Abscisic acid (ABA) is associated with multiple developmental processes in higher plants, especially to respond to abiotic stresses. ABA synthesis is triggered by various environmental factors and ABA sensing promotes leaf senescence or stress tolerance. Here, we demonstrate a rice MYB transcription factor RADIALIS-LIKE3 (OsRL3) which promotes dark-induced senescence (DIS) and salt stress response. The gene expression is slightly induced under DIS and some osmotic stress conditions, highly expressed under salt stress. The T-DNA insertion osrl3 knockout mutant delayed leaf senescence in the dark with a significant retention of chlorophylls and photosynthetic capacity. Furthermore, in high salinity conditions, osrl3 mutation increased stress response with reduced expression of proline biosynthetic genes OsP5CS1 and OsP5CS2 in the leaves. In an exogenous ABA treatment, OsRL3 expression increased in the WT leaves and osrl3 mutant exhibit a stay-green phenotype. Under both dark and salt stress treatments, ABA signaling-associated genes were down-regulated in osrl3. Yeast one-hybrid assay revealed that OsRL3 directly targets the promoters of OsNAP and OsRAB16D that accelerate leaf senescence and abiotic stress response. Taking together, we conclude that OsRL3 functions as a transcriptional activator for the genes involved in ABA signaling which promotes leaf senescence and abiotic stress response in rice.
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