Integrative Regulation of Drought Escape through ABA-Dependent and -Independent Pathways in Rice

Many plants have evolved a drought escape (DE) mechanism to shorten their life cycle when facing water deficit conditions. While drought tolerance has been intensively investigated, the genetic and molecular mechanisms of DE remain elusive. In this study, we found that low water-deficit treatment (LWT) at the early stage of rice development can trigger early flowering and reduced tiller numbers. LWT induced the accumulation of abscisic acid (ABA), which in turn has feed-back effects on light perception and circadian clock by synchronously regulating many flowering-related genes to promote early flowering. Moreover, some of light receptors, circadian components, and flowering-related genes including OsTOC1, Ghd7, and PhyB were found to be involved in LWT in an ABA-dependent manner, whereas some of the other flowering-related genes including OsG1, OsELF3, OsPRR37, and OsMADS50 were involved in the regulation of DE independent of ABA. In addition, we found that strigolactones and OsTB1 are involved in the tillering inhibition under LWT, which is independent of the flowering pathway in rice. Taken together, our findings provide compelling evidence that DE in rice is coordinately regulated by multiple pathways during the reproduction (flowering) switch.