AtEAU1 and AtEAU2, Two EAR Motif-Containing ABA Up-Regulated Novel Transcription Repressors Regulate ABA Response in Arabidopsis

EAR (Ethylene-responsive element binding factor-associated Amphiphilic Repression) motif-containing transcription repressors have been shown to regulate plant growth and development, and plant responses to plant hormones and environmental stresses including biotic and abiotic stresses. However, the functions of most EAR-motif-containing proteins remain largely uncharacterized. The plant hormone abscisic acid (ABA) also plays important roles in regulating plant responses to abiotic stresses via activation/repression of ABA-responsive genes. We report here the identification and functional characterization of two ABA-responsive EAR motif-containing protein genes, AtEAU1 (Arabidopsis thaliana EAR motif-containing ABA Up-regulated 1) and AtEAU2. Quantitative RT-PCR results show that the expressions of AtEAU1 and AtEAU2 were increased by ABA treatment, and were decreased in the ABA biosynthesis mutant aba1-5. Assays in transfected Arabidopsis protoplasts show that both AtEAU1 and AtEAU2 were specifically localized in the nucleus, and when recruited to the promoter region of the reporter gene by a fused DNA binding domain, repressed reporter gene expression. By using T-DNA insertion mutants and a gene-edited transgene-free mutant generated by CRISPR/Cas9 gene editing, we performed ABA sensitivity assays, and found that ABA sensitivity in the both ateau1 and ateau2 single mutants was increased in seedling greening assays. ABA sensitivity in the ateau1 ateau2 double mutants was also increased, but was largely similar to the ateau1 single mutants. On the other hand, all the mutants showed a wild type response to ABA in root elongation assays. Quantitative RT-PCR results show that the expression level of PYL4, an ABA receptor gene was increased, whereas that of ABI2, a PP2C gene was decreased in the ateau1 and ateau1 single, and the ateau1 ateau2 double mutants. In summary, our results suggest that AtEAU1 and AtEAU2 are ABA-response genes, and AtEAU1 and AtEAU2 are novel EAR motif-containing transcription repressors that negatively regulate ABA responses in Arabidopsis, likely by regulating the expression of some ABA signaling key regulator genes.