A Rice R2R3-Type MYB Transcription Factor OsFLP Positively Regulates Drought Stress Response via OsNAC

Abiotic stresses adversely affect plant growth and the yield of crops worldwide. R2R3-MYB transcriptional factors have been found to be vital for plants to confer stress response. In Arabidopsis, FOUR LIPS (FLP, MYB124) and its paralogous MYB88 function redundantly regulated the symmetric division of guard mother cells (GMCs) and abiotic stress response. Here, OsFLP was identified as an R2R3-MYB transcriptional activator and localized in the nucleus. OsFLP was transiently induced by drought, salt stress and abscisic acid (ABA). Overexpression of OsFLP showed enhanced tolerance to drought and salt stresses. The stomatal density in OsFLP-OE plants was not changed, whereas the stomatal closure was sensitive to ABA treatment compared to wild-type plants. In contrast, OsFLP-RNAi plants had abnormal stomata and were sensitive to drought. Moreover, the transcripts of stomatal closure-related genes DST and peroxidase 24 precursor, which are identified as downstream of OsNAC1, were inhibited in OsFLP-RNAi plants. The yeast-one-hybrid assay indicated that OsFLP can specifically bind and positively regulate OsNAC1 and OsNAC6. Meanwhile, stress response genes, such as OsLEA3 and OsDREB2A, were up-regulated in OsFLP-OE plants. These findings suggested that OsFLP positively participates in drought stress, mainly through regulating regulators' transcripts of OsNAC1 and OsNAC6.