OsERF3 Plays A Role In Drought Response Through Negative Regulation Of Ethylene Biosynthesis In Rice

In plants, drought stress induces a series of physiological and biochemical responses, which include stomatal closure, repression of cell growth and photosynthesis, and activation of respiration. Plants also adapt to water deficit at both the cellular and molecular levels, for instance, by accumulating osmolytes and proteins specifically involved in stress responses. In plant organisms, many kinds of stress can induce enhanced ethylene emission. Accumulating researches reveal that increased level of ethylene will not only cause some symptoms of the stresses but also induce acclimation processes which aid plant survival. Under drought stress, high level ethylene emission will be induced, which further activates the expression of drought related genes, and thus enhances drought tolerance. During the process, a lot of regulators including activators, respressors and transcriptional complexes are evidenced to be associated with the regulation. As a result, plants evolved a mechanism to repress the excess expression of activator genes to avoid the strong response that may cause eternal harm to plant cells. EAR motif is one of the important repression motifs in plants, with a small length but powerful suppression. However, little is known about how the repressors are involved in the regulation of ethylene biosynthesis in rice.OsERF3, belonging to AP2/ERF superfamily, consists of 235 amino acids, having a conserved AP2 domain at 33-96 sites and an EAR-motif at the C terminal that has a conserved sequence: L/FDLNL/F(X)P. Previous research proved that OsERF3 shares 44% similarity with NtERF3 and binds to GCC-box in vivo, and represses the activity of AtERF5 in yeast. In the present report, our research reveals that OsERF3 can physically bind to GCC-box and DRE in the EMSA experiment and accumulates in the rice nuclear and cytoplasm in transient expression system, and OsERF3 can be induced by drought, salt, ACC and ABA treatment. In addition, OsERF3 expressed in all parts of the rice seedlings, with a higher expression level in root and sheath.To reveal the physiological function of OsERF3 and its EAR motif, we generated transgenic rice overexpressing full length (OE) and EAR mutation (mEAR) of OsERF3, respectively. Our analyses reveal that OE lines showed decreased drought tolerance compared to wild type, while ACC repressed the drought sensitivity in OE lines. On the contrary, mEAR seedlings displayed enhanced drought tolerance. Compared with wild type, OE lines showed higher ion leakage ratio, lower chlorophyll and proline contents under drought stress, and less ethylene emission, while mEAR rice produced more ethylene. Moreover, the expression of ethylene synthesis genes including ACO2, ACO3, ACS2 and ACS6 was decreased in OE lines, whereas the expression level of ACS2 was increased in mEAR rice. Our research reveals that OsERF3 negatively regulates ethylene biosynthesis, thereby decreasing drought tolerance.