments, induction of about half of the CaCCO genes was observed. Moreover, the expression patterns of CaCCOs were further investigated under heat, cold, drought, and NaCl treatments using quantitative real-time PCR (qRT-PCR), and most members were responsive to these stresses, especially some CaCCOs with significant expression changes were identified, such as CaCCD4c, CaCCD-like1, CaCCD8, and CaCCD1b, suggesting the important roles of CaCCOs in abiotic stress responses. All these results will provide a valuable analytical basis for understanding the evolution and functions of the CCO family in plants.

A Novel WRKY Transcription Factor from Ipomoea trifida, ItfWRKY70, Confers Drought Tolerance in Sweet Potato

WRKY transcription factors are one of the important families in plants, and have important roles in plant growth, abiotic stress responses, and defense regulation. In this study, we isolated a WRKY gene, ItfWRKY70, from the wild relative of sweet potato Ipomoea trifida (H.B.K.) G. Don. This gene was highly expressed in leaf tissue and strongly induced by 20% PEG6000 and 100 μM abscisic acid (ABA). Subcellar localization analyses indicated that ItfWRKY70 was localized in the nucleus. Overexpression of ItfWRKY70 significantly increased drought tolerance in transgenic sweet potato plants. The content of ABA and proline, and the activity of SOD and POD were significantly increased, whereas the content of malondialdehyde (MDA) and H2O2 were decreased in transgenic plants under drought stress. Overexpression of ItfWRKY70 up-regulated the genes involved in ABA biosynthesis, stress-response, ROS-scavenging system, and stomatal aperture in transgenic plants under drought stress. Taken together, these results demonstrated that ItfWRKY70 plays a positive role in drought tolerance by accumulating the content of ABA, regulating stomatal aperture and activating the ROS scavenging system in sweet potato.

The moso bamboo WRKY transcription factor, PheWRKY86, regulates drought tolerance in transgenic plants

PheWRKY86 is a member of the WRKY transcription factor family in moso bamboo (Phyllostachys edulis). Expression of PheWRKY86 is strongly induced by drought and abscisic acid (ABA) treatments. The PheWRKY86 protein localizes to the cell nucleus and is specifically able to bind to W-box elements. 35S:PheWRKY86 transgenic Arabidopsis and rice showed significantly improved tolerance to drought stress. 35S:PheWRKY86 transgenic plants exhibited better water retention and lower relative electrolyte leakage (REL) and malondialdehyde (MDA) compared to wild type plants. Moreover, 35S:PheWRKY86 transgenic lines showed higher sensitivity to ABA stress. The 35S:PheWRKY86 transgenic plants exhibited higher ABA levels relative to wild type, while also exhibiting a lower germination rate, root length and fresh weight compared to wild type. Further analysis showed that expression of some ABA-responsive genes was changed in the 35S:PheWRKY86 transgenic lines under drought conditions. Transient expression and yeast one-hybrid assays demonstrated that PheWRKY86 could bind to the W-box element in the promoter region of NCED1. Taken together, these results demonstrate that PheWRKY86 plays a positive role in drought tolerance by regulating NCED1 expression.

Cold Stress in Citrus: A Molecular, Physiological and Biochemical Perspective

Due to climate change, we are forced to face new abiotic stress challenges like cold and heat waves that currently result from global warming. Losses due to frost and low temperatures force us to better understand the physiological, hormonal, and molecular mechanisms of response to such stress to face losses, especially in tropical and subtropical crops like citrus fruit, which are well adapted to certain weather conditions. Many of the responses to cold stress that are found are also conserved in citrus. Hence, this review also intends to show the latest work on citrus. In addition to basic research, there is a great need to employ and cultivate new citrus rootstocks to better adapt to environmental conditions.

The Combination of Abscisic Acid (ABA) and Water Stress Regulates the Epicuticular Wax Metabolism and Cuticle Properties of Detached Citrus Fruit

The phytohormone abscisic acid (ABA) is a major regulator of fruit response to water stress, and may influence cuticle properties and wax layer composition during fruit ripening. This study investigates the effects of ABA on epicuticular wax metabolism regulation in a citrus fruit cultivar with low ABA levels, called Pinalate (Citrus sinensis L. Osbeck), and how this relationship is influenced by water stress after detachment. Harvested ABA-treated fruit were exposed to water stress by storing them at low (30-35%) relative humidity. The total epicuticular wax load rose after fruit detachment, which ABA application decreased earlier and more markedly during fruit-dehydrating storage. ABA treatment changed the abundance of the separated wax fractions and the contents of most individual components, which reveals dependence on the exposure to postharvest water stress and different trends depending on storage duration. A correlation analysis supported these responses, which mostly fitted the expression patterns of the key genes involved in wax biosynthesis and transport. A cluster analysis indicated that storage duration is an important factor for the exogenous ABA influence and the postharvest environment on epicuticular wax composition, cuticle properties and fruit physiology. Dynamic ABA-mediated reconfiguration of wax metabolism is influenced by fruit exposure to water stress conditions.

MaWRKY80 positively regulates plant drought stress resistance through modulation of abscisic acid and redox metabolism

WRKY transcription factors play key roles in plant biotic and abiotic stress responses, but the function of some MaWRKYs remains elusive. Here, we characterized the positive role of MaWRKY80 in drought stress resistance and the underlying mechanism. MaWRKY80 was significantly upregulated under drought stress and confirmed as a transcription factor that could bind to the W-box. Overexpression of MaWRKY80 in Arabidopsis showed better phenotypic morphology, higher survival rate, less water loss rate, and lower malondialdehyde level than wild type (WT) under drought stress. Consistently, MaWRKY80 transgenic Arabidopsis leaves displayed significantly lower reactive oxygen species (ROS) than WT under drought stress. Moreover, MaWRKY80 mediated the stomata movement and leaf water retention capacity through modulation of the transcript of 9-cis-epoxycarotenoid dioxygenases (NCEDs) and abscisic acid (ABA) biosynthesis in Arabidopsis. Notably, chromatin immunoprecipitation quantitative real-time PCR (ChIP-PCR) and electrophoretic mobility shift assay (EMSA) provided evidences supporting the direct and specific interaction between MaWRKY80 and both the W-box in AtNCEDs promoter in Arabidopsis and the W-box in MaNCEDs promoter in banana. Taken together, MaWRKY80 serves as a positive regulator of drought stress resistance through modulating ABA level by regulating NCEDs expression and ROS accumulation by regulating antioxidant system. This study provides a novel insight into MaWRKY80 in coordinating ABA synthesis and ROS elimination in response to drought stress.

The unknown soldier in citrus plants: polyamines-based defensive mechanisms against biotic and abiotic stresses and their relationship with other stress-associated metabolites

Citrus plants are challenged by a broad diversity of abiotic and biotic stresses, which definitely alter their growth, development, and productivity. In order to survive the various stressful conditions, citrus plants relay on multi-layered adaptive strategies, among which is the accumulation of stress-associated metabolites that play vital and complex roles in citrus defensive responses. These metabolites included amino acids, organic acids, fatty acids, phytohormones, polyamines (PAs), and other secondary metabolites. However, the contribution of PAs pathways in citrus defense responses is poorly understood. In this review article, we will discuss the recent metabolic, genetic, and molecular evidence illustrating the potential roles of PAs in citrus defensive responses against biotic and abiotic stressors. We believe that PAs-based defensive role, against biotic and abiotic stress in citrus, is involving the interaction with other stress-associated metabolites, particularly phytohormones. The knowledge gained so far about PAs-based defensive responses in citrus underpins our need for further genetic manipulation of PAs biosynthetic genes to produce transgenic citrus plants with modulated PAs content that may enhance the tolerance of citrus plants against stressful conditions. In addition, it provides valuable information for the potential use of PAs or their synthetic analogs and their emergence as a promising approach to practical applications in citriculture to enhance stress tolerance in citrus plants.

The chaperone MeHSP90 recruits MeWRKY20 and MeCatalase1 to regulate drought stress resistance in cassava

The 90 kDa heat shock protein (HSP90) is widely involved in various developmental processes and stress responses in plants. However, the molecular chaperone HSP90-constructed protein complex and its function in cassava remain elusive. In this study, we report that HSP90 is essential for drought stress resistance in cassava by regulating abscisic acid (ABA) and hydrogen peroxide (H₂ O₂ ) using two specific protein inhibitors of HSP90 (geldanamycin (GDA) and radicicol (RAD)). Among 10 MeHSP90s, the transcript of MeHSP90.9 is largely induced during drought stress. Further investigation identifies MeWRKY20 and MeCatalase1 as MeHSP90.9-interacting proteins. MeHSP90.9-, MeWRKY20-, or MeCatalase1-silenced plants through virus-induced gene silencing display drought sensitivity in cassava, indicating that they are important to drought stress response. MeHSP90.9 can promote the direct transcriptional activation of MeWRKY20 on the W-box element of MeNCED5 promoter, encoding a key enzyme in ABA biosynthesis. Moreover, MeHSP90.9 positively regulates the activity of MeCatalase1, and MeHSP90.9-silenced cassava leaves accumulate more H₂ O₂ under drought stress. Taken together, we demonstrate that the MeHSP90.9 chaperone complex is a regulator of drought stress resistance in cassava.

The β-amylase PbrBAM3 from pear (Pyrus betulaefolia) regulates soluble sugar accumulation and ROS homeostasis in response to cold stress

β-Amylase (BAM) is involved in sugar metabolism, but the role of BAM genes in cold tolerance remains poorly understood. Here, we report the identification and functional characterization of the chloroplast-localized BAM-encoding gene PbrBAM3 isolated from Pyrus betulaefolia. The transcript levels of PbrBAM3 were up-regulated under cold, dehydration and ABA, but repressed by maltose. Overexpression of PbrBAM3 in tobacco (Nicotiana tabacum) and pear (P. ussuriensis) conferred increased BAM activity, promoted starch degradation after chilling treatments and enhanced tolerance to cold. Under the chilling stress, the transgenic tobacco and P. ussuriensis exhibited lessened reactive oxygen species (ROS) generation, higher levels of antioxidant enzymes activity, and greater accumulation of soluble sugars (specially maltose) than the corresponding wild type plants. Taken together, these results demonstrate that PbrBAM3 plays an important role in cold tolerance, at least in part, by raising the levels of soluble sugars capable of acting as osmolytes or antioxidants.

OsNCED5, a 9-cis-epoxycarotenoid dioxygenase gene, regulates salt and water stress tolerance and leaf senescence in rice

9-cis-epoxycarotenoid dioxygenase (NCED) is a rate-limiting enzyme for abscisic acid (ABA) biosynthesis. However, the molecular mechanisms of NCED5 that modulate plant development and abiotic stress tolerance are still unclear, particular in rice. Here, we demonstrate that a rice NCED gene, OsNCED5, was expressed in all tissues we tested, and was induced by exposure to salt stress, water stress, and darkness. Mutational analysis showed that nced5 mutants reduced ABA level and decreased tolerance to salt and water stress and delayed leaf senescence. However, OsNCED5 overexpression increased ABA level, enhanced tolerance to the stresses, and accelerated leaf senescence. Transcript analysis showed that OsNCED5 regulated ABA-dependent abiotic stress and senescence-related gene expression. Additionally, ectopic expression of OsNCED5 tested in Arabidopsis thaliana altered plant size and leaf morphology and delayed seed germination and flowering time. Thus, OsNCED5 may regulate plant development and stress resistance through control of ABA biosynthesis. These findings contribute to our understanding of the molecular mechanisms by which NCED regulates plant development and responses to abiotic stress in different crop species.

A WRKY transcription factor PbrWRKY53 from Pyrus betulaefolia is involved in drought tolerance and AsA accumulation

WRKY comprises a large family of transcription factors in plants, but most WRKY members are still poorly understood. In this study, we report the identification and functional characterization of PbrWRKY53 isolated from Pyrus betulaefolia. PbrWRKY53 was greatly up-regulated by drought and abscisic acid, but slightly induced by salt and cold. Subcellar localization analyses showed that PbrWRKY53 was located in the nucleus. Ectopic expression of PbrWRKY53 in tobacco and Pyrus ussuriensis conferred enhanced tolerance to drought stress. The transgenic plants exhibited better water status, less reactive oxygen species generation and higher levels of antioxidant enzyme activities and metabolites than the wild type. In addition, overexpression of PbrWRKY53 in transgenic tobacco resulted in enhanced expression level of PbrNCED1, and led to the increase in larger amount of vitamin C accumulation in comparison to WT. Knock-down of PbrWRKY53 in P. ussuriensis down-regulated PbrNCED1 abundance, accompanied by compromised drought tolerance. Yeast one-hybrid assay, EMSA and transient expression analysis demonstrated that PbrWRKY53 could bind to the W-box element in the promoter region of PbrNCED1. Taken together, these results demonstrated that PbrWRKY53 plays a positive role in drought tolerance, which might be, at least in part, promoting production of vitamin C via regulating PbrNCED1 expression.

Phytohormones as targets for improving plant productivity and stress tolerance

In this review, we summarize the results of experiments that lead to altered levels of phytohormones in transgenic plants to improve plant productivity. The available data indicate that manipulating the level of phytohormones might also be a promising way to enhance the environmental stress tolerance of crop plants. In the regulation of the level of phytohormones, both biosynthesis and their catabolism pathways can be targeted for engineering purposes. Moreover, the signaling pathways of phytohormones should explored in this respect. In genetic modifications, conditional promoters must be developed to avoid undesired effects on growth. In order to find a practical application, the effects of genetic modifications should be further verified under field conditions and over a longer time scale.

Effect of the Winter Wheat Cheyenne 5A Substituted Chromosome on Dynamics of Abscisic Acid and Cytokinins in Freezing-Sensitive Chinese Spring Genetic Background

The effect of short- and long-term cold treatment on the abscisic acid (ABA) and cytokinin (CK) metabolism, and their main biosynthesis- and signaling-related genes were investigated in freezing-sensitive and freezing-tolerant wheat genotypes. Varieties Cheyenne and Chinese Spring substituted with the 5A Cheyenne chromosome, which represented freezing-tolerant genotypes, were compared with the freezing-sensitive Chinese Spring. Hormone levels and gene expression data indicated that the short- and long-term cold treatments are associated with specific regulation of the accumulation of cold-protective proteins and phytohormone levels, as well as the expression profiles of the hormone-related genes. The significant differences were observed between the genotypes, and between their leaf and crown tissues, too. The level of dehydrins, including WCS120 protein, and expression of WCS120 gene were considerably higher in the freezing-tolerant genotypes after 21 days of cold treatment. Expression of Cor14b and CBF14, cold-responsive regulator genes, was increased by cold treatment in all genotypes, to higher extent in freezing-tolerant genotypes. Cluster analysis revealed that the tolerant genotypes had a similar response to cold treatment, regarding expression of the ABA and CK metabolic genes, as well as hormone levels in leaves. As far as hormone levels in crowns are concerned, however, the strongly freezing-tolerant Cheyenne variety clustered separately from the Chinese Spring and the substitution line, which were more similar to each other after both 1 and 21 days of cold treatment than to Cheyenne. Based on these results we concluded that the 5A chromosome of wheat might have both a direct and an indirect impact on the phytohormone-dependent cold-induced freezing tolerance. Based on the gene expression data, novel genetic markers could be developed, which may be used to determine the freezing tolerance level in a wide range of wheat varieties.

Molecular cloning and characterization of PtrZPT2-1, a ZPT2 family gene encoding a Cys2/His2-type zinc finger protein from trifoliate orange (Poncirus trifoliata (L.) Raf.) that enhances plant tolerance to multiple abiotic stresses

In plants, most Cys2/His2 (C2H2) zinc finger proteins with two zinc finger domains (ZPT2) are involved in abiotic stress responses. In this study, a ZPT2 family gene PtrZPT2-1 was cloned from trifoliate orange (Poncirus trifoliata (L.) Raf.). PtrZPT2-1 is composed of 245 amino acids, has a putative molecular weight of 25.99kDa and an isoelectric point of 8.41. PtrZPT2-1 contained two C2H2 zinc finger domains, one nuclear localization signal (B-box), one transcription repression domain (DLN-box), and one protein-protein interaction domain (L-box). PtrZPT2-1 was localized to the nucleus. The PtrZPT2-1 expression was strongly induced by cold, drought, salt and ABA stresses. Overexpression of PtrZPT2-1 increased the survival rates, and the ABA, soluble sugar and proline levels but decreased the ion leakage, the malondialdehyde (MDA) content and reduced the H2O2 accumulation in the transgenic tobacco after cold, drought or salt treatments. Furthermore, the expression levels of 15 abiotic stress-related genes were significantly increased in the transgenic tobacco overexpressing PtrZPT2-1 after cold, drought or salt stress treatments. Our results indicated that overexpression of PtrZPT2-1 in the transgenic tobacco could improve the cold, drought and salt resistance of the plants by increasing the levels of osmotic regulatory solutes and decreasing the accumulation of H2O2.

Effects of drought stress on global gene expression profile in leaf and root samples of Dongxiang wild rice (Oryza rufipogon)

Drought is a serious constraint to rice production throughout the world, and although Dongxiang wild rice (Oryza rufipogon, DXWR) possesses a high degree of drought resistance, the underlying mechanisms of this trait remains unclear. In the present study, cDNA libraries were constructed from the leaf and root tissues of drought-stressed and untreated DXWR seedlings, and transcriptome sequencing was performed with the goal of elucidating the molecular mechanisms involved in drought-stress response. The results indicated that 11231 transcripts were differentially expressed in the leaves (4040 up-regulated and 7191 down-regulated) and 7025 transcripts were differentially expressed in the roots (3097 up-regulated and 3928 down-regulated). Among these differentially expressed genes (DEGs), the detection of many transcriptional factors and functional genes demonstrated that multiple regulatory pathways were involved in drought resistance. Meanwhile, the DEGs were also annotated with gene ontology (GO) terms and key pathways via functional classification and Kyoto Encyclopedia of Gene and Genomes (KEGG) pathway mapping, respectively. A set of the most interesting candidate genes was then identified by combining the DEGs with previously identified drought-resistant quantitative trait loci (QTL). The present work provides abundant genomic information for functional dissection of the drought resistance of DXWR, and findings will further help the current understanding of the biological regulatory mechanisms of drought resistance in plants and facilitate the breeding of new drought-resistant rice cultivars.

The improvement of salt tolerance in transgenic tobacco by overexpression of wheat F-box gene TaFBA1

F-box protein is a major subunit of the Skp1-Cullin-F-box (SCF) complex. We previously isolated an F-box gene from wheat, TaFBA1, and here we show that overexpression of TaFBA1 in transgenic plants under salt stress increases germination rate, root elongation, and biomass accumulation compared with WT plants. Improvements in the photosynthetic rate and its corresponding parameters were also found in the transgenic plants. These results suggest that overexpression of TaFBA1 improves salt stress tolerance in transgenic tobacco. Further, the transgenic plants displayed less membrane damage, higher antioxidant enzyme activity, and less accumulation of ROS under salt stress. The transgenic plants also had lower Na+ content and higher K+ content than WT plants in leaves and roots. The activity of H+-ATPase on the plasma membrane in the transgenic plants was higher than in WT plants, and was accompanied by a net Na+ efflux. In the tonoplast, the activity levels of V-ATPase and PPase were also higher in the transgenic plants, thus helping to maximize intracellular Na+ compartmentalization. The expression of some stress-related genes was upregulated by salt stress. This suggests that the enhancement of plant salt stress tolerance may be associated with an improvement in antioxidative competition and Na+/K+ ion regionalization.

Combined analysis of mRNA and miRNA identifies dehydration and salinity responsive key molecular players in citrus roots

Citrus is one of the most economically important fruit crops around world. Drought and salinity stresses adversely affected its productivity and fruit quality. However, the genetic regulatory networks and signaling pathways involved in drought and salinity remain to be elucidated. With RNA-seq and sRNA-seq, an integrative analysis of miRNA and mRNA expression profiling and their regulatory networks were conducted using citrus roots subjected to dehydration and salt treatment. Differentially expressed (DE) mRNA and miRNA profiles were obtained according to fold change analysis and the relationships between miRNAs and target mRNAs were found to be coherent and incoherent in the regulatory networks. GO enrichment analysis revealed that some crucial biological processes related to signal transduction (e.g. ‘MAPK cascade’), hormone-mediated signaling pathways (e.g. abscisic acid- activated signaling pathway’), reactive oxygen species (ROS) metabolic process (e.g. ‘hydrogen peroxide catabolic process’) and transcription factors (e.g., ‘MYB, ZFP and bZIP’) were involved in dehydration and/or salt treatment. The molecular players in response to dehydration and salt treatment were partially overlapping. Quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) analysis further confirmed the results from RNA-seq and sRNA-seq analysis. This study provides new insights into the molecular mechanisms how citrus roots respond to dehydration and salt treatment.

Comparative transcriptome profiling of chilling stress responsiveness in grafted watermelon seedlings

Rootstock grafting may improve the resistance of watermelon plants to low temperatures. However, information regarding the molecular responses of rootstock grafted plants to chilling stress is limited. To elucidate the molecular mechanisms of chilling tolerance in grafted plants, the transcriptomic responses of grafted watermelon under chilling stress were analyzed using RNA-seq analysis. Sequencing data were used for digital gene expression (DGE) analysis to characterize the transcriptomic responses in grafted watermelon seedlings. A total of 702 differentially-expressed genes (DEGs) were found in rootstock grafted (RG) watermelon relative to self-grafted (SG) watermelon; among these genes, 522 genes were up-regulated and 180 were down-regulated. Additionally, 164 and 953 genes were found to specifically expressed in RG and SG seedlings under chilling stress, respectively. Functional annotations revealed that up-regulated DEGs are involved in protein processing, plant-pathogen interaction and the spliceosome, whereas down-regulated DEGs are associated with photosynthesis. Moreover, 13 DEGs were randomly selected for quantitative real time PCR (qRT-PCR) analysis. The expression profiles of these 13 DEGs were consistent with those detected by the DGE analysis, supporting the reliability of the DGE data. This work provides additional insight into the molecular basis of grafted watermelon responses to chilling stress.

Abscisic acid metabolic genes of wheat (Triticum aestivum L.): identification and insights into their functionality in seed dormancy and dehydration tolerance

The three homeologues of wheat NCED2 were identified; the wheat NCED2A and CYP707A1B affect seed ABA level and dormancy but not leaf ABA level and transpirational water loss in Arabidopsis. Biosynthesis and catabolism of abscisic acid (ABA) in plants are primarily regulated by 9-cis-epoxycarotenoid dioxygenases (NCEDs) and ABA 8'-hydroxylase (ABA8'OH), respectively. The present study identified the complete coding sequences of a second NCED gene, designated as TaNCED2, and its homeologues (TaNCED2A, TaNCED2B and TaNCED2D) in hexaploid wheat, and characterized its functionality in seed dormancy and leaf dehydration tolerance using the TaNCED2A homeologue. The study also investigated the role of the B genome copy of the cytochrome P450 monooxygenase 707A1 (CYP707A1) gene of hexaploid wheat (TaCYP707A1B), which encodes ABA8'OH, in regulating the two traits as this has not been studied before. Ectopic expression of TaNCED2A and TaCYP707A1B in Arabidopsis resulted in altered seed ABA level and dormancy with no effect on leaf ABA content and transpirational water loss. To gain insights into the physiological roles of TaNCED2 and TaCYP707A1 in wheat, the study examined their spatiotemporal expression patterns and determined the genomic contributions of transcripts to their total expression.

Overexpression of Rosa rugosa anthocyanidin reductase enhances tobacco tolerance to abiotic stress through increased ROS scavenging and modulation of ABA signaling

Anthocyanidin reductase (ANR) is a key enzyme involved in the biosynthesis of proanthocyanidins (PAs) and plays a role in the plant stress response. However, the mechanism by which ANR confers stress tolerance in plants is not understood. Here, we report the isolation of RrANR, the homologous gene from rose, and NtABF, an ABA-response related transcription factor gene from tobacco. These genes were characterized regarding their functions in stress responses through the use of transgenic, transcriptomic and physiological analyses. Over-expression of RrANR in tobacco resulted in an increased accumulation of both PAs and abscisic acid (ABA), and also enhanced stress tolerance. Transcriptomic analysis of these transgenic tobacco lines indicated that RrANR overexpression induced global transcriptomic changes, including these involved in oxidation/reduction, hormone response and secondary metabolism. Genes related to ABA biosynthesis and reactive oxygen species (ROS)-scavenging were up-regulated in RrANR transgenic lines, and these effects were phenocopied by the direct treatment of tobacco plants with PAs and ABA. Transcriptomic data from each of these treatments identified the upregulation of a putative NtABF. Furthermore, the up-regulation of NtABF in RrANR transformants or in PAs- and ABA-treated tobacco plants was associated with enhanced stress tolerance. Overexpression of NtABF in transgenic tobacco mimicked the effects of RrANR-transgenic plants with regard to the up-regulation of ROS-scavenging genes and an increase in oxidative tolerance. Taken together, our findings indicate that overexpression of RrANR results in an increase in plant tolerance to oxidative stress via increased scavenging of ROS and modulation of the ABA signaling pathway.

Overexpression of a bHLH1 Transcription Factor of Pyrus ussuriensis Confers Enhanced Cold Tolerance and Increases Expression of Stress-Responsive Genes

The basic helix-loop-helix (bHLH) transcription factors are involved in arrays of physiological and biochemical processes. However, knowledge concerning the functions of bHLHs in cold tolerance remains poorly understood. In this study, a PubHLH1 gene isolated from Pyrus ussuriensis was characterized for its function in cold tolerance. PubHLH1 was upregulated by cold, salt, and dehydration, with the greatest induction under cold conditions. PubHLH1 had the transactivational activity and localized in the nucleus. Ectopic expression of PubHLH1 in transgenic tobacco conferred enhanced tolerance to cold stress. The transgenic lines had higher survival rates, higher chlorophyll, higher proline contents, lower electrolyte leakages and MDA when compared with wild type (WT). In addition, transcript levels of eight genes associated with ROS scavenging, regulation, and stress defense were higher in the transgenic plants relative to the WT under the chilling stress. Taken together, these results demonstrated that PubHLH1 played a key role in cold tolerance and, at least in part, contributed to activation of stress-responsive genes.

MhNCED3 in Malus hupehensis Rehd. induces NO generation under osmotic stress by regulating ABA accumulation

Abscisic acid (ABA) biosynthesis has been widely characterized in plants, whereas the effects of ABA biosynthesis on nitric oxide (NO) generation in osmotic stress are less well understood. In this study, Malus hupehensis Rehd. 9-cis-epoxycarotenoid dioxygenase gene (MhNCED3) which is the key gene in ABA biosynthesis was transformed into wild type (WT) and 129B08/nced3 mutant (AtNCED3 deficient), respectively, and two transgenic Arabidopsis lines were obtained. The transgenic Arabidopsis lines displayed higher endogenous ABA content, NO generation rate, AtNIA1 transcript level and nitrate reductase (NR) activity than WT and 129B08/nced3 mutant. Ectopic expression of MhNCED3 reduced the electrolyte leakage and relieved Arabidopsis damage caused by 20% PEG on the growth and development. The ABA content, NO generation rate, AtNIA1 expression and NR activity increased after 20% PEG treatment, importantly, their increases amplitude relative to that in control were higher in two transgenic lines. Additionally, during the treatment for the four genotype Arabidopsis, the time of ABA contents reaching the highest peak was earlier than the time of NO generation, AtNIA1 expression and NR activity reaching their highest peak. These results show that NCED gene indirectly induced endogenous NO generation in osmotic-stressed Arabidopsis partially contributing to the up-regulation of AtNIA1 expression and NR activity.

Overexpression of SpWRKY1 promotes resistance to Phytophthora nicotianae and tolerance to salt and drought stress in transgenic tobacco

WRKY transcription factors are key regulatory components of plant responses to biotic and abiotic stresses. SpWRKY1, a pathogen-induced WRKY gene, was isolated from tomato (Solanum pimpinellifolium L3708) using in silico cloning and reverse transcriptase-polymerase chain reaction (RT-PCR) methods. SpWRKY1 expression was significantly induced following oomycete pathogen infection and treatment with salt, drought, salicylic acid (SA), methyl jasmonate (MeJA) and abscisic acid (ABA). Overexpression of SpWRKY1 in tobacco conferred greater resistance to Phytophthora nicotianae infection, as evidenced by lower malondialdehyde (MDA) content; relative electrolyte leakage (REL); higher chlorophyll content; and higher peroxidase (POD, EC 1.11.1.7), superoxide dismutase (SOD, EC 1.15.1.1) and phenylalanine ammonia-lyase (PAL, EC 4.3.1.24) activities. This resistance was also coupled with enhanced expression of SA- and JA-associated genes (NtPR1, NtPR2, NtPR4, NtPR5 and NtPDF1.2), as well as of various defense-related genes (NtPOD, NtSOD and NtPAL). In addition, transgenic tobacco plants also displayed an enhanced tolerance to salt and drought stresses, mainly demonstrated by the transgenic lines exhibiting lower accumulation of MDA content and higher POD (EC 1.11.1.7), SOD (EC 1.15.1.1) activities, chlorophyll content, photosynthetic rate and stomatal conductance, accompanied by enhanced expression of defense-related genes (NtPOD, NtSOD, NtLEA5, NtP5CS and NtNCED1) under salt and drought stresses. Overall, these findings suggest that SpWRKY1 acts as a positive regulator involved in tobacco defense responses to biotic and abiotic stresses.

MicroRNA and mRNA expression profiling analysis revealed the regulation of plant height in Gossypium hirsutum

BACKGROUND

Dwarf cottons are more resistant to damage from wind and rain and associated with stable, increased yields, and also desirable source for breeding the machine harvest varieties. In an effort to uncover the transcripts and miRNA networks involved in plant height, the transcriptome and small RNA sequencing were performed based on dwarf mutant Ari1327 (A1), tall-culm mutant Ari3697 (A3) and wild type Ari971 (A9) in Gossypium hirsutum.

METHODS

The stem apexes of wild-type upland cotton (Ari971) and its dwarf mutant (Ari1327) and tall-culm mutant (Ari3697) at the fifth true leaf stage were extracted for RNA, respectively. Transcriptome and small RNA libraries were constructed and subjected to next generation sequencing.

RESULTS

The transcriptome sequencing analysis showed that the enriched pathways of top 3 differentially expressed genes (DEGs) were categorized as carotenoid biosynthesis, plant-pathogen interaction and plant hormone signal transduction in both A1-A9 and A3-A9. The ABA and IAA related factors were differentially expressed in the mutants. Importantly, we found the lower expressed SAUR and elevated expressed GH3, and ABA related genes such as NCED and PP2C maybe relate to reduced growth of the plant height in Ari1327 which was consistent with the higher auxin and ABA content in this mutant. Furthermore, miRNA160 targeted to the auxin response factor (ARF) and miRNA166 (gma-miR166u and gma-miR166h-3p) targeted to ABA responsive element binding factor were related to the mutation in cotton. We have noticed that the cell growth related factors (smg7 targeted by gra-miR482 and 6 novel miRNAs and pectate-lyases targeted by osa-miR159f), the redox reactions related factors (Cytochrome P450 targeted by miR172) and MYB genes targeted by miR828, miR858 and miR159 were also involved in plant height of the cotton mutants. A total of 226 conserved miRNAs representing 32 known miRNA families were obtained, and 38 novel miRNAs corresponding to 23 unique RNA sequences were identified. Total 531 targets for 211 conserved miRNAs were obtained. Using PAREsnip, 27 and 29 miRNA/target conserved interactions were validated in A1-A9 and A3-A9, respectively. Furthermore, miRNA160, miRNA858 and miRNA172 were validated to be up-regulated in A1-A9 but down-regulated in A3-A9, whereas miRNA159 showed the opposite regulation.

CONCLUSIONS

This comprehensive interaction of the transcriptome and miRNA at tall-culm and dwarf mutant led to the discovery of regulatory mechanisms in plant height. It also provides the basis for in depth analyses of dwarf mutant genes for further breeding of dwarf cotton.

PtrABF of Poncirus trifoliata functions in dehydration tolerance by reducing stomatal density and maintaining reactive oxygen species homeostasis

Abscisic acid-responsive element (ABRE)-binding factors (ABFs) play important roles in abiotic stress responses; however, the underlying mechanisms are poorly understood. In this study, it is reported that overexpression of Poncirus trifoliata PtrABF significantly enhanced dehydration tolerance. The transgenic lines displayed smaller stomatal apertures, reduced stomatal density/index, and lower expression levels of genes associated with stomatal development. PtrABF was found to interact with PtrICE1, a homologue of ICE1 (Inducer of CBF Expression 1) that has been shown to be critical for stomatal development. Microarray analysis revealed that a total of 70 genes were differentially expressed in the transgenic line, 42 induced and 28 repressed. At least two units of ABREs and coupling elements were present in the promoters of most of the induced genes, among which peroxidase and arginine decarboxylase were verified as bona fide targets of PtrABF. Transgenic plants exhibited higher antioxidant enzyme activities and free polyamine levels, but lower levels of reactive oxygen species (ROS) and malondialdehyde. Polyamines were revealed to be associated with ROS scavenging in the transgenic plants due to a modulation of antioxidant enzymes triggered by signalling mediated by H2O2 derived from polyamine oxidase (PAO)-mediated catabolism. Taken together, the results indicate that PtrABF functions positively in dehydration tolerance by limiting water loss through its influence on stomatal movement or formation and maintaining ROS homeostasis via modulation of antioxidant enzymes and polyamines through transcriptional regulation of relevant target genes.

Cloning and functional validation of molybdenum cofactor sulfurase gene from Ammopiptanthus nanus

The molybdenum cofactor sulfurase gene ( AnMCSU ) was cloned from xerophytic desert plant Ammopiptanthus nanus and validated for its function of tolerance toward abiotic stresses by heterologous expression in Arabidopsis thaliana. Molybdenum cofactor sulfurase participates in catalyzing biosynthesis of abscisic acid, which plays a crucial role in the response of plants to abiotic stresses. In this study, we cloned molybdenum cofactor sulfurase gene (AnMCSU) from a super-xerophytic desert plant, Ammopiptanthus nanus, by using rapid amplification of cDNA ends method. This gene has a total length of 2544 bp, with a 5'- and a 3'-untranslated region of 167 and 88 bp, and an open reading frame of 2289 bp, which encodes an 84.85 kDa protein of 762 amino acids. The putative amino acid sequence shares high homology and conserved amino acid residues crucial for the function of molybdenum cofactor sulfurases with other leguminous species. The encoded protein of the AnMCSU gene was located in the cytoplasm by transient expression in Nicotiana benthamiana. The result of real-time quantitative PCR showed that the expression of the AnMCSU gene was induced by heat, dehydration, high salt stresses, and ABA induction, and inhibited by cold stress. The heterologous expression of the AnMCSU gene significantly enhanced the tolerance of Arabidopsis thaliana to high salt, cold, osmotic stresses, and abscisic acid induction. All these results suggest that the AnMCSU gene might play a crucial role in the adaptation of A. nanus to abiotic stress and has potential to be applied to transgenic improvement of commercial crops.

DroughtDB: an expert-curated compilation of plant drought stress genes and their homologs in nine species

Plants are sessile and therefore exposed to a number of biotic and abiotic stresses. Drought is the major abiotic stress restricting plant growth worldwide. A number of genes involved in drought stress response have already been characterized, mainly in the model species Arabidopsis thaliana and Oryza sativa. However, with the aim to produce drought tolerant crop varieties, it is of importance to identify the respective orthologs for each species. We have developed DroughtDB, a manually curated compilation of molecularly characterized genes that are involved in drought stress response. DroughtDB includes information about the originally identified gene, its physiological and/or molecular function and mutant phenotypes and provides detailed information about computed orthologous genes in nine model and crop plant species including maize and barley. All identified orthologs are interlinked with the respective reference entry in MIPS/PGSB PlantsDB, which allows retrieval of additional information like genome context and sequence information. Thus, DroughtDB is a valuable resource and information tool for researchers working on drought stress and will facilitate the identification, analysis and characterization of genes involved in drought stress tolerance in agriculturally important crop plants.

Database URL:http://pgsb.helmholtz-muenchen.de/droughtdb/

MhNCED3, a gene encoding 9-cis-epoxycarotenoid dioxygenase in Malus hupehensis Rehd., enhances plant tolerance to Cl- stress by reducing Cl- accumulation

High Cl(-) concentrations in tissues can be toxic to crop plants and may lead to reduced growth rates and yields. 9-cis-epoxycarotenoid dioxygenase (NCED) is thought to be involved in the biosynthesis of abscisic acid (ABA), which is an important regulator of plant adaptive responses to stress. Here, the expression of MhNCED3 in Malus hupehensis Rehd. and the effects of MhNCED3 on plant tolerance to Cl(-) stress were explored. The results showed that MhNCED3 expression and ABA biosynthesis in M. hupehensis Rehd. were induced by Cl(-) stress. Ectopic expression of MhNCED3 in Arabidopsis complemented the phenotypic defects of the 129B08/nced3 mutant and enhanced WT tolerance to Cl(-) stress. The transgenic Arabidopsis showed improved growth and developmental status, increased ABA contents, and reduced transpiration rates and relative water content. Furthermore, ectopic expression of MhNCED3 decreased Cl(-) accumulation and oxidative damage, and up-regulated the expression levels of AtCLCc (chloride channel protein) and AtSLAH3 (slow anion channel 1 homolog 3) genes in Arabidopsis. These observations suggest that MhNCED3 has critical role in enhancing plant tolerance to Cl(-) stress by reducing Cl(-) accumulation.

Transcriptomic analysis of the primary roots of Alhagi sparsifolia in response to water stress

BACKGROUND

Alhagi sparsifolia is a typical desert phreatophyte and has evolved to withstand extreme dry, cold and hot weather. While A. sparsifolia represents an ideal model to study the molecular mechanism of plant adaption to abiotic stress, no research has been done in this aspect to date. Here we took advantage of Illumina platform to survey transcriptome in primary roots of A. sparsifolia under water stress conditions in aim to facilitate the exploration of its genetic basis for drought tolerance.

METHODOLOGY AND PRINCIPAL FINDINGS

We sequenced four primary roots samples individually collected at 0, 6, 24 and 30h from the A. sparsifolia seedlings in the course of 24h of water stress following 6h of rehydration. The resulting 38,763,230, 67,511,150, 49,259,804 and 54,744,906 clean reads were pooled and assembled into 33,255 unigenes with an average length of 1,057 bp. All-unigenes were subjected to functional annotation by searching against the public databases. Based on the established transcriptome database, we further evaluated the gene expression profiles in the four different primary roots samples, and identified numbers of differently expressed genes (DEGs) reflecting the early response to water stress (6h vs. 0h), the late response to water stress (24h vs. 0h) and the response to post water stress rehydration (30h vs. 24h). Moreover, the DEGs specifically regulated at 6, 24 and 30h were captured in order to depict the dynamic changes of gene expression during water stress and subsequent rehydration. Functional categorization of the DEGs indicated the activation of oxidoreductase system, and particularly emphasized the significance of the 'Glutathione metabolism pathway' in response to water stress.

CONCLUSIONS

This is the first description of the genetic makeup of A. sparsifolia, thus providing a substantial contribution to the sequence resources for this species. The identified DEGs offer a deep insight into the molecular mechanism of A. sparsifolia in response to water stress, and merit further investigation.

Comparative study of the protein profiles of Sunki mandarin and Rangpur lime plants in response to water deficit

BACKGROUND

Rootstocks play a major role in the tolerance of citrus plants to water deficit by controlling and adjusting the water supply to meet the transpiration demand of the shoots. Alterations in protein abundance in citrus roots are crucial for plant adaptation to water deficit. We performed two-dimensional electrophoresis (2-DE) separation followed by LC/MS/MS to assess the proteome responses of the roots of two citrus rootstocks, Rangpur lime (Citrus limonia Osbeck) and 'Sunki Maravilha' (Citrus sunki) mandarin, which show contrasting tolerances to water deficits at the physiological and molecular levels.

RESULTS

Changes in the abundance of 36 and 38 proteins in Rangpur lime and 'Sunki Maravilha' mandarin, respectively, were observed via LC/MS/MS in response to water deficit. Multivariate principal component analysis (PCA) of the data revealed major changes in the protein profile of 'Sunki Maravilha' in response to water deficit. Additionally, proteomics and systems biology analyses allowed for the general elucidation of the major mechanisms associated with the differential responses to water deficit of both varieties. The defense mechanisms of Rangpur lime included changes in the metabolism of carbohydrates and amino acids as well as in the activation of reactive oxygen species (ROS) detoxification and in the levels of proteins involved in water stress defense. In contrast, the adaptation of 'Sunki Maravilha' to stress was aided by the activation of DNA repair and processing proteins.

CONCLUSIONS

Our study reveals that the levels of a number of proteins involved in various cellular pathways are affected during water deficit in the roots of citrus plants. The results show that acclimatization to water deficit involves specific responses in Rangpur lime and 'Sunki Maravilha' mandarin. This study provides insights into the effects of drought on the abundance of proteins in the roots of two varieties of citrus rootstocks. In addition, this work allows for a better understanding of the molecular basis of the response to water deficit in citrus. Further analysis is needed to elucidate the behaviors of the key target proteins involved in this response.

The rose (Rosa hybrida) NAC transcription factor 3 gene, RhNAC3, involved in ABA signaling pathway both in rose and Arabidopsis

Plant transcription factors involved in stress responses are generally classified by their involvement in either the abscisic acid (ABA)-dependent or the ABA-independent regulatory pathways. A stress-associated NAC gene from rose (Rosa hybrida), RhNAC3, was previously found to increase dehydration tolerance in both rose and Arabidopsis. However, the regulatory mechanism involved in RhNAC3 action is still not fully understood. In this study, we isolated and analyzed the upstream regulatory sequence of RhNAC3 and found many stress-related cis-elements to be present in the promoter, with five ABA-responsive element (ABRE) motifs being of particular interest. Characterization of Arabidopsis thaliana plants transformed with the putative RhNAC3 promoter sequence fused to the β-glucuronidase (GUS) reporter gene revealed that RhNAC3 is expressed at high basal levels in leaf guard cells and in vascular tissues. Moreover, the ABRE motifs in the RhNAC3 promoter were observed to have a cumulative effect on the transcriptional activity of this gene both in the presence and absence of exogenous ABA. Overexpression of RhNAC3 in A. thaliana resulted in ABA hypersensitivity during seed germination and promoted leaf closure after ABA or drought treatments. Additionally, the expression of 11 ABA-responsive genes was induced to a greater degree by dehydration in the transgenic plants overexpressing RhNAC3 than control lines transformed with the vector alone. Further analysis revealed that all these genes contain NAC binding cis-elements in their promoter regions, and RhNAC3 was found to partially bind to these putative NAC recognition sites. We further found that of 219 A. thaliana genes previously shown by microarray analysis to be regulated by heterologous overexpression RhNAC3, 85 are responsive to ABA. In rose, the expression of genes downstream of the ABA-signaling pathways was also repressed in RhNAC3-silenced petals. Taken together, we propose that the rose RhNAC3 protein could mediate ABA signaling both in rose and in A. thaliana.

A stress responsive gene of Fortunella crassifolia FcSISP functions in salt stress resistance

Exploration of genes functioning in salt tolerance is crucial for generating transgenic plants with enhanced salt tolerance. In this study, we report the isolation and functional characterization of a stress-responsive gene FcSISP from Meiwa kumquat (Fortunella crassifolia). FcSISP encodes a putative protein of 47 amino acids, with a calculated molecular mass of 4.94 kDa and theoretical isoelectric point of 3.76, and was localized in the nucleus. Transcript levels of FcSISP were induced by dehydration, cold, salt and bacterium causing citrus canker, and hormones (salicylic acid and abscisic acid), with the greatest induction under salt treatment. Overexpression of FcSISP in tobacco (Nicotiana nudicaulis) conferred enhanced salt tolerance. The transgenic lines accumulated lower Na(+) contents, leading to reduced Na/K ratio, but accumulated more proline than the wild type (WT). Steady state mRNA levels of genes involved in Na(+) exchange (three SOS genes and three NHX genes) and proline synthesis (P5CS and P5CR) were higher in the transgenic lines in comparison with WT. Moreover, overexpression of FcSISP in trifoliate orange [Poncirus trifoliata (L.) Raf.], a widely-used and salt-sensitive citrus rootstock, led to elevated salt tolerance. Taken together, the data demonstrate that FcSISP plays a positive role in salt tolerance and that it holds a great potential for engineering salt tolerance in crops.

Functional characterization of xanthoxin dehydrogenase in rice

Abscisic acid (ABA) is a phytohormone that plays a key role in biotic and abiotic stress responses. ABA metabolic genes are promising targets for molecular breeding work to improve stress tolerance in crops. The accumulation of ABA does not always improve stress tolerance since stress-induced accumulation of ABA in pollen inhibits the normal course of gametogenesis, affecting grain yields in cereals. This effect highlights the importance of manipulating the ABA levels according to the type of tissues. The aim of this study was to assign an ABA biosynthetic enzyme, xanthoxin dehydrogenase (XanDH), as a functional marker to modulate ABA levels in rice. XanDH is a member of the short-chain dehydrogenase/reductase family that catalyzes the conversion of xanthoxin to abscisyl aldehyde (ABAld). Previously, this enzyme had only been identified in Arabidopsis, as AtABA2. In this study, a XanDH named OsABA2 was identified in rice. Phylogenetic analysis indicated that a single gene encodes for OsABA2 in the rice genome. Its amino acid sequence contains two motifs that are essential for cofactor binding and catalytic activity. Expression analysis of OsABA2 mRNA showed that the transcript level did not change in response to treatment with ABA or dehydration. Recombinant OsABA2 protein expressed in Escherichia coli converted xanthoxin to ABAld in an NAD-dependent manner. Moreover, expression of OsABA2 in an Arabidopsis aba2 mutant rescued the aba2 mutant phenotypes, characterized by reduced growth, increased water loss, and germination in the presence of paclobutrazol, a gibberellin biosynthesis inhibitor or high concentration of glucose. These results indicate that OsABA2 is a rice XanDH that functions in ABA biosynthesis.

Linkage of cold acclimation and disease resistance through plant-pathogen interaction pathway in Vitis amurensis grapevine

Low temperatures cause severe damage to none cold hardy grapevines. A preliminary survey with Solexa sequencing technology was used to analyze gene expression profiles of cold hardy Vitis amurensis 'Zuoshan-1' after cold acclimation at 4 °C for 48 h. A total of 16,750 and 18,068 putative genes were annotated for 4 °C-treated and control library, respectively. Among them, 393 genes were upregulated for at least 20-fold, while 69 genes were downregulated for at least 20-fold under the 4 °C treatment for 48 h. A subset of 101 genes from this survey was investigated further using reverse transcription polymerase chain reaction (RT-PCR). Genes associated with signaling events in pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI), including generation of calcium signals (CNGC, CMLs), jasmonic acid signal (JAZ1), oxidative burst (Rboh), and phosphorylation (FLS2, BAK, MEKK1, MKKs) cascades, were upregulated after cold acclimation. Disease resistance genes (RPM1, RPS5, RIN4, PBS1) in the process of effector-triggered immunity (ETI) were also upregulated in the current condition. Defense-related genes (WRKYs, PR1, MIN7) involved in both PTI and ETI processes were abundantly expressed after cold acclimation. Our results indicated that plant-pathogen interaction pathways were linked to the cold acclimation in V. amurensis grapevine. Other biotic- and abiotic-related genes, such as defense (protein phosphatase 2C, U-box domain proteins, NCED1, stilbene synthase), transcription (DREBs, MYBs, ERFs, ZFPs), signal transduction (kinase, calcium, and auxin signaling), transport (ATP-binding cassette (ABC) transporters, auxin:hydrogen symporter), and various metabolism, were also abundantly expressed in the cold acclimation of V. Amurensis 'Zuoshan-1' grapevine. This study revealed a series of critical genes and pathways to delineate important biological processes affected by low temperature in 'Zuoshan-1'.