An A-6 subgroup member of DREB gene family positively regulates cold stress tolerance by modulating an antioxidant defense system in transgenic potato

Cold stress adversely influences the growth, development, geographic distribution, and yield of plants. The dehydration-responsive element binding (DREB) transcription factors are central to improving plant's ability to endure cold stress. In this work, the expression pattern of the StDREB30 (A-6) gene was analyzed in response to cold stress in transgenic potato. We provide evidence emphasizing the significance of the StDREB30 under low-temperature stress (4°C) and investigate the potential physiological, molecular and biochemical processes involved. StDREB30 expression levels were quickly elevated upon the cold exposure. Additionally, transgenic potato plants exhibited upregulation of randomly selected downstream genes (StNAC, StDREB1, StDREB2, StSAP, StGT3, and StDHN), improved photosynthetic parameters including coefficient of photochemical quenching (qL), and maximum yield of PSII (Fv'/Fm'), better stomatal performance, increased proline accumulation, decreased malondialdehyde content, electrolyte leakage, and reduced accumulation of hydrogen peroxide, and superoxide when exposed to cold stress. Moreover, StDREB30 improved reactive oxygen scavenging capabilities by stimulating the production of antioxidants such as superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase. Our results propose that StDREB30 serves as a positive regulator in promoting cold tolerance. To our knowledge, no report has been published previously on the study of the StDREB30 (A-6) gene under cold stress in transgenic potatoes.

Integrating gene expression analysis and ecophysiological responses to water deficit in leaves of tomato plants

Soil water deficit (WD) significantly impacts plant survival and crop yields. Many gaps remain in our understanding of the synergistic coordination between molecular and ecophysiological responses delaying substantial drought-induced effects on plant growth. To investigate this synergism in tomato leaves, we combined molecular, ecophysiological, and anatomical methods to examine gene expression patterns and physio-anatomical characteristics during a progressing WD experiment. Four sampling points were selected for transcriptomic analysis based on the key ecophysiological responses of the tomato leaves: 4 and 5 days after WD (d-WD), corresponding to 10% and 90% decrease in leaf stomatal conductance; 8 d-WD, the leaf wilting point; and 10 d-WD, when air embolism blocks 12% of the leaf xylem water transport. At 4 d-WD, upregulated genes were mostly linked to ABA-independent responses, with larger-scale ABA-dependent responses occurring at 5 d-WD. At 8 d-WD, we observed an upregulation of heat shock transcription factors, and two days later (10 d-WD), we found a strong upregulation of oxidative stress transcription factors. Finally, we found that young leaves present a stronger dehydration tolerance than mature leaves at the same drought intensity level, presumably because young leaves upregulate genes related to increased callose deposition resulting in limiting water loss to the phloem, and related to increased cell rigidity by modifying cell wall structures. This combined dataset will serve as a framework for future studies that aim to obtain a more holistic WD plant response at the molecular, ecophysiological and anatomical level.

Silencing of SlMYB78-like Reduces the Tolerance to Drought and Salt Stress via the ABA Pathway in Tomato

The MYB transcription factor family plays a crucial regulatory role in plant growth, development, biological progress, and stress responses. Here, we identified a R2R3-MYB transcription factor gene, SlMYB78-like, from tomato and characterized its function by gene silencing via RNA interference (RNAi). The results exhibited that the silencing of SlMYB78-like reduced the sensitivity of tomato seedlings to exogenous ABA. In addition, when exposed to drought and salt stresses, the RNAi lines grown in soil showed decreased tolerance, with lower ABA accumulation, relative water content, and chlorophyll content while displaying higher relative conductivity and malondialdehyde (MDA) content than the wild type. Moreover, the expression of genes related to chlorophyll biosynthesis, photosynthesis, and ABA biosynthesis/response were down-regulated in SlMYB78-like-silenced lines. Notably, the transcript level of SlCYP707-A2, which encodes a protein involved in ABA degradation, was up-regulated significantly after stresses. The transient expression assay Dual-luciferase (Dual-LUC) and a yeast one-hybrid (Y1H) assay demonstrated that SlMYB78-like bound to the promoter of SlCYP707-A2. Additionally, the physical interaction between SlMYB78-like and SlDREB3, which functioned in ABA signaling transduction, was identified through yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays. Collectively, our study illustrates that SlMYB78-like participates in the abiotic stress response via the ABA pathway.

A transcriptional regulation of ERF15 contributes to ABA-mediated cold tolerance in tomato

Cold stress is a major meteorological threat to crop growth and yield. Abscisic acid (ABA) plays important roles in plant cold tolerance by activating the expression of cold-responsive genes; however, the underlying transcriptional regulatory module remains unknown. Here, we demonstrated that the cold- and ABA-responsive transcription factor ETHYLENE RESPONSE FACTOR 15 (ERF15) positively regulates ABA-mediated cold tolerance in tomato. Exogenous ABA treatment significantly enhanced cold tolerance in wild-type tomato plants but failed to rescue erf15 mutants from cold stress. Transcriptome analysis showed that ERF15 was associated with the expression of cold-responsive transcription factors such as CBF1 and WRKY6. Further RT-qPCR assays confirmed that the ABA-induced increased in CBF1 and WRKY6 transcripts was suppressed in erf15 mutants when the plants were subjected to cold treatment. Moreover, yeast one-hybrid assays, dual-luciferase assays and electrophoretic mobility shift assays demonstrated that ERF15 activated the transcription of CBF1 and WRKY6 by binding their promoters. Silencing CBF1 or WRKY6 significantly decreased cold tolerance. Overall, our study identified the role of ERF15 in conferring ABA-mediated cold tolerance in tomato plants by activating CBF1 and WRKY6 expression. This study not only broadens our knowledge of the mechanism of ABA-mediated cold tolerance in plants but also highlights ERF15 as an ideal target gene for cold-tolerant crop breeding.

Molecular and physiological responses to salt stress in salinity-sensitive and tolerant Hibiscus rosa-sinensis cultivars

Ornamental plants are used to decorate urban and peri-urban areas, and during their cultivation or utilisation, they can be exposed to abiotic stress. Salinity is an abiotic stress factor that limits plant growth and reduces the ornamental value of sensitive species. In this study, transcriptomic analysis was conducted to identify genes associated with tolerance or sensitivity to salinity in two hibiscus (Hibiscus rosa-sinensis L.) cultivars, 'Porto' and 'Sunny wind'. The physiological and biochemical parameters of plants exposed to 50, 100, or 200 mM NaCl and water (control) were monitored. Salinity treatments were applied for six weeks. After four weeks, differences between cultivars were clearly evident and 'Porto' was more tolerant than 'Sunny wind'. The tolerant cultivar showed lower electrolyte leakage and ABA concentrations, and higher proline content in the leaves. Accumulation of Na in different organs was lower in the flower organs of 'Porto'. At the molecular level, several differential expressed genes were observed between the cultivars and flower organs. Among the highly expressed DEGs, coat protein, alcohol dehydrogenase, and AP2/EREBP transcription factor ERF-1. Among the downregulated genes, GH3 and NCED were the most interesting. The differential expression of these genes may explain the salt stress tolerance of 'Porto'.

Genome-wide identification, comprehensive characterization of transcription factors, cis-regulatory elements, protein homology, and protein interaction network of DREB gene family in Solanum lycopersicum

Tomato is a drought-sensitive crop which has high susceptibility to adverse climatic changes. Dehydration-responsive element-binding (DREB) are significant plant transcription factors that have a vital role in regulating plant abiotic stress tolerance by networking with DRE/CRT cis-regulatory elements in response to stresses. In this study, bioinformatics analysis was performed to conduct the genome-wide identification and characterization of DREB genes and promoter elements in Solanum lycopersicum. In genome-wide coverage, 58 SlDREB genes were discovered on 12 chromosomes that justified the criteria of the presence of AP2 domain as conserved motifs. Intron-exon organization and motif analysis showed consistency with phylogenetic analysis and confirmed the absence of the A3 class, thus dividing the SlDREB genes into five categories. Gene expansion was observed through tandem duplication and segmental duplication gene events in SlDREB genes. Ka/Ks values were calculated in ortholog pairs that indicated divergence time and occurrence of purification selection during the evolutionary period. Synteny analysis demonstrated that 32 out of 58 and 47 out of 58 SlDREB genes were orthologs to Arabidopsis and Solanum tuberosum, respectively. Subcellular localization predicted that SlDREB genes were present in the nucleus and performed primary functions in DNA binding to regulate the transcriptional processes according to gene ontology. Cis-acting regulatory element analysis revealed the presence of 103 motifs in 2.5-kbp upstream promoter sequences of 58 SlDREB genes. Five representative SlDREB proteins were selected from the resultant DREB subgroups for 3D protein modeling through the Phyre2 server. All models confirmed about 90% residues in the favorable region through Ramachandran plot analysis. Moreover, active catalytic sites and occurrence in disorder regions indicated the structural and functional flexibility of SlDREB proteins. Protein association networks through STRING software suggested the potential interactors that belong to different gene families and are involved in regulating similar functional and biological processes. Transcriptome data analysis has revealed that the SlDREB gene family is engaged in defense response against drought and heat stress conditions in tomato. Overall, this comprehensive research reveals the identification and characterization of SlDREB genes that provide potential knowledge for improving abiotic stress tolerance in tomato.

Biotechnological Interventions in Tomato (Solanum lycopersicum) for Drought Stress Tolerance: Achievements and Future Prospects

Tomato production is severely affected by abiotic stresses (drought, flood, heat, and salt) and causes approximately 70% loss in yield depending on severity and duration of the stress. Drought is the most destructive abiotic stress and tomato is very sensitive to the drought stress, as cultivated tomato lack novel gene(s) for drought stress tolerance. Only 20% of agricultural land worldwide is irrigated, and only 14.51% of that is well-irrigated, while the rest is rain fed. This scenario makes drought very frequent, which restricts the genetically predetermined yield. Primarily, drought disturbs tomato plant physiology by altering plant–water relation and reactive oxygen species (ROS) generation. Many wild tomato species have drought tolerance gene(s); however, their exploitation is very difficult because of high genetic distance and pre- and post-transcriptional barriers for embryo development. To overcome these issues, biotechnological methods, including transgenic technology and CRISPR-Cas, are used to enhance drought tolerance in tomato. Transgenic technology permitted the exploitation of non-host gene/s. On the other hand, CRISPR-Cas9 technology facilitated the editing of host tomato gene(s) for drought stress tolerance. The present review provides updated information on biotechnological intervention in tomato for drought stress management and sustainable agriculture.

SlDREB3, a negative regulator of ABA responses, controls seed germination, fruit size and the onset of ripening in tomato

SlDREB3 was identified as a ripening up-regulated gene of the AP2/ERF-domain family of transcription factors. Its manipulation affects processes primarily governed by ABA. It negatively regulates ABA responses in tomato by altering ABA levels/signaling and is, in turn, negatively regulated by ABA. SlDREB3 over-expression lines show higher transcript levels of the ABA metabolism genes CYP707A3 and UGT75C1 and an 85% reduction in ABA levels leading to early seed germination. In contrast, suppression lines show decreased CYP707A3/UGT75C1 expression, 3-fold higher ABA levels and delayed germination. The expression of other ABA signaling and response genes is also affected. Suppression of SlDREB3 accelerates the onset of ripening by 4-5 days while its over-expression delays it and also reduces final fruit size. SlDREB3 manipulation effects large scale changes in the fruit transcriptome with suppression lines showing early increase in ABA levels and activation of most ripening pathway genes that govern ethylene, carotenoids and softening. Strikingly, key transcription factors like CNR, NOR, RIN, FUL1, governing ethylene-dependent and ethylene-independent aspects of ripening, are activated early upon SlDREB3 suppression suggesting their control by ABA. The studies identify SlDREB3 as a negative regulator of ABA responses across tissues and a key ripening regulator controlling ethylene-dependent and ethylene-independent aspects.

Multidimensional Role of Silicon to Activate Resilient Plant Growth and to Mitigate Abiotic Stress

Sustainable agricultural production is critically antagonistic by fluctuating unfavorable environmental conditions. The introduction of mineral elements emerged as the most exciting and magical aspect, apart from the novel intervention of traditional and applied strategies to defend the abiotic stress conditions. The silicon (Si) has ameliorating impacts by regulating diverse functionalities on enhancing the growth and development of crop plants. Si is categorized as a non-essential element since crop plants accumulate less during normal environmental conditions. Studies on the application of Si in plants highlight the beneficial role of Si during extreme stressful conditions through modulation of several metabolites during abiotic stress conditions. Phytohormones are primary plant metabolites positively regulated by Si during abiotic stress conditions. Phytohormones play a pivotal role in crop plants' broad-spectrum biochemical and physiological aspects during normal and extreme environmental conditions. Frontline phytohormones include auxin, cytokinin, ethylene, gibberellin, salicylic acid, abscisic acid, brassinosteroids, and jasmonic acid. These phytohormones are internally correlated with Si in regulating abiotic stress tolerance mechanisms. This review explores insights into the role of Si in enhancing the phytohormone metabolism and its role in maintaining the physiological and biochemical well-being of crop plants during diverse abiotic stresses. Moreover, in-depth information about Si's pivotal role in inducing abiotic stress tolerance in crop plants through metabolic and molecular modulations is elaborated. Furthermore, the potential of various high throughput technologies has also been discussed in improving Si-induced multiple stress tolerance. In addition, a special emphasis is engrossed in the role of Si in achieving sustainable agricultural growth and global food security.

β-Cyclocitral, a Master Regulator of Multiple Stress-Responsive Genes in Solanum lycopersicum L. Plants

β-cyclocitral (βCC), a major apocarotenoid of β-carotene, enhances plants' defense against environmental stresses. However, the knowledge of βCC's involvement in the complex stress-signaling network is limited. Here we demonstrate how βCC reprograms the transcriptional responses that enable Solanum lycopersicum L. (tomato) plants to endure a plethora of environmental stresses. Comparative transcriptome analysis of control and βCC-treated tomato plants was done by generating RNA sequences in the BGISEQ-500 platform. The trimmed sequences were mapped on the tomato reference genome that identifies 211 protein-coding differentially expressed genes. Gene ontology and Kyoto Encyclopedia of Genes and Genomes analysis and their enrichment uncovered that only upregulated genes are attributed to the stress response. Moreover, 80% of the upregulated genes are functionally related to abiotic and biotic stresses. Co-functional analysis of stress-responsive genes revealed a network of 18 genes that code for heat shock proteins, transcription factors (TFs), and calcium-binding proteins. The upregulation of jasmonic acid (JA)-dependent TFs (MYC2, MYB44, ERFs) but not the JA biosynthetic genes is surprising. However, the upregulation of DREB3, an abscisic acid (ABA)-independent TF, validates the unaltered expression of ABA biosynthetic genes. We conclude that βCC treatment upregulates multiple stress-responsive genes without eliciting JA and ABA biosynthesis.

Development of 50 InDel-based barcode system for genetic identification of tartary buckwheat resources

Tartary buckwheat (Fagopyrum tataricum Gartn.) is a highly functional crop that is poised to be the target of many future breeding efforts. The reliable ex situ conservation of various genetic resources is essential for the modern breeding of tartary buckwheat varieties. We developed PCR-based co-dominant insertion/deletion (InDel) markers to discriminate tartary buckwheat genetic resources. First, we obtained the whole genome from 26 accessions across a superscaffold-scale reference genome of 569.37 Mb for tartary buckwheat cv. "Daegwan 3-7." Next, 171,926 homogeneous and 53,755 heterogeneous InDels were detected by comparing 26 accessions with the "Daegwan 3-7" reference sequence. Of these, 100 candidate InDels ranging from 5-20 bp in length were chosen for validation, and 50 of them revealed polymorphisms between the 26 accessions and "Daegwan 3-7." The validated InDels were further tested through the assessment of their likelihood to give rise to a single or a few PCR products in 50 other accessions, covering most tartary buckwheat genome types. The major allele frequencies ranged from 0.5616 at the TB42 locus to 0.9863 at the TB48 locus, with the average PIC value of 0.1532 with a range of 0.0267-0.3712. To create a user-friendly system, the homology of the genotypes between and among the accessions were visualized in both one- (1D) and two-dimensional (2D) barcode types by comparing amplicon polymorphisms with the reference variety, "Daegwan 3-7." A phylogenetic tree and population structure of the 76 accessions according to amplicon polymorphisms for the 50 InDel markers corresponded to those using non-synonymous single nucleotide polymorphism variants, indicating that the barcode system based on the 50 InDels was a useful tool to improve the reliability of identification of tartary buckwheat accessions in the germplasm stocks.

Jasmonic acid and ERF family genes are involved in chilling sensitivity and seed browning of pepper fruit after harvest

Pepper (Capsicum annuum L.) fruit is sensitive to temperatures below 10 °C, which severely diminish fruit quality during cold chain distribution. Seed browning was a major chilling symptom in 36 genotypes of C. annuum fruit screened after storage at 2 °C for 3 weeks. Among them, pepper fruits of chilling-insensitive 'UZB-GJG-1999-51' and -sensitive 'C00562' were treated at 2 °C for 0 or 24 h, respectively. Analyses of integrated transcriptome-metabolome and relative gene expression in seeds obtained from the two genotypes were conducted to identify key factors involved in the seed browning induced by chilling. The relative contents of branched-chain amino acids such as leucine, isoleucine, and valine were significantly increased after chilling. Transcriptome identification showed 3,140 differentially expressed genes (log twofold change > 1.0 and FDR-corrected p value < 0.05) affected by chilling between the two genotypes. Particularly, genes related to jasmonic acid synthesis and signaling were differentially expressed. A regulatory network of jasmonic acid synthesis and signaling, and regulation of ERF family genes might contribute to chilling response in pepper fruit. The results of this study may help facilitate further studies to develop chilling-insensitive peppers and could be a basis for improving postharvest fruit quality.

Expression of galactinol synthase from Ammopiptanthus nanus in tomato improves tolerance to cold stress

Soluble carbohydrates not only directly affect plant growth and development but also act as signal molecules in processes that enhance tolerance to cold stress. Raffinose family oligosaccharides (RFOs) are an example and play an important role in abiotic stress tolerance. This study aimed to determine whether galactinol, a key limiting factor in RFO biosynthesis, functions as a signal molecule in triggering cold tolerance. Exposure to low temperatures induces the expression of galactinol synthase (AnGolS1) in Ammopiptanthus nanus, a desert plant that survives temperatures between -30 °C to 47 °C. AnGolS1 has a greater catalytic activity than tomato galactinol synthase (SlGolS2). Moreover, SlGolS2 is expressed only at low levels. Expression of AnGolS1 in tomato enhanced cold tolerance and led to changes in the sugar composition of the seeds and seedlings. AnGolS1 transgenic tomato lines exhibited an enhanced capacity for ethylene (ET) signaling. The application of galactinol abolished the repression of the ET signaling pathway by 1-methylcyclopropene during seed germination. In addition, the expression of ERF transcription factors was increased. Galactinol may therefore act as a signal molecule affecting the ET pathway.

CaWRKY27 negatively regulates salt and osmotic stress responses in pepper

WRKY transcription factors are key regulatory components of plant responses to both biotic and abiotic stresses. In pepper (Capsicum annuum), CaWRKY27 positively regulates resistance to the pathogenic bacterium Ralstonia solanacearum and negatively regulates thermotolerance. Here, we report that CaWRKY27 functions in the response to salinity and osmotic stress. CaWRKY27 transcription was induced by salinity, osmotic, and abscisic acid (ABA) treatments, as determined using qPCR and GUS assays. Transgenic Arabidopsis thaliana and tobacco (Nicotiana tabacum) plants heterologously expressing CaWRKY27 had an increased sensitivity to salinity and osmotic stress, with a higher inhibition of both root elongation and whole plant growth, more severe chlorosis and wilting, lower germination rates, and an enhanced germination sensitivity to ABA than the corresponding wild-type plants. Furthermore, most marker genes associated with reactive oxygen species (ROS) detoxification and polyamine and ABA biosynthesis, as well as stress-responsive genes NtDREB3, were downregulated in plants transgenically expressing CaWRKY27 upon exposure to salinity or osmotic stress. Consistently, silencing of CaWRKY27 using virus-induced gene silencing conferred tolerance to salinity and osmotic stress in pepper plants. These findings suggest that CaWRKY27 acts as a molecular link in the antagonistic crosstalk regulating the expression of defense-related genes in the responses to both abiotic and biotic stresses by acting either as a transcriptional activator or repressor in pepper.

Identifying resurrection genes through the differentially expressed genes between Selaginella tamariscina (Beauv.) spring and Selaginella moellendorffii Hieron under drought stress

Selaginella tamariscina (Beauv.) spring, a primitive vascular resurrection plant, can survive extreme drought and recover when water becomes available. To identify drought-inducible genes and to clarify the molecular mechanism of drought tolerance, a comparative transcriptional pattern analysis was conducted between S. tamariscina and Selaginella moellendorffii Hieron (drought sensitive). 133 drought related genes were identified, including 72 functional genes and 61 regulatory genes. And several drought responsive reactions, such as antioxidant activity, osmotic balance, cuticle defense and signal transduction were highlighted in S. tamariscina under drought. Notably, besides peroxidase, catalase and L-ascorbate oxidase genes, DEGs associated with phenylalanine metabolism and polyamine catabolism could be alternative ways to enhance antioxidant ability in S. tamariscina. DEGs related to soluble carbohydrate metabolism, late embryogenesis abundant protein (LEA) and aquaporin protein (AQP) confirmed that osmotic adjustment could resist drought during desiccation. DEGs involved in xyloglucan metabolic process, pectin metabolic process and cutin biosynthesis may also contribute to drought tolerance of S. tamariscina by cuticle defense. Drought-responsive genes encoding protein kinases, calcium sensors, transcription factors (TFs) and plant hormones also help to drought resistance of S. tamariscina. The preliminary validation experiments were performed and the results were consistent with our hypothetical integrated regulatory network. The results of this study provide candidate resurrection genes and an integrated regulatory network for further studies on the molecular mechanisms of stress tolerance in S. tamariscina.

A tomato transcription factor, SlDREB3 enhances the tolerance to chilling in transgenic tomato

The dehydration response factor (DREB) transcription factor (TF) family can function in response to multiple cues around environment in plants. Nevertheless, the functions of dehydration response factor (DREB protein) in plant cold tolerance, especially in tomatoes (Solanum lycopersicum), have been rarely studied. In this study, the functions of tomato DREB TF (SlDREB3) in cold resistance were studied using transgenic tomatoes. The level of transcripts revealed that SlDREB3 was triggered by H₂O₂ and 4 °C treatments, indicating that SlDREB3 participates in response to cold stress in plants. SlDREB3-overexpressing plants exhibited high fresh mass, chlorophyll content, Fv/Fm, and O₂-evolving activity; low membrane damage; and reactive oxygen species accumulation under chilling stress. Furthermore, the high expression levels of late embryogenesis-abundant genes SlLEA9 and SlLEA26 were detected in transgenic plants in response to cold stress. These findings revealed that SlDREB3 overexpression improved the tolerance to cold stress in transgenic plants possibly by upregulating SlLEAs expression.

Analysis of Drought Tolerance and Associated Traits in Upland Cotton at the Seedling Stage

(1) Background: Upland cotton (Gossypium hirsutum L.) is the most important natural fiber worldwide, and it is extensively planted and plentifully used in the textile industry. Major cotton planting regions are frequently affected by abiotic stress, especially drought stress. Drought resistance is a complex, quantitative trait. A genome-wide association study (GWAS) constitutes an efficient method for dissecting the genetic architecture of complex traits. In this study, the drought resistance of a population of 316 upland cotton accessions was studied via GWAS. (2) Methods: GWAS methodology was employed to identify relationships between molecular markers or candidate genes and phenotypes of interest. (3) Results: A total of 8, 3, and 6 SNPs were associated with the euphylla wilting score (EWS), cotyledon wilting score (CWS), and leaf temperature (LT), respectively, based on a general linear model and a factored spectrally transformed linear mixed model. For these traits, 7 QTLs were found, of which 2 each were located on chromosomes A05, A11, and D03, and of which 1 was located on chromosome A01. Importantly, in the candidate regions WRKY70, GhCIPK6, SnRK2.6, and NET1A, which are involved in the response to abscisic acid (ABA), the mitogen-activated protein kinase (MAPK) signaling pathway and the calcium transduction pathway were identified in upland cotton at the seedling stage under drought stress according to annotation information and linkage disequilibrium (LD) block analysis. Moreover, RNA sequencing analysis showed that WRKY70, GhCIPK6, SnRK2.6, and NET1A were induced by drought stress, and the expression of these genes was significantly different between normal and drought stress conditions. (4) Conclusions: The present study should provide some genomic resources for drought resistance in upland cotton. Moreover, the germplasm of the different phenotypes, the detected SNPs and, the potential candidate genes will be helpful for molecular marker-assisted breeding studies about increased drought resistance in upland cotton.

The Genome Sequence of the Wild Tomato Solanum pimpinellifolium Provides Insights Into Salinity Tolerance

Solanum pimpinellifolium, a wild relative of cultivated tomato, offers a wealth of breeding potential for desirable traits such as tolerance to abiotic and biotic stresses. Here, we report the genome assembly and annotation of S. pimpinellifolium 'LA0480.' Moreover, we present phenotypic data from one field experiment that demonstrate a greater salinity tolerance for fruit- and yield-related traits in S. pimpinellifolium compared with cultivated tomato. The 'LA0480' genome assembly size (811 Mb) and the number of annotated genes (25,970) are within the range observed for other sequenced tomato species. We developed and utilized the Dragon Eukaryotic Analyses Platform (DEAP) to functionally annotate the 'LA0480' protein-coding genes. Additionally, we used DEAP to compare protein function between S. pimpinellifolium and cultivated tomato. Our data suggest enrichment in genes involved in biotic and abiotic stress responses. To understand the genomic basis for these differences in S. pimpinellifolium and S. lycopersicum, we analyzed 15 genes that have previously been shown to mediate salinity tolerance in plants. We show that S. pimpinellifolium has a higher copy number of the inositol-3-phosphate synthase and phosphatase genes, which are both key enzymes in the production of inositol and its derivatives. Moreover, our analysis indicates that changes occurring in the inositol phosphate pathway may contribute to the observed higher salinity tolerance in 'LA0480.' Altogether, our work provides essential resources to understand and unlock the genetic and breeding potential of S. pimpinellifolium, and to discover the genomic basis underlying its environmental robustness.

Signatures of natural selection in abiotic stress-responsive genes of Solanum chilense

Environmental conditions are strong selective forces, which may influence adaptation and speciation. The wild tomato species Solanum chilense, native to South America, is exposed to a range of abiotic stress factors. To identify signatures of natural selection and local adaptation, we analysed 16 genes involved in the abiotic stress response and compared the results to a set of reference genes in 23 populations across the entire species range. The abiotic stress-responsive genes are characterized by elevated nonsynonymous nucleotide diversity and divergence. We detected signatures of positive selection in several abiotic stress-responsive genes on both the population and species levels. Local adaptation to abiotic stresses is particularly apparent at the boundary of the species distribution in populations from coastal low-altitude and mountainous high-altitude regions.

Ectopic expression of a tomato DREB gene affects several ABA processes and influences plant growth and root architecture in an age-dependent manner

Regulation of whole plant growth and adaptive responses by abscisic acid is complex, requires multiple regulators and largely unknown in plants other than Arabidopsis. We show that over-expression of the tomato SlDREB3/SlERF.H12 (DEHYDRATION RESPONSE ELEMENT BINDING PROTEIN3/ETHYLENE RESPONSE FACTOR. H12) gene can negatively affect many ABA-governed processes across tissues. Its expression leads to early germination in presence of ABA and in response to mannitol, NaCl and glucose. Its expression delays ABA-mediated leaf senescence and natural senescence leading to an increase in plant life by about 20days. Transgenic SlDREB3 lines show reduced ABA-mediated inhibition of conductance and transpiration and a greater sensitivity to water stress. Reduction in sensitivity to ABA-mediated stomatal closure leads to higher photosynthetic rates in transgenic plants than controls. Consequently, transgenic SlDREB3 plants produce a larger number of capsules and greater number of seeds with the increase in yield ranging from 18 to 35% in different seasons under well-watered conditions. Root growth, but not shoot growth, also undergoes a profound increase of about 50% in transgenic SlDREB3 lines. The increase occurs in an age-dependent manner with the most prominent changes being observed between 1.5 and 2.5 months in several independent experiments in different years. SlDREB3 thus seems to govern several ABA-regulated processes across tissues, partly through control over ABA levels. It may encode a factor that is most likely a component of the central ABA response machinery.

Transcriptional Analyses of Mandarins Seriously Infected by 'Candidatus Liberibacter asiaticus'

A range of leaf symptoms, including blotchy mottle, yellowing, and small, upright leaves with a variety of chlorotic patterns resembling those induced by zinc deficiencies, are associated with huanglongbing (HLB, yellow shoot disease), a worldwide destructive citrus disease. HLB is presumably caused by the phloem-limited fastidious prokaryotic α-proteobacterium ‘Candidatus Liberibacter spp.’ Previous studies focused on the proteome and transcriptome analyses of citrus 5 to 35 weeks after ‘Ca. L. spp.’ inoculation. In this study, gene expression profiles were analyzed from mandarin Citrus reticulate Blanco cv. jiaogan leaves after a 2 year infection with ‘Ca. L. asiaticus’. The Affymetrix microarray analysis explored 2,017 differentially expressed genes. Of the 1,364 genes had known functions, 938 (46.5%) were up-regulated. Genes related to photosynthesis, carbohydrate metabolic, and structure were mostly down-regulated, with rates of 92.7%, 61.0%, and 80.2%, respectively. Genes associated with oxidation-reduction and transport were mostly up-regulated with the rates of 75.0% and 64.6%, respectively. Our data analyses implied that the infection of ‘Ca. L. asiaticus’ could alter hormone crosstalk, inducing the jasmine acid pathway and depressing the ethylene and salicylic acid pathways in the citrus host. This study provides an enhanced insight into the host response of citrus to ‘Ca. L. asiaticus’ infection at a two-years infection stage.

Molecular and physiological dissection of enhanced seed germination using short-term low-concentration salt seed priming in tomato

Seed germination is the initial step of plant development. Seed priming with salt promotes seed germination in tomato (Solanum lycopersicum L.); however, the molecular and physiological mechanisms underlying the enhancement of seed germination by priming remain to be elucidated. In this study, we examined the following in seeds both during and after priming treatment: the endogenous abscisic acid (ABA) and gibberellin (GA) concentrations; the expression of genes encoding ABA catabolic and GA biosynthesis enzymes, including 8'-hydroxylase (CYP707A), copalyl diphosphate synthase (CPS), GA 20-oxidase (GA20ox) and GA 3-oxidase (GA3ox); and endosperm cap weakening enzymes, including expansin (EXP), class I β-1,3-glucanase (GulB), endo-β-mannanase (MAN) and xyloglucan endotransglucosylase (XTH). Tomato seeds were soaked for 24 h at 25 °C in the dark in 300 mM NaCl (NaCl-priming) or distilled water (hydro-priming). For both priming treatments, the ABA content in the seeds increased during treatment but rapidly decreased after sowing. Both during and after the priming treatments, the ABA levels in the hydro-primed seeds and NaCl-primed seeds were not significantly different. The expression levels of SlGA20ox1, SlGA3ox1 and SlGA3ox2 were significantly enhanced in the NaCl-primed seeds compared to the hydro-primed seeds. The GA(4) content was quantifiable after both types of priming, indicating that GA(4) is the major bioactive GA molecule involved in tomato seed germination. The GA(4) content was significantly higher in the NaCl-primed seeds than in the hydro-primed seeds 12 h after sowing and thereafter. Additionally, the peak expression levels of SlEXP4, SlGulB, SlMAN2 and SlXTH4 occurred earlier and were significantly higher in the NaCl-primed seeds than in the hydro-primed seeds. These results suggest that the observed effect of NaCl-priming on tomato seed germination is caused by an increase of the GA(4) content via GA biosynthetic gene activation and a subsequent increase in the expression of genes related to endosperm cap weakening.

Reduced tillering in Basmati rice T-DNA insertional mutant OsTEF1 associates with differential expression of stress related genes and transcription factors

A T-DNA insertional mutant OsTEF1 of rice gives 60-80% reduced tillering, retarded growth of seminal roots, and sensitivity to salt stress compared to wild type Basmati 370. The insertion occurred in a gene encoding a transcription elongation factor homologous to yeast elf1, on chromosome 2 of rice. Detailed transcriptomic profiling of OsTEF1 revealed that mutation in the transcription elongation factor differentially regulates the expression of more than 100 genes with known function and finely regulates tillering process in rice by inducing the expression of cytochrome P450. Along with different transcription factors, several stress associated genes were also affected due to a single insertion. In silico analysis of the TEF1 protein showed high conservation among different organisms. This transcription elongation factor predicted to interact with other proteins that directly or indirectly positively regulate tillering in rice.

Over-expression of JcDREB, a putative AP2/EREBP domain-containing transcription factor gene in woody biodiesel plant Jatropha curcas, enhances salt and freezing tolerance in transgenic Arabidopsis thaliana

Jatropha curcas L. is an all-purpose biodiesel plant and is widely distributed in tropical and subtropical climates. It can grow well on poor quality soil which is not qualified for crop cultivation. This is very important for relieving land, food and energy crises. However, tropical and subtropical distribution limits the production of J. curcas seed. So it is valuable to know the molecular mechanism of J. curcas response to adverse abiotic environmental factors, especially freezing stress, in order to change the plant's characteristics. Until now there are just a few reports about J. curcas molecular biology. In this paper, we cloned and characterized a DNA binding protein from this plant, designated as JcDREB. Sequence analysis and yeast one-hybrid assays show that JcDREB can effectively function as a transcription factor of DREB protein family belonging to A-6 subgroup member. Expression patterns of JcDREB showed that it was induced by cold, salt and drought stresses, not by ABA. Over-expression of JcDREB in transgenic Arabidopsis exhibited enhanced salt and freezing stresses. Understanding the molecular mechanisms of J. curcas responses to environmental stresses, for example, high salinity, drought and low temperature, is crucial for improving their stress tolerance and productivity. This work provides more information about A-6 subgroup members of DREB subfamily.