Isolation and characterization of drought-responsive genes from peanut roots by suppression subtractive hybridization

Deep sequencing of suppression subtractive library identifies differentially expressed transcripts of Saccharum spontaneum exposed to salinity stress

Saccharum spontaneum, a wild relative of sugarcane, is highly tolerant to drought and salinity. The exploitation of germplasm resources for salinity tolerance is a major thrust area in India. In this study, we utilized suppression subtractive hybridization (SSH) followed by sequencing for the identification of upregulated transcripts during salinity stress in S. spontaneum clones coming from different geographical regions of India. Our sequencing of the SSH library revealed that 95% of the transformants contained inserts of size 200-1500 bp. We have identified 314 differentially expressed transcripts in the salinity-treated samples after subtraction, which were subsequently validated by quantitative real-time polymerase chain reaction. Functional annotation and pathway analysis revealed that the upregulated transcripts were a result of protein modifications, stress, and hormone signaling along with cell wall development and lignification. The prominently upregulated transcripts included UDP glucose dehydrogenase, cellulose synthase, ribulose, cellulose synthase COBRA, leucine-rich protein, NAC domain protein, pectin esterase, ABA-responsive element binding factor 1, and heat stress protein. Our results is a step forward the understanding of the molecular response of S. spontaneum under salinity stress, which will lead to the identification of genes and transcription factors as novel targets for salinity tolerance in sugarcane.

Proteomic profiling of Arachis hypogaea in response to drought stress and overexpression of AhLEA2 improves drought tolerance

Drought is the main factor restricting peanut growth, but the molecular mechanism underlying peanut drought tolerance remains unclear. Herein, the seedling stage of drought-resistant peanut cultivar J11 was subjected to drought stress, and its proteomic profile was systematically analysed by isobaric tags for relative and absolute quantification (iTRAQ), the results of which were further complemented with our previous transcriptome results. A total of 4,018 proteins were identified by proteomic analysis, which revealed that the expression levels of 69 proteins were altered under drought stress. Among the differentially expressed proteins (DEPs), 50 were upregulated, and 19 were downregulated. The most enriched metabolic pathways for these DEPs were those involving phenylpropanoid biosynthesis, flavonoid biosynthesis, and plant hormone signal transduction. The proteomic data and previous transcriptome results revealed 44 groups of genes/proteins with the same expression trend, including a LEA (Late embryogenesis abundant) gene, AhLEA2. Our present study showed that overexpression of the AhLEA2 gene enhanced the drought resistance of transgenic Arabidopsis plants, and the activities of related antioxidant enzymes in the transgenic plants significantly changed. The AhLEA2 gene was found to be located in the cytoplasm and cell membrane by subcellular localization experiments. This work systematically analysed the differentially expressed proteins in peanut in response to drought stress, providing important candidates for further functional analysis of the stress response of peanut. Our results also indicated that AhLEA2 plays an important role in the peanut response to drought stress.

Transcriptomic analysis reveals key transcription factors associated to drought tolerance in a wild papaya (Carica papaya) genotype

Most of the commercial papaya genotypes show susceptibility to water deficit stress and require high volumes of irrigation water to yield properly. To tackle this problem, we have collected wild native genotypes of Carica papaya that have proved to show better physiological performance under water deficit stress than the commercial cultivar grown in Mexico. In the present study, plants from a wild Carica papaya genotype and a commercial genotype were subjected to water deficit stress (WDS), and their response was characterized in physiological and molecular terms. The physiological parameters measured (water potential, photosynthesis, Fv/Fm and electrolyte leakage) confirmed that the papaya wild genotype showed better physiological responses than the commercial one when exposed to WDS. Subsequently, RNA-Seq was performed for 4 cDNA libraries in both genotypes (susceptible and tolerant) under well-watered conditions, and when they were subjected to WDS for 14 days. Consistently, differential expression analysis revealed that after 14 days of WDS, the wild tolerant genotype had a higher number of up-regulated genes, and a higher number of transcription factors (TF) that were differentially expressed in response to WDS, than the commercial genotype. Thus, six TF genes (CpHSF, CpMYB, CpNAC, CpNFY-A, CpERF and CpWRKY) were selected for further qRT-PCR analysis as they were highly expressed in response to WDS in the wild papaya genotype. qRT-PCR results confirmed that the wild genotype had higher expression levels (REL) in all 6 TF genes than the commercial genotype. Our transcriptomic analysis should help to unravel candidate genes that may be useful in the development of new drought-tolerant cultivars of this important tropical crop.

Molecular and Physiological Alterations in Chickpea under Elevated CO2 Concentrations

The present study reports profiling of the elevated carbon dioxide (CO2) concentration responsive global transcriptome in chickpea, along with a combinatorial approach for exploring interlinks between physiological and transcriptional changes, important for the climate change scenario. Various physiological parameters were recorded in two chickpea cultivars (JG 11 and KAK 2) grown in open top chambers under ambient [380 parts per million (ppm)] and two stressed/elevated CO2 concentrations (550 and 700 ppm), at different stages of plant growth. The elevated CO2 concentrations altered shoot and root length, nodulation (number of nodules), total chlorophyll content and nitrogen balance index, significantly. RNA-Seq from 12 tissues representing vegetative and reproductive growth stages of both cultivars under ambient and elevated CO2 concentrations identified 18,644 differentially expressed genes including 9,687 transcription factors (TF). The differential regulations in genes, gene networks and quantitative real-time polymerase chain reaction (qRT-PCR) -derived expression dynamics of stress-responsive TFs were observed in both cultivars studied. A total of 138 pathways, mainly involved in sugar/starch metabolism, chlorophyll and secondary metabolites biosynthesis, deciphered the crosstalk operating behind the responses of chickpea to elevated CO2 concentration.

Proline metabolic dynamics and implications in drought tolerance of peanut plants

Proline accumulation and metabolism are associated with mechanisms of abiotic stress avoidance in plants. Proline accumulation generally improves osmotic stress tolerance whereas proline metabolism can have varying effects from ATP generation to the formation of reactive oxygen species. To further understand the roles of proline in stress protection, two peanut cultivars with contrasting tolerance to drought were examined by transcriptional and biochemical analyses during water stress. Plants exposed to polyethylene glycol had diminished relative water content and increased proline content; while, only the drought sensitive plants, cultivar Granoleico, showed lipid oxidative damage (measured as thiobarbituric acid reactive substances). The expression of proline biosynthesis genes (P5CS1, P5CS2a, P5CS2b, P5CR) was increased in both cultivars upon exposure to water stress. However, the relative expression of proline catabolism genes (ProDH1, ProDH2) was increased only in the sensitive cultivar during stress. Exogenous addition of proline and the proline analogue thiazolidine-4-carboxylic acid (T4C), both substrates of proline dehydrogenase, was also used to exacerbate and identify plant responses. Pretreatment of plants with T4C induced unique changes in the drought tolerant EC-98 cultivar such as higher mRNA levels of proline biosynthetic and catabolic ProDH genes, even in the absence of water stress. The increased levels of ProDH gene expression, potentially associated with higher T4C conversion to cysteine, may contribute to the tolerant phenotype.

Transcriptomic analysis and discovery of genes in the response of Arachis hypogaea to drought stress

The peanut (Arachis hypogaea) is an important crop species that is threatened by drought stress. The genome sequences of peanut, which was officially released in 2016, may help explain the molecular mechanisms that underlie drought tolerance in this species. We report here a gene expression profiling of A. hypogaea to gain a global view of its drought resistance. Using whole-transcriptome sequencing, we analysed differential gene expression in response to drought stress in the drought-resistant peanut cultivar J11. Pooled samples obtained at 6, 12, 18, 24, and 48 h were compared with control samples at 0 h. In total, 51,554 genes were found, including 49,289 known genes and 2265 unknown genes. We identified 224 differentially expressed transcription factors, 296,335 SNPs and 28,391 InDELs. In addition, we detected significant differences in the gene expression profiles of the treatment and control groups. After comparing the two groups, 4648 genes were identified. An in-depth analysis of the data revealed that a large number of genes were associated with drought stress, including transcription factors and genes involved in photosynthesis-antenna proteins, carbon metabolism and the citrate cycle. The results of this study provide insights into the diverse mechanisms that underlie the successful establishment of drought resistance in the peanut, thereby facilitating the identification of important genes in the peanut related to drought management. Transcriptome analysis based on RNA-Seq is a powerful approach for gene discovery and molecular marker development for this species.

Genome-wide analysis of expansin superfamily in wild Arachis discloses a stress-responsive expansin-like B gene

Expansins are plant cell wall-loosening proteins involved in adaptive responses to environmental stimuli and various developmental processes. The first genome-wide analysis of the expansin superfamily in the Arachis genus identified 40 members in A. duranensis and 44 in A. ipaënsis, the wild progenitors of cultivated peanut (A. hypogaea). These expansins were further characterized regarding their subfamily classification, distribution along the genomes, duplication events, molecular structure, and phylogeny. A RNA-seq expression analysis in different Arachis species showed that the majority of these expansins are modulated in response to diverse stresses such as water deficit, root-knot nematode (RKN) infection, and UV exposure, with an expansin-like B gene (AraEXLB8) displaying a highly distinct stress-responsive expression profile. Further analysis of the AraEXLB8 coding sequences showed high conservation across the Arachis genotypes, with eight haplotypes identified. The modulation of AraEXLB8 expression in response to the aforementioned stresses was confirmed by qRT-PCR analysis in distinct Arachis genotypes, whilst in situ hybridization revealed transcripts in different root tissues according to the stress imposed. The overexpression of AraEXLB8 in soybean (Glycine max) composite plants remarkably decreased the number of galls in transformed hairy roots inoculated with RKN. This study improves the current understanding of the molecular evolution, divergence, and gene expression of expansins in Arachis, and provides molecular and functional insights into the role of expansin-like B, the less-studied plant expansin subfamily.

Profiling of BABA-induced differentially expressed genes of Zea mays using suppression subtractive hybridization

This study aims to identify differentially expressed transcripts in BABA-primed maize leaves using suppression subtractive hybridization (SSH) strategy. Findings shed new light on the BABA potentiated defense mechanisms in plants.

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.

Transcriptional profiling in pearl millet (Pennisetum glaucum L.R. Br.) for identification of differentially expressed drought responsive genes

Pearl millet (Pennisetum glaucum) is an important cereal of traditional farming systems that has the natural ability to withstand various abiotic stresses. The present study aims at the identification and validation of major differentially expressed genes in response to drought stress in P. glaucum by Suppression Subtractive Hybridization (SSH) analysis. Twenty-two days old seedlings of P. glaucum cultivar PPMI741 were subjected to drought stress by treatment of 30 % Polyethylene glycol for different time periods 30 min (T1), 2 h (T2), 4 h (T3), 8 h (T4), 16 h (T5), 24 h (T6) and 48 h (T7) respectively, monitored by examining the RWC of seedlings. Total RNA was isolated to construct drought responsive subtractive cDNA library through SSH, sequenced to identify the differentially expressed genes in response to drought stress and validated by qRT-PCR.745 ESTs were assembled into a collection of 299 unigenes having 52 contigs and 247 singletons. All 745 ESTs were submitted to ENA-EMBL databases (Accession no. HG516611- HG517355). After analysis, 10 differentially expressed genes were validated namely Abscisic stress ripening protein, Ascorbate peroxidase, Inosine-5'-monophosphate dehydrogenase, Putative beta-1, 3-glucanase, Glyoxalase, Rab7, Aspartic proteinase Oryzasin, DnaJ-like protein and Calmodulin-like protein by qRT-PCR. The identified ESTs reveal a major portion of the stress responsive transcriptome that may prove to be a vent to unravel molecular basis underlying tolerance of pearl millet (Pennisetum glaucum) to drought stress. These genes could be utilized for transgenic breeding or transferred to crop plants through marker assisted selection for the development of better drought resistant cultivars having enhanced adaptability to survive harsh environmental conditions.