An SAPK10-RISBZ1-ABT axis promotes endosperm-to-embryo ABA transport to enhance pre-harvest sprouting tolerance in rice.

Weak dormancy can lead to pre-harvest sprouting (PHS) of crops, which seriously affects grain yield and quality. During seed development, endosperm-derived ABA is transported into embryo to prevent PHS. However, the underlying molecular mechanism remains unclear. Here, we report the map-based cloning of PHS7, encoding an ABA-inducible bZIP transcription factor RISBZ1, positively regulates PHS tolerance. Through an ‶SAPK10- RISBZ1-ABT″ module, the SnRK2 family kinase SAPK10 senses the ABA signal to phosphorylate RISBZ1 at Ser190, thus enhance its transactivation activity on an ABC transporter gene ABT. Serves as an ABA efflux transporter located in the embryo-endosperm interface, ABT mediates the endosperm-to-embryo transport of ABA to elevate the ABA level in embryo, which promotes embryo dormancy and suppresses PHS. The A339I variation in the CDS of RISBZ1 confers the indica type RISBZ1Hap1 higher transactivation activity on ABT than the japonica type RISBZ1Hap2, thereby contributing to the difference in PHS resistance between indica and japonica subspecies. Combined analysis of the RISBZ1-ABT genotypes revealed that the RISBZ1Hap1-ABTHap1 module confers the lowest germination rate and optimal PHS resistance performance, suggesting that the RISBZ1-ABT module should be considered in improving PHS resistance. Using either a transgenic approach or marker-assisted selection, we demonstrated that RISBZ1 could effectively enhance PHS tolerance in cultivars and derived hybrids. This work shed new light on PHS regulation by the communication of ABA within a seed, and provided excellent genetic resources for PHS genetic improvement.