The transcription factor WRKY22 modulates ethylene biosynthesis and root development through transactivating the transcription of ACS5 and ACO5 in Arabidopsis

Abstract The WRKY transcription factor (TF) genes form a large family in higher plants, with 72 members in Arabidopsis ( Arabidopsis thaliana ). The gaseous phytohormone ethylene (ET) regulates multiple physiological processes in plants. It is known that 1‐aminocyclopropane‐1‐carboxylic acid (ACC) synthases (ACSs, EC 4.4.1.14) limit the enzymatic reaction rate of ethylene synthesis. However, whether WRKY TFs regulate the expression of ACSs and/or ACC oxidases ( ACOs , EC 1.14.17.4) remains largely elusive. Here, we demonstrated that Arabidopsis WRKY22 positively regulated the expression of a few ACS and ACO genes, thus promoting ethylene production. Inducible overexpression of WRKY22 caused shorter hypocotyls without ACC treatment. A qRT‐PCR screening demonstrated that overexpression of WRKY22 activates the expression of several ACS and ACO genes. The promoter regions of ACS5 , ACS11, and ACO5 were also activated by WRKY22, which was revealed by a dual luciferase reporter assay. A follow‐up chromatin immunoprecipitation coupled with quantitative PCR (ChIP‐qPCR) and electrophoretic mobility shift assay (EMSA) showed that the promoter regions of ACS5 and ACO5 could be bound by WRKY22 directly. Moreover, wrky22 mutants had longer primary roots and more lateral roots than wild type, while WRKY22 ‐overexpressing lines showed the opposite phenotype. In conclusion, this study revealed that WRKY22 acts as a novel TF activating, at least, the expression of ACS5 and ACO5 to increase ethylene synthesis and modulate root development.