Stress adaptation in plants involves altered expression of many genes through complex signaling pathways. To achieve the optimum expression of downstream functional genes, we expressed AtbHLH17 (AtAIB) and AtWRKY28 TFs which are known to be upregulated under drought and oxidative stress, respectively in Arabidopsis. Multigene expression cassette with these two TFs and reporter gene GUS was developed using modified gateway cloning strategy. The GUS assay and expression analysis of transgenes in transgenic plants confirmed the integration of multigene cassette. The transgenic lines exhibited enhanced tolerance to NaCl, Mannitol and oxidative stress. Under mannitol stress condition significantly higher root growth was observed in transgenics. Growth under stress and recovery growth was substantially superior in transgenics exposed to gradual long term desiccation stress conditions. We demonstrate the expression of several downstream target genes under various stress conditions. A few genes having either WRKY or bHLH cis elements in their promoter regions showed higher transcript levels than wild type. However, the genes which did not have either of the motifs did not differ in their expression levels in stress conditions compared to wild type plants. Hence co-expressing two or more TFs may result in upregulation of many downstream target genes and substantially improve the stress tolerance of the plants.

Drought, salinity and extreme temperatures are the most common abiotic stresses, adversely affecting plant growth and productivity. Exposure of plants to stress activates stress signalling pathways that induce biochemical and physiological changes essential for stress acclimation. Stress tolerance is governed by multiple traits, and importance of a few traits in imparting tolerance has been demonstrated. Under drought, traits linked to water mining and water conservation, water use efficiency and cellular tolerance (CT) to desiccation are considered to be relevant. In this study, an attempt has been made to improve CT in drought hardy crop, peanut (Arachis hypogaea L., cv. TMV2) by co-expressing stress-responsive transcription factors (TFs), AtDREB2A, AtHB7 and AtABF3, associated with downstream gene expression. Transgenic plants simultaneously expressing these TFs showed increased tolerance to drought, salinity and oxidative stresses compared to wild type, with an increase in total plant biomass. The transgenic plants exhibited improved membrane and chlorophyll stability due to enhanced reactive oxygen species scavenging and osmotic adjustment by proline synthesis under stress. The improvement in stress tolerance in transgenic lines were associated with induced expression of various CT related genes like AhGlutaredoxin, AhAldehyde reductase, AhSerine threonine kinase like protein, AhRbx1, AhProline amino peptidase, AhHSP70, AhDIP and AhLea4. Taken together the results indicate that co-expression of stress responsive TFs can activate multiple CT pathways, and this strategy can be employed to improve abiotic stress tolerance in crop plants.

Improving drought tolerance through gene manipulation has been of importance for modern agriculture, which requires identification and validation of candidate genes. Prospecting candidate genes from drought adapted crop species is of immense significance. To identify candidate stress responsive genes from adapted crop, we carried out expression analysis of a few drought responsive ESTs from Arachis hypogaea L. (peanut). The expression patterns of nine AhDR (Arachis hypogea drought responsive) clones were analysed under drought. Quantitative reverse transcription PCR analysis revealed stress responsive nature of the selected genes. The clones AhDR 118 (putative cyclin T-like), AhDR185 (aldehyde reductase-like), AhDR193 (cholin kinase-like) and AhDR 76 (proline amino peptidase-like) showed more than five fold increase in expression. Highly upregulated genes analysed for expression pattern against salinity at seedling level indicated that these genes provide cross protection. This paper is the first report indicating the association of peanut genes cyclin T, proline amino peptidase and choline kinase to drought tolerance, and the possible roles of these genes are discussed.

Abiotic stresses limit crop growth and productivity worldwide. Cellular tolerance, an important abiotic stress adaptive trait, involves coordinated activities of multiple proteins linked to signalling cascades, transcriptional regulation and other diverse processes. Basal transcriptional machinery is considered to be critical for maintaining transcription under stressful conditions. From this context, discovery of novel basal transcription regulators from stress adapted crops like peanut would be useful for improving tolerance of sensitive plant types. In this study, we prospected a basal transcription factor, BTF3 from peanut (Arachis hypogaea L) and studied its relevance in stress acclimation by over expression in tobacco. AhBTF3 was induced under PEG-, NaCl-, and methyl viologen-induced stresses in peanut. The constitutive expression of AhBTF3 in tobacco increased plant growth under non stress condition. The transgenic plants exhibited superior phenotype compared to wild type under mannitol- and NaCl-induced stresses at seedling level. The enhanced cellular tolerance of transgenic plants was evidenced by higher cell membrane stability, reactive oxygen species (ROS) scavenging activity, seedling survival and vigour than wild type. The transgenic lines showed better in vitro regeneration capacity on growth media supplemented with NaCl than wild type. Superior phenotype of transgenic plants under osmotic and salinity stresses seems to be due to constitutive activation of genes of multiple pathways linked to growth and stress adaptation. The study demonstrated that AhBTF3 is a positive regulator of growth and stress acclimation and hence can be considered as a potential candidate gene for crop improvement towards stress adaptation.

Regulatory proteins such as protein kinases are known to play a crucial role in plant stress acclimation pathways. In this study, we report the identification and characterization of an abiotic stress responsive protein kinase called CBL Interacting Protein Kinase (EcCIPK31-like) from finger millet, a drought-tolerant crop. PCR-based approach was followed to clone 1350 bp coding region that encodes a 449 amino acid protein with a calculated molecular mass of 50.69 kDa. The conserved domain analysis revealed the presence of CIPK domain with 90% sequence similarity with fox tail millet SiCIPK31-like gene. We also report its upregulation under salinity, desiccation, oxidative and temperature stresses at seedling level in finger millet. Drought stress at wholeplant level significantly induced the expression of EcCIPK31-like, indicating that the gene is linked to drought signalling pathways. The stress-responsive nature of EcCIPK31-like to diverse stresses indicates that the gene could regulate multiple cellular tolerance traits and its further functional validation can highlight the relevance in abiotic stress acclimation in plants.