The OsARF12 - bZIP23 module links auxin signaling to ABA-associated regulatory pathways to improve seed vigor in rice

Abstract

Seed vigor in plants can refer to the overall capacity of seeds to germinate and affect seedling morphogenesis, which is a key agronomic trait indicator of seed quality. However, the underlying gene network mechanism is unclear. Here, we report an important role played by the coordination of abscisic acid (ABA) and auxin signaling in controlling rice seed vigor. The core ABA signaling component STRESS ACTIVATED PROTEIN KINASE 1 (SAPK1) is a positive modulator of the trait, which physically interacts with and phosphorylates the transcription factor bZIP23, and importantly, the phosphorylated bZIP23 exhibits stronger transactivation activity and improved seed vigor. Furthermore, OsARF12 directly binds to the promoter of bZIP23 and activates its expression. Quite coincidentally, our genetic and molecular experimental results verify that the OsTIR1-OsIAA10-OsARF12-centered auxin signaling is required for seed vigor control. Overall, our findings uncover the auxin signaling and SAPK1-bZIP23-mediated ABA signaling pathways, converging at the OsARF12-bZIP23 axis, to endow seeds with improved vigor in rice.