Drought Resistance and Molecular Responses in Soybean.

Drought response in soybean was studied in Glycine max (Var: V71-370) and recombinant inbred lines (RILs) between this variety and Glycine soja (PI407162). In a preliminary segregation analysis of drought resistance at vegetative stage, a sample of three RILs were assayed for the rate of biomass reduction (RBR %) and water use efficiency (WUE) at soil moisture content of 40% of the controls for 14 days. Results indicated that RIL 32 had a lower RBR% and higher WUE, suggesting its resistance to drought. To analyze genome-level responses to drought, Affymetrix microarrays were used to profile gene expression changes in the leaf tissue of V71-370 at 40% soil moisture content. Drought-stressed plants reached 81% relative water content (RWC %), and photosynthesis parameters (Fv/Fm) and PSII were reduced but not significantly different from well-watered control plants. Transcriptome data analysis indicated that 374 genes were differentially regulated; of these, 155 were induced, while 219 genes were repressed by drought.  Among the induced genes, several that are known to be induced by osmotic stress and drought included RD22, zeaxanthin epoxide, and SNK 3.11. Gene ontology analysis revealed that differentially expressed genes were involved in diverse biological processes, such as response to osmotic stress, hormone signaling, monocarboxylic acid metabolism, protein and phenylpropanoid biosynthesis, and cell wall organization. Promoter regions of genes differentially expressed also indicated the presence of cis-regulatory elements, such as the ABA responsive element (ABRE), MYB, and MYC responsive elements known to be associated with water stress response.