EAR motif mutation of rice OsERF3 alters the regulation of ethylene biosynthesis and drought tolerance.

OsERF3 is a transcriptional repressor with an ethylene-responsive element-binding factor-associated amphiphilic repression (EAR) motif (F/LDLNxxP), which transcriptionally represses the ethylene emission and drought tolerance in rice. However, its molecular mechanism to explore repression function remains unknown. Here, we first revealed that the expression of OsERF3 was induced by drought, salt, ACC and ABA treatment. In addition, it showed a higher expression level in the root and sheath than that in the leaf. Then, we generated transgenic rice overexpressing full-length OsERF3 (OE) and its mutation of EAR motif with the A 680/C substitution (mEAR), respectively. The physiological analyses showed that mEAR lines showed better drought tolerance and more ethylene emission compared with those of OE lines and wild type plants. Consistent with our previous research, the expression of ethylene synthesis genes, including ACO2, ACS2, and ACS6 was down-regulated in OE lines. However, the repression of OsERF3 was eliminated in mEAR lines. Specifically, ACS2 was up-regulated in mEAR lines compared with that in OE lines and WT plants, suggesting that the Leu/Ala substitution within the EAR motif resulted in loss of repression of OsERF3. Thus, our data reveal that the EAR motif is required for OsERF3 to transcriptionally regulate the ethylene synthesis and drought tolerance in rice, providing new insight to the roles of ethylene-response factor proteins in regulating ethylene biosynthesis and stress response.