RNA-Seq analysis of rice varieties Nagina22 and IR64 in adult tissues of Flag leaf, inflorescence and root under control and field drought conditions.. Variety-specific transcript accumulation during reproductive stage drought stress in rice

The divergence of natural stress tolerance mechanisms is an intriguing phenomenon. To study it in rice, a comparative transcriptome analysis was carried out in heading stage tissue of flag leaf, panicles and roots of Nagina 22, a drought-tolerant and IR64, a drought-sensitive variety, subjected to field drought. Interestingly, N22 showed almost double the number of differentially expressed genes than IR64. Many DEGs colocalized within drought-related QTLs responsible for grain yield and drought tolerance and also associated with drought tolerance and critical drought-related plant traits such as leaf rolling, trehalose content, sucrose and cellulose content. Besides, co-expression analysis of the DEGs revealed several HUB genes known to actively regulate drought stress response. Strikingly, 1366 DEGs, including 21 HUB genes, showed a distinct opposite regulation in the two rice varieties under similar drought conditions. Annotation of these variety-specific DEGs revealed that they are distributed in various biological pathways. Furthermore, 103 VS-DEGs were found to physically interact with over 1300 genes, including 32 that physically interact with other VS-DEGs as well. The promoter region of these genes have sequence variations among the two rice varieties, which might be in part responsible for their unique expression pattern.