ABI5 modulates seed germination via feedback regulation of the expression of the PYR/PYL/RCAR ABA receptor genes

As abscisic acid (ABA) receptors, PYR1/PYL/RCAR (PYLs) play important roles in ABA-mediated seed germination, but the regulation of PYLs in this process, especially at the transcriptional level, remains unclear. In this study, we found that expression of 11 of 14PYLs changes significantly during seed germination and is affected by exogenous ABA. Two PYLs, PYL11 and PYL12, both of which are expressed specifically in mature seeds, positively modulate ABA-mediated seed germination. However, ABI5 was found to modulate the PYL11- and PYL12-mediated ABA response. In theabi5-7mutant, ABA hypersensitivity caused byPYL11andPYL12overexpression was totally or partially blocked. By contrast, ABI5 regulates the expression ofPYL11andPYL12by directly binding to their promoters. Moreover, the expression of eight otherPYLs is also affected during the germination ofabi5mutants. Promoter analysis revealed that an ABI5-binding region is present next to the TATA box or initiator box. Together, our data demonstrate the role of PYL11 and PYL12 in seed germination. In addition, the identification ofPYLs as targets of ABI5 reveals a role of ABI5 in the feedback regulation of ABA-mediated seed germination.