OsbZIP09, a Unique OsbZIP Transcription Factor of Rice, Promotes Rather Than Suppresses Seed Germination by Attenuating Abscisic Acid Pathway

Abstract

We successfully identified a novel and unique OsbZIP transcription factor, OsbZIP09, whose mutants exhibited longer seeds and less severe pre-harvest sprouting than the wild type, but shared similar germination rate as the wild type under normal germination conditions. The expression of OsbZIP09 was induced by abscisic acid (ABA) and declined as the germination process. As a nucleus-localized transcription factor, the conserved binding motif of OsbZIP09 was identified via DNA affinity purification sequencing technique. Further evidences indicated that OsbZIP09 directly enhanced the expression of ABA catabolism gene ABA8ox1, thus reducing ABA accumulation. In addition, OsbZIP09 also directly bound to the promoter of LEA3 gene to inhibit its expression, thus further alleviating the suppressive effect of ABA on seed germination. These results demonstrated that OsbZIP09 likely functions as a brake of the ABA pathway to attenuate the inhibitory effect of ABA on rice seed germination via dual strategies.