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

Peanut (Arachis hypogaeaL.) is an important le-gume cultivated mostly in drought-prone areas where its pro-ductivity can be limited by water scarcity. The development of more drought-tolerant varieties is, therefore, a priority for pea-nut 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 analysi 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 sig-nificant 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 recov-ery 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 pea-nut. These together constitute important tools for the peanut breeding program and also contribute to a better comprehen-sion of gene modulation in response to water deficit and rehydration.