AtERF15 is a positive regulator of ABA response

The Arabidopsis AP2/ERF family transcription factor AtERF15 is nuclear-localized and positively regulates ABA and stress responses. Abscisic acid (ABA) is a major plant hormone that controls the expression of hundreds genes involved in various aspects of plant growth and development, such as seed development, germination, seedling growth and abiotic stress response. Several cis-elements mediating the ABA-regulated gene expression have been reported, and one of the regulatory elements is Coupling Element 1 (CE1). We previously isolated a group of AP2/ERF family proteins that bind CE1, but their functions are mostly unknown. In this study, we demonstrate that one of the CE1 binding factors (CEBFs), AtERF15, is involved in ABA response. To investigate the AtERF15 function, we generated its overexpression (OX) lines by expressing the AtERF15 coding region under the control of CaMV 35S promoter and analyzed their phenotypes. We found that the AtERF15 OX lines were hypersensitive to ABA at the germination stage. The ABA hypersensitivity was also observed in our root elongation assay of seedlings. Furthermore, the transgenic lines were hypersensitive to high salinity and high osmolarity at the seedling establishment stage, and the transgenic seedlings were drought-tolerant. We also determined the tissue-specific expression pattern and the subcellular localization of AtERF15. Our results indicate that it is highly expressed in roots and embryos and nuclear-localized. Collectively, our data suggest that AtERF15 is a positive regulator of ABA response.