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.
We have developed Stress Combinations and their Interactions in Plants Database (SCIPDb; http://www.nipgr.ac.in/scipdb.php), a compendium and interactive platform offering information on both morpho-physio-biochemical (phenome) and molecular (transcriptome) responses of plants to different combinations of stresses. To delineate the effects of various stress combinations/categories on yield in major agricultural crops, global phenome data from 939 studies was analyzed and results showed that yield was affected to the greatest extent under the abiotic-abiotic stress category, followed by the biotic-biotic and abiotic-biotic stress categories. In the abiotic-abiotic stress category, drought-heat, heat-salinity, and ozone-UV are the major stress combinations causing high yield loss in barley, wheat, soybean, and quinoa crops. In the abiotic-biotic stress category, the salinity-weed stress combination causes highest yield loss in rice crop. In the biotic-biotic stress category, the nematode-fungus combination was most detrimental, causing considerable yield losses in potato, groundnut, and sugar beet crops. Transcriptome datasets from 36 studies hosted in SCIPDb identified novel genes. Thus far, these genes have not been known to play a role in combined stress. Integretome analysis under combined drought-heat stress pinpointed carbohydrate, amino acid, and energy metabolism pathways as the crucial metabolic, proteomic, and transcriptional components in plant tolerance to combined stress. These examples illustrate the application of SCIPDb in identifying novel genes and pathways involved in combined stress tolerance. Further, we showed the application of this database in identifying novel candidate genes and pathways for combined drought and pathogen stress tolerance in Arabidopsis and chickpea. To our knowledge, SCIPDb is the only publicly available platform that provides extensive information and paves the way for advancing mechanistic understanding of plant responses to combined stresses.
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