Functional Genomics and Transcriptomics on Abiotic Stresses in Rice

To better understand abiotic stress tolerant mechanism and to further improve rice varieties in their tolerance, we have carried out studies on functional genomics and transcriptomics. We have developed an efficient two-element maize Activator/Dissociation (Ac/Ds) gene trapped system and generated around 20,000 Ds insertion rice lines. We subjected these lines to drought, high salinity and cold stress screens and evaluated these lines and their tagged genes. Our data show that random Ds insertions into the rice genome have led to various variations in response to these stresses. Although hundreds of genes might contribute to abiotic stress tolerance, knock-out of single gene could significantly increase or decrease rice tolerance. We have also genome-widely identified genes with differential expression under drought and high salinity stresses between tolerant and sensitive rice lines. These genes encode various proteins functioning as transcription factor, kinase, and phosphatase as well as in detoxification, iron homeostasis, and hormone biosynthesis and so on. We have over-expressed two of these genes independently in the rice genome. One of them is OEX2 encoding an ethylene-responsive transcription factor and another one is OEX3 encoding a homeobox associated leucine zipper. Transgenic plants showed statistically higher biomass yield, stronger roots and taller plant height when compared with the wild type plants under high salinity or drought stress. Further investigation showed that these two genes played roles in ABA-dependent stress signaling pathway and after overexpression of OEX3, some stress-related genes were up- or down-regulated, which might also contribute to the improved tolerance to these stresses.