Overexpression of OsERF48 causes regulation of OsCML16, a calmodulin‐like protein gene that enhances root growth and drought tolerance

The AP2/ERF family is a plant‐specific transcription factor family whose members have been associated with various developmental processes and stress tolerance. Here, we functionally characterized the drought‐inducible OsERF48, a group Ib member of the rice ERF family with four conserved motifs, CMI‐1, ‐2, ‐3 and ‐4. A transactivation assay in yeast revealed that the C‐terminal CMI‐1 motif was essential for OsERF48 transcriptional activity. When OsERF48 was overexpressed in an either a root‐specific (ROX(O) (s) (ERF) (48)) or whole‐body (OX(O) (s) (ERF) (48)) manner, transgenic plants showed a longer and denser root phenotype compared to the nontransgenic (NT) controls. When plants were grown on a 40% polyethylene glycol‐infused medium under in vitro drought conditions, ROX(O) (s) (ERF) (48) plants showed a more vigorous root growth than OX(O) (s) (ERF) (48) and NT plants. In addition, the ROX(O) (s) (ERF) (48) plants exhibited higher grain yield than OX(O) (s) (ERF) (48) and NT plants under field‐drought conditions. We constructed a putative OsERF48 regulatory network by cross‐referencing ROX(O) (s) (ERF) (48) root‐specific RNA‐seq data with a co‐expression network database, from which we inferred the involvement of 20 drought‐related genes in OsERF48‐mediated responses. These included genes annotated as being involved in stress signalling, carbohydrate metabolism, cell‐wall proteins and drought responses. They included, OsCML16, a key gene in calcium signalling during abiotic stress, which was shown to be a direct target of OsERF48 by chromatin immunoprecipitation‐qPCR analysis and a transient protoplast expression assay. Our results demonstrated that OsERF48 regulates OsCML16, a calmodulin‐like protein gene that enhances root growth and drought tolerance.