Candidate Genes For Drought Tolerance Research Articles

Rootstock-induced molecular responses associated with drought tolerance in sweet orange as revealed by RNA-Seq

BackgroundCitrus plants are commercially propagated by grafting, with the rootstock variety influencing a number of horticultural traits, including drought tolerance. Among the different rootstock varieties available for citrus propagation, ‘Rangpur’ lime is known to confer enhanced tolerance to drought as compared to other citrus rootstocks. The objective of this study was to investigate the poorly understood molecular responses underlying the rootstock-induced drought tolerance in sweet orange.ResultsRNA-Seq transcriptome analysis was carried out in leaves of sweet orange grafted on ‘Rangpur’ lime subjected to control and drought-stress treatments, under greenhouse conditions, using the Illumina HiSeq platform. A total of 41,827 unique transcripts were identified, among which 1764 transcripts showed significant variation (P ≤ 0.001) between the treatments, with 1081 genes induced and 683 repressed by drought-stress treatment. The transcripts were distributed in 44 different categories of cellular component, molecular function and biological process. Several genes related to cell metabolism, including those involved in the metabolisms of cell wall, carbohydrates and antioxidants, light reactions, biotic and abiotic stress responses, as well as genes coding for transcription factors (TFs), protein kinases (PKs) and proteins involved in the abscisic acid (ABA) and ethylene signaling pathways, were differentially regulated by drought stress. RNA-Seq data were validated by quantitative real-time PCR (qPCR) analysis and comparative analysis of expression of the selected genes between sweet orange grafted on drought-tolerant and -sensitive rootstocks revealed new candidate genes for drought tolerance in citrus.ConclusionsIn conclusion, our results showed that only a relatively small but functionally diverse fraction of the sweet orange transcriptome, with functions in metabolism, cellular responses and regulation, was differentially regulated by drought stress. The data suggest that the rootstock-induced drought tolerance in sweet orange includes the transcriptional activation of genes related to the cell wall, soluble carbohydrate and antioxidant metabolisms, biotic and abiotic stress responses, TFs, PKs and ABA signaling pathway, and the downregulation of genes involved in the starch metabolism, light reactions and ethylene signaling. Future efforts to elucidate their functional roles and explore their potential in the citrus genetic improvement should benefit from this data.

In silico Mining of EST-SSRs from the Drought Tolerant ESTs in Safflower

Drought stress is a major abiotic factor causing yield loss in safflower and limited studies have been carried out to dissect the molecular mechanism at EST-SSR level. In this study, a possible relationship between simple sequence repeats (SSRs) distribution and drought stress was studied using three EST libraries of safflower, Ct-D-EST, Ct-NEST and Co-EST. The Ct-D-EST was generated from drought tolerant safflower cultivar A-1; Ct-N-EST and Co-EST were the EST datasets of safflower and its wild progenitor C. oxycanthus, respectively. In total, 156 (45%), 1194 (5%) and 1550 (9%) EST-SSRs were mined from Ct-D-EST, Ct-N-EST and Co-EST libraries, respectively. Comparison of EST-SSRs from Ct-D-EST with that of SSRs from other two libraries showed reasonable differences for each class of repeats. Large variations were observed for dinucleotide repeats in all the libraries. In drought EST-SSRs, only one kind of amino acid was produced by repeat (ATG)14 which encodes met indicating the loci and repeat observed to be 100%. Since three ESTs with SSRs from Ct-D-EST, annotated to putative candidate genes, S-adenosylmethionine synthetase, one-helix protein and myo-inositol 1-phosphate synthetase, did not express with SSRs in the Ct-N-EST, these can be considered as potential candidate genes for drought tolerance. A trinuceotinde SSR, encoding met, was also found in the EST annotated to putative s-adenosylmethionine synthetase, hence, both can be considered as indices for drought tolerance. The genomic resources and the information generated in this study may be useful for the safflower breeders particularly for the development of drought tolerant cultivar.

Transcriptomic analysis of sweet potato under dehydration stress identifies candidate genes for drought tolerance.

Sweet potato (Ipomoea batatas [L.] Lam.) is an important subsistence crop in Sub‐Saharan Africa, yet as for many crops, yield can be severely impacted by drought stress. Understanding the genetic mechanisms that control drought tolerance can facilitate the development of drought‐tolerant sweet potato cultivars. Here, we report an expression profiling study using the US‐bred cultivar, Beauregard, and a Ugandan landrace, Tanzania, treated with polyethylene glycol (PEG) to simulate drought and sampled at 24 and 48 hr after stress. At each time‐point, between 4,000 to 6,000 genes in leaf tissue were differentially expressed in each cultivar. Approximately half of these differentially expressed genes were common between the two cultivars and were enriched for Gene Ontology terms associated with drought response. Three hundred orthologs of drought tolerance genes reported in model species were identified in the Ipomoea trifida reference genome, of which 122 were differentially expressed under at least one experimental condition, constituting a list of drought tolerance candidate genes. A subset of genes was differentially regulated between Beauregard and Tanzania, representing genotype‐specific responses to drought stress. The data analyzed and reported here provide a resource for geneticists and breeders toward identifying and utilizing drought tolerance genes in sweet potato.

Transcriptome Analyses in Different Cucumber Cultivars Provide Novel Insights into Drought Stress Responses.

Drought stress is one of the most serious threats to cucumber quality and yield. To gain a good understanding of the molecular mechanism upon water deficiency, we compared and analyzed the RNA sequencing-based transcriptomic responses of two contrasting cucumber genotypes, L-9 (drought-tolerant) and A-16 (drought-sensitive). In our present study, combining the analysis of phenotype, twelve samples of cucumber were carried out a transcriptomic profile by RNA-Seq under normal and water-deficiency conditions, respectively. A total of 1008 transcripts were differentially expressed under normal conditions (466 up-regulated and 542 down-regulated) and 2265 transcripts under drought stress (979 up-regulated and 1286 down-regulated). The significant positive correlation between RNA sequencing data and a qRT-PCR analysis supported the results found. Differentially expressed genes (DEGs) involved in metabolic pathway and biosynthesis of secondary metabolism were significantly changed after drought stress. Several genes, which were related to sucrose biosynthesis (Csa3G784370 and Csa3G149890) and abscisic acid (ABA) signal transduction (Csa4M361820 and Csa6M382950), were specifically induced after 4 days of drought stress. DEGs between the two contrasting cultivars identified in our study provide a novel insight into isolating helpful candidate genes for drought tolerance in cucumber.

Nucleotide Diversity of the Coding and Promoter Regions of DREB1D, a Candidate Gene for Drought Tolerance in Coffea Species

Climate change is posing a major challenge to coffee production worldwide leading to a need for the development of coffee cultivars with increased drought tolerance. In several plant species, the use of DREB genes in crop improvement has achieved promising results to desiccation tolerance engineering. Recent studies reported CcDREB1D specific patterns of expression in Coffea canephora and functional evidence of this gene involvement in drought stress responses. However, knowledge on natural diversity of this gene is largely unknown. In this context, this study aimed at evaluating the sequence variability of the DREB1D gene in several Coffea genotypes. Nucleotide variation in promoters and coding regions of this gene were evaluated in a population consisting of 38 genotypes of C. canephora, C. arabica and C. eugenioides, most of them characterized by different phenotypes (tolerance vs. susceptibility) in relation to drought. The genetic diversity of the loci revealed different haplotypes for the promoter and coding regions. In particular, our findings suggest association between drought tolerance and the genetic variations on DREB1D promoter regions, but not with those from its corresponding coding regions. Gene expression studies revealed up-regulated expression of DREB1D gene upon drought mainly in leaves of drought-tolerant clones of C. canephora, and in response to drought, high, and low temperatures in leaves of C. arabica, suggesting a key role of this gene in coffee responses to abiotic stress.

An integrated and comparative approach towards identification, characterization and functional annotation of candidate genes for drought tolerance in sorghum (Sorghum bicolor (L.) Moench)

BackgroundDrought is the most disastrous abiotic stress that severely affects agricultural productivity worldwide. Understanding the biological basis of drought-regulated traits, requires identification and an in-depth characterization of genetic determinants using model organisms and high-throughput technologies. However, studies on drought tolerance have generally been limited to traditional candidate gene approach that targets only a single gene in a pathway that is related to a trait. In this study, we used sorghum, one of the model crops that is well adapted to arid regions, to mine genes and define determinants for drought tolerance using drought expression libraries and RNA-seq data.ResultsWe provide an integrated and comparative in silico candidate gene identification, characterization and annotation approach, with an emphasis on genes playing a prominent role in conferring drought tolerance in sorghum. A total of 470 non-redundant functionally annotated drought responsive genes (DRGs) were identified using experimental data from drought responses by employing pairwise sequence similarity searches, pathway and interpro-domain analysis, expression profiling and orthology relation. Comparison of the genomic locations between these genes and sorghum quantitative trait loci (QTLs) showed that 40% of these genes were co-localized with QTLs known for drought tolerance. The genome reannotation conducted using the Program to Assemble Spliced Alignment (PASA), resulted in 9.6% of existing single gene models being updated. In addition, 210 putative novel genes were identified using AUGUSTUS and PASA based analysis on expression dataset. Among these, 50% were single exonic, 69.5% represented drought responsive and 5.7% were complete gene structure models. Analysis of biochemical metabolism revealed 14 metabolic pathways that are related to drought tolerance and also had a strong biological network, among categories of genes involved. Identification of these pathways, signifies the interplay of biochemical reactions that make up the metabolic network, constituting fundamental interface for sorghum defence mechanism against drought stress.ConclusionsThis study suggests untapped natural variability in sorghum that could be used for developing drought tolerance. The data presented here, may be regarded as an initial reference point in functional and comparative genomics in the Gramineae family.

Expansion of the dehydrin gene family in the Pinaceae is associated with considerable structural diversity and drought-responsive expression.

Temperatures are expected to increase over the next century in all terrestrial biomes and particularly in boreal forests, where drought-induced mortality has been predicted to rise. Genomics research is helping to develop hypotheses regarding the molecular basis of drought tolerance and recent work proposed that the osmo-protecting dehydrin proteins have undergone a clade-specific expansion in the Pinaceae, a major group of conifer trees. The objectives of this study were to identify all of the putative members of the gene family, trace their evolutionary origin, examine their structural diversity and test for drought-responsive expression. We identified 41 complete dehydrin coding sequences in Picea glauca, which is four times more than most angiosperms studied to date, and more than in pines. Phylogenetic reconstructions indicated that the family has undergone an expansion in conifers, with parallel evolution implicating the sporadic resurgence of certain amino acid sequence motifs, and a major duplication giving rise to a clade specific to the Pinaceae. A variety of plant dehydrin structures were identified with variable numbers of the A-, E-, S- and K-segments and an N-terminal (N1) amino acid motif including assemblages specific to conifers. The expression of several of the spruce dehydrins was tissue preferential under non-stressful conditions or responded to water stress after 7-18 days without watering, reflecting changes in osmotic potential. We found that dehydrins with N1 K2 and N1 AESK2 sequences were the most responsive to the lack of water. Together, the family expansion, drought-responsive expression and structural diversification involving loss and gain of amino acid motifs suggests that subfunctionalization has driven the diversification seen among dehydrin gene duplicates. Our findings clearly indicate that dehydrins represent a large family of candidate genes for drought tolerance in spruces and in other Pinaceae that may underpin adaptability in spatially and temporally variable environments.

Dehydration induced transcriptomic responses in two Tibetan hulless barley (Hordeum vulgare var. nudum) accessions distinguished by drought tolerance

BackgroundThe harsh environment on the Qinghai-Tibetan Plateau gives Tibetan hulless barley (Hordeum vulgare var. nudum) great ability to resist adversities such as drought, salinity, and low temperature, and makes it a good subject for the analysis of drought tolerance mechanism. To elucidate the specific gene networks and pathways that contribute to its drought tolerance, and for identifying new candidate genes for breeding purposes, we performed a transcriptomic analysis using two accessions of Tibetan hulless barley, namely Z772 (drought-tolerant) and Z013 (drought-sensitive).ResultsThere were more up-regulated genes of Z772 than Z013 under both mild (5439-VS-2604) and severe (7203-VS-3359) dehydration treatments. Under mild dehydration stress, the pathways exclusively enriched in drought-tolerance genotype Z772 included Protein processing in endoplasmic reticulum, tricarboxylic acid (TCA) cycle, Wax biosynthesis, and Spliceosome. Under severe dehydration stress, the pathways that were mainly enriched in Z772 included Carbon fixation in photosynthetic organisms, Pyruvate metabolism, Porphyrin and chlorophyll metabolism. The main differentially expressed genes (DEGs) in response to dehydration stress and genes whose expression was different between tolerant and sensitive genotypes were presented in this study, respectively. The candidate genes for drought tolerance were selected based on their expression patterns.ConclusionsThe RNA-Seq data obtained in this study provided an initial overview on global gene expression patterns and networks that related to dehydration shock in Tibetan hulless barley. Furthermore, these data provided pathways and a targeted set of candidate genes that might be essential for deep analyzing the molecular mechanisms of plant tolerance to drought stress.

SNP discovery in candidate genes for drought tolerance in barley (Hordeum vulgare L.) and genotyping using high-resolution melting analysis

Drought is one of the major environmental factors negatively affecting cultivated crop species. Thirty-one candidate genes for drought tolerance in barley were selected using a literature survey. SNP discovery was performed by aligning the corresponding nucleotide sequences of each candidate gene and SNPs with a base change from A/T to C/G or vice versa were selected. Primer pairs were designed to flank the selected SNPs. Using HRM analysis, all these markers showed polymorphism among 10 examined cultivars. The polymorphic information content (PIC) value of SNP markers ranged from 0.164 to 0.5, with a mean value of 0.307. Genetic diversity analysis of the HRM-SNPs data using UPGMA clustering grouped the studied barley cultivars into two clusters according to their drought tolerance. The first cluster encompassed the seven drought-tolerant cultivars and the second cluster contained drought-susceptible cultivars. In conclusion, HRM analysis is an effective method for SNPs genotyping and gene-based SNPs are particularly attractive for candidate gene-based association analyses, QTL mapping and functional diversity.

Insight into the AP2/ERF transcription factor superfamily in sesame and expression profiling of DREB subfamily under drought stress

BackgroundSesame is an important oilseed crop mainly grown in inclement areas with high temperatures and frequent drought. Thus, drought constitutes one of the major constraints of its production. The AP2/ERF is a large family of transcription factors known to play significant roles in various plant processes including biotic and abiotic stress responses. Despite their importance, little is known about sesame AP2/ERF genes. This constitutes a limitation for drought-tolerance candidate genes discovery and breeding for tolerance to water deficit.ResultsOne hundred thirty-two AP2/ERF genes were identified in the sesame genome. Based on the number of domains, conserved motifs, genes structure and phylogenetic analysis including 5 relatives species, they were classified into 24 AP2, 41 DREB, 61 ERF, 4 RAV and 2 Soloist. The number of sesame AP2/ERF genes was relatively few compared to that of other relatives, probably due to gene loss in ERF and DREB subfamilies during evolutionary process. In general, the AP2/ERF genes were expressed differently in different tissues but exhibited the highest expression levels in the root. Mostly all DREB genes were responsive to drought stress. Regulation by drought is not specific to one DREB group but depends on the genes and the group A6 and A1 appeared to be more actively expressed to cope with drought.ConclusionsThis study provides insights into the classification, evolution and basic functional analysis of AP2/ERF genes in sesame which revealed their putative involvement in multiple tissue-/developmental stages. Out of 20 genes which were significantly up- /down-regulated under drought stress, the gene AP2si16 may be considered as potential candidate gene for further functional validation as well for utilization in sesame improvement programs for drought stress tolerance.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0859-4) contains supplementary material, which is available to authorized users.

Identification of candidate genes for drought tolerance in coffee by high-throughput sequencing in the shoot apex of different Coffea arabica cultivars.

BackgroundDrought is a widespread limiting factor in coffee plants. It affects plant development, fruit production, bean development and consequently beverage quality. Genetic diversity for drought tolerance exists within the coffee genus. However, the molecular mechanisms underlying the adaptation of coffee plants to drought are largely unknown. In this study, we compared the molecular responses to drought in two commercial cultivars (IAPAR59, drought-tolerant and Rubi, drought-susceptible) of Coffea arabica grown in the field under control (irrigation) and drought conditions using the pyrosequencing of RNA extracted from shoot apices and analysing the expression of 38 candidate genes.ResultsPyrosequencing from shoot apices generated a total of 34.7 Mbp and 535,544 reads enabling the identification of 43,087 clusters (41,512 contigs and 1,575 singletons). These data included 17,719 clusters (16,238 contigs and 1,575 singletons) exclusively from 454 sequencing reads, along with 25,368 hybrid clusters assembled with 454 sequences. The comparison of DNA libraries identified new candidate genes (n = 20) presenting differential expression between IAPAR59 and Rubi and/or drought conditions. Their expression was monitored in plagiotropic buds, together with those of other (n = 18) candidates genes. Under drought conditions, up-regulated expression was observed in IAPAR59 but not in Rubi for CaSTK1 (protein kinase), CaSAMT1 (SAM-dependent methyltransferase), CaSLP1 (plant development) and CaMAS1 (ABA biosynthesis). Interestingly, the expression of lipid-transfer protein (nsLTP) genes was also highly up-regulated under drought conditions in IAPAR59. This may have been related to the thicker cuticle observed on the abaxial leaf surface in IAPAR59 compared to Rubi.ConclusionsThe full transcriptome assembly of C. arabica, followed by functional annotation, enabled us to identify differentially expressed genes related to drought conditions. Using these data, candidate genes were selected and their differential expression profiles were confirmed by qPCR experiments in plagiotropic buds of IAPAR59 and Rubi under drought conditions. As regards the genes up-regulated under drought conditions, specifically in the drought-tolerant IAPAR59, several corresponded to orphan genes but also to genes coding proteins involved in signal transduction pathways, as well as ABA and lipid metabolism, for example. The identification of these genes should help advance our understanding of the genetic determinism of drought tolerance in coffee.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0777-5) contains supplementary material, which is available to authorized users.

Identification of loci contributing to maize drought tolerance in a genome-wide association study

Genome-wide association studies (GWAS) have been used widely to analyze the genetic control of complex traits in crops. In the present study, seven related phenotypic traits were analyzed in combination to study their association with 41,101 SNPs in 201 maize inbred lines that had been evaluated in seven environments (year/location combinations) under water-stressed (WS) or well-watered (WW) regimes. By comparing the association signals with a fixed P value, GWAS showed that the number of association signals identified varied among traits and in different environments. Data that were missing under the severe water stress treatment had a great impact on the results of this GWAS. A total of 206 significant SNPs were associated with 115 candidate genes for drought tolerance and related traits including final grain yield, total number of ears per plot, kernel number per row, plant height, anthesis-silking interval, days to anthesis (DtA), and days to silking (DtS). Among these, four genes were associated with at least two different related traits, and six genes associated with traits were detected in at least two environments under water stress. Nine candidate QTL identified by GWAS were also discovered, three of which co-located to a consensus QTL region meta-analyzed by linkage mapping for drought tolerance. Some regulatory genes related to abiotic stress responses might also make a strong contribution to drought tolerance. The comprehensive information presented here regarding consensus QTL combined with candidate genes derived from GWAS provides an important reference tool for improving maize drought tolerance.

Mosaic genetic differentiation along environmental and geographic gradients indicate divergent selection in a white pine species complex

We explored the role of isolation by environment in a white pine species complex: Pinus flexilis, Pinus strobiformis and Pinus ayacahuite distributed from Canada to Central America. We predict that species differentiation would match genetic structure of candidate genes associated with significant differences in climatic niche in the species complex. To test this prediction, we sequenced five candidate genes for drought tolerance and three housekeeping genes, in individuals from across the entire range of each species. We performed neutrality tests, estimated genetic differentiation and performed partial mantel correlations, to test for isolation by environment in the species complex. Our results show that different loci vary in degrees of genetic differentiation within species and contrast in patterns of differentiation among species. This is considered to be a mosaic pattern of genetic differentiation. There was also significant isolation by environment in candidate genes. P. flexilis was genetically differentiated for candidate genes and P. ayacahuite for housekeeping genes. There was also an overall pattern of shared ancestral polymorphism followed by independent evolution. Nonetheless, all loci together recovered groups that correspond to the recognized taxonomy. In conclusion, the pattern of isolation by environment in candidate genes support the idea of ecologically driven differentiation of this species complex, especially in the case of P. flexilis. The observed difference in housekeeping genes between P. strobiformis and P. ayacahuite can be due to limited gene flow. The mosaic pattern of differentiation suggests that speciation is recent and ecological differences could be a factor in the diversification of pines in North America.

Network Candidate Genes in Breeding for Drought Tolerant Crops.

Climate change leading to increased periods of low water availability as well as increasing demands for food in the coming years makes breeding for drought tolerant crops a high priority. Plants have developed diverse strategies and mechanisms to survive drought stress. However, most of these represent drought escape or avoidance strategies like early flowering or low stomatal conductance that are not applicable in breeding for crops with high yields under drought conditions. Even though a great deal of research is ongoing, especially in cereals, in this regard, not all mechanisms involved in drought tolerance are yet understood. The identification of candidate genes for drought tolerance that have a high potential to be used for breeding drought tolerant crops represents a challenge. Breeding for drought tolerant crops has to focus on acceptable yields under water-limited conditions and not on survival. However, as more and more knowledge about the complex networks and the cross talk during drought is available, more options are revealed. In addition, it has to be considered that conditioning a crop for drought tolerance might require the production of metabolites and might cost the plants energy and resources that cannot be used in terms of yield. Recent research indicates that yield penalty exists and efficient breeding for drought tolerant crops with acceptable yields under well-watered and drought conditions might require uncoupling yield penalty from drought tolerance.

Transcriptome Profiling of Wild Arachis from Water-Limited Environments Uncovers Drought Tolerance Candidate Genes.

Peanut (Arachis hypogaea L.) is an important legume cultivated mostly in drought-prone areas where its productivity can be limited by water scarcity. The development of more drought-tolerant varieties is, therefore, a priority for peanut breeding programs worldwide. In contrast to cultivated peanut, wild relatives have a broader genetic diversity and constitute a rich source of resistance/tolerance alleles to biotic and abiotic stresses. The present study takes advantage of this diversity to identify drought-responsive genes by analyzing the expression profile of two wild species, Arachis duranensis and Arachis magna (AA and BB genomes, respectively), in response to progressive water deficit in soil. Data analysis from leaves and roots of A. duranensis (454 sequencing) and A. magna (suppression subtractive hybridization (SSH)) stressed and control complementary DNA (cDNA) libraries revealed several differentially expressed genes in silico, and 44 of them were selected for further validation by quantitative RT-PCR (qRT-PCR). This allowed the identification of drought-responsive candidate genes, such as Expansin, Nitrilase, NAC, and bZIP transcription factors, displaying significant levels of differential expression during stress imposition in both species. This is the first report on identification of differentially expressed genes under drought stress and recovery in wild Arachis species. The generated transcriptome data, besides being a valuable resource for gene discovery, will allow the characterization of new alleles and development of molecular markers associated with drought responses in peanut. These together constitute important tools for the peanut breeding program and also contribute to a better comprehension of gene modulation in response to water deficit and rehydration.Electronic supplementary materialThe online version of this article (doi:10.1007/s11105-015-0882-x) contains supplementary material, which is available to authorized users.

Identification of candidate genes for drought tolerance by whole-genome resequencing in maize

BackgroundDrought stress is one of the major limiting factors for maize production. With the availability of maize B73 reference genome and whole-genome resequencing of 15 maize inbreds, common variants (CV) and clustering analyses were applied to identify non-synonymous SNPs (nsSNPs) and corresponding candidate genes for drought tolerance.ResultsA total of 524 nsSNPs that were associated with 271 candidate genes involved in plant hormone regulation, carbohydrate and sugar metabolism, signaling molecules regulation, redox reaction and acclimation of photosynthesis to environment were detected by CV and cluster analyses. Most of the nsSNPs identified were clustered in bin 1.07 region that harbored six previously reported QTL with relatively high phenotypic variation explained for drought tolerance. Genes Ontology (GO) analysis of candidate genes revealed that there were 35 GO terms related to biotic stimulus and membrane-bounded organelle, showing significant differences between the candidate genes and the reference B73 background. Changes of expression level in these candidate genes for drought tolerance were detected using RNA sequencing for fertilized ovary, basal leaf meristem tissue and roots collected under drought stressed and well-watered conditions. The results indicated that 70% of candidate genes showed significantly expression changes under two water treatments and our strategies for mining candidate genes are feasible and relatively efficient.ConclusionsOur results successfully revealed candidate nsSNPs and associated genes for drought tolerance by comparative sequence analysis of 16 maize inbred lines. Both methods we applied were proved to be efficient for identifying candidate genes for complex traits through the next-generation sequencing technologies (NGS). These selected genes will not only facilitate understanding of genetic basis of drought stress response, but also accelerate genetic improvement through marker-assisted selection in maize.

Mapping of STS markers developed from drought tolerance candidate genes and preliminary analysis of their association with yield-related traits in common wheat(Triticum aestivum)

Drought is a severe abiotic stress that affects wheat production worldwide. In order to identify candidate genes for tolerance to water stress in wheat, sequences of 11 genes that have function of drought tolerance in other plant species were used to identify the wheat ortholog genes via homology searching in the wheat EST database. Atotal of 11 primer pairs were identified and amplified PCR products in wheat. Of them, 10 STS markers were mapped on 11 chromosomes in a set of nulli-tetrasomic lines of ‘Chinese Spring’ wheat; six were mapped on chromosomes 1A, 1B, 4B, 7A, 2B and 5D, respectively, in a spring wheat mapping population (POP1). The marker XTaABH1 mapped on 7A in POP1 was the only one mapped but characterized in a winter wheat mapping population (POP2) for grain yield, kernel weight and diameter, and height in four-field trials applied different water stress or irrigation. The marker XTaABH1 was significantly associated with grain yield under rainfed condition, with kernel weight under terminal stress and non-irrigation conditions, with kernel diameter and height under non-irrigated condition. The STS primers, map information and marker-trait association produced in the currently study would be of interest to researchers working on drought tolerance.

Identification of differentially-expressed genes potentially implicated in drought response in pitaya (Hylocereus undatus) by suppression subtractive hybridization and cDNA microarray analysis

Drought is one of the most severe threats to the growth, development and yield of plant. In order to unravel the molecular basis underlying the high tolerance of pitaya (Hylocereus undatus) to drought stress, suppression subtractive hybridization (SSH) and cDNA microarray approaches were firstly combined to identify the potential important or novel genes involved in the plant responses to drought stress. The forward (drought over drought-free) and reverse (drought-free over drought) suppression subtractive cDNA libraries were constructed using in vitro shoots of cultivar ‘Zihonglong’ exposed to drought stress and drought-free (control). A total of 2112 clones, among which half were from either forward or reverse SSH library, were randomly picked up to construct a pitaya cDNA microarray. Microarray analysis was carried out to verify the expression fluctuations of this set of clones upon drought treatment compared with the controls. A total of 309 expressed sequence tags (ESTs), 153 from forward library and 156 from reverse library, were obtained, and 138 unique ESTs were identified after sequencing by clustering and blast analyses, which included genes that had been previously reported as responsive to water stress as well as some functionally unknown genes. Thirty six genes were mapped to 47 KEGG pathways, including carbohydrate metabolism, lipid metabolism, energy metabolism, nucleotide metabolism, and amino acid metabolism of pitaya. Expression analysis of the selected ESTs by reverse transcriptase polymerase chain reaction (RT-PCR) corroborated the results of differential screening. Moreover, time-course expression patterns of these selected ESTs further confirmed that they were closely responsive to drought treatment. Among the differentially expressed genes (DEGs), many are related to stress tolerances including drought tolerance. Thereby, the mechanism of drought tolerance of this pitaya genotype is a very complex physiological and biochemical process, in which multiple metabolism pathways and many genes were implicated. The data gained herein provide an insight into the mechanism underlying the drought stress tolerance of pitaya, as well as may facilitate the screening of candidate genes for drought tolerance.

Association Mapping and Nucleotide Sequence Variation in Five Drought Tolerance Candidate Genes in Spring Wheat

Functional markers are needed for key genes involved in drought tolerance to improve selection for crop yield under moisture stress conditions. The objectives of this study were to (i) characterize five drought tolerance candidate genes, namely dehydration responsive element binding 1A (DREB1A), enhanced response to abscisic acid (ERA1‐B and ERA1‐D), and fructan 1‐exohydrolase (1‐FEH‐A and 1‐FEH‐B), in wheat (Triticum aestivum L.) for nucleotide and haplotype diversity, Tajima's D value, and linkage disequilibrium (LD) and (ii) associate within‐gene single nucleotide polymorphisms (SNPs) with phenotypic traits in a spring wheat association mapping panel (n = 126). Field trials were grown under contrasting moisture regimes in Greeley, CO, and Melkassa, Ethiopia, in 2010 and 2011. Genome‐specific amplification and DNA sequence analysis of the genes identified SNPs and revealed differences in nucleotide and haplotype diversity, Tajima's D, and patterns of LD. DREB1A showed associations (false discovery rate adjusted probability value = 0.1) with normalized difference vegetation index, heading date, biomass, and spikelet number. Both ERA1‐A and ERA1‐B were associated with harvest index, flag leaf width, and leaf senescence. 1‐FEH‐A was associated with grain yield, and 1‐FEH‐B was associated with thousand kernel weight and test weight. If validated in relevant genetic backgrounds, the identified marker–trait associations may be applied to functional marker‐assisted selection.

Analysis of drought tolerance candidate genes in transgenic plants

Analysis of drought tolerance candidate genes in transgenic plants