Overexpression of <i>Os<scp>ERF</scp>48</i> causes regulation of <i>Os<scp>CML</scp>16</i>, a calmodulin‐like protein gene that enhances root growth and drought tolerance

Abstract

Summary The AP 2/ 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 Os ERF 48 , 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 Os ERF 48 transcriptional activity. When Os ERF 48 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 Os ERF 48 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 Os ERF 48 ‐mediated responses. These included genes annotated as being involved in stress signalling, carbohydrate metabolism, cell‐wall proteins and drought responses. They included, Os CML 16 , a key gene in calcium signalling during abiotic stress, which was shown to be a direct target of Os ERF 48 by chromatin immunoprecipitation‐ qPCR analysis and a transient protoplast expression assay. Our results demonstrated that Os ERF 48 regulates Os CML 16 , a calmodulin‐like protein gene that enhances root growth and drought tolerance.