miR2105 and the kinase OsSAPK10 co-regulate OsbZIP86 to mediate drought-induced ABA biosynthesis in rice.

Mediating induced abscisic acid (ABA) biosynthesis is important for enhancing plant stress tolerance. Here, we found that rice (Oryza sativa L.) osa-miR2105 (miR2105) and the Stress/ABA-activated protein kinase (OsSAPK10) coordinately regulate the rice basic region-leucine zipper transcription factor (bZIP TF; OsbZIP86) at the posttranscriptional and posttranslational levels to control drought-induced ABA biosynthesis via modulation of rice 9-cis-epoxycarotenoid dioxygenase (OsNCED3) expression. OsbZIP86 expression is regulated by miR2105-directed cleavage of the OsbZIP86 mRNA. OsbZIP86 encodes a nuclear TF that binds to the promoter of the ABA biosynthetic gene OsNCED3. OsSAPK10 can phosphorylate and activate OsbZIP86 to enhance the expression of OsNCED3. Under normal growth conditions, altered expression of miR2105 and OsbZIP86 displayed no substantial effect on rice growth. However, under drought conditions, miR2105 knockdown or OsbZIP86 overexpression transgenic rice plants showed higher ABA content, enhanced tolerance to drought, lower rates of water loss, and more stomatal closure of seedlings, compared with wild-type rice Zhonghua 11; in contrast, miR2105 overexpression, OsbZIP86 downregulation, and OsbZIP86 knockout plants displayed opposite phenotypes. Collectively, our results show that the "miR2105-(OsSAPK10)-OsbZIP86-OsNCED3" module regulates the drought-induced ABA biosynthesis without penalty on rice growth under normal conditions, suggesting candidates for improving drought tolerance in rice.