Metal-responsive elements confer cadmium response in Arabidopsis

Molecular, biochemical, and genetic experiments demonstrate that metal-responsive elements (MREs), initially identified in animals, confer the cadmium transcriptional response in Arabidopsis, thus providing deep functional insights of MREs in plants. Cadmium (Cd) is highly toxic to all organisms including plants. Cd-responsive gene transcription is a fundamental aspect of the Cd response, in which Cd stress regulatory cis-acting elements are essential. However, little is known regarding such elements in plants. Metal-responsive elements (MREs, 5'-TGCRCNC-3', R: A or G, N: any base) are essential for transcriptional induction of Cd in animals. MREs are also contained in the promoters of some Cd-regulated plant genes, but whether MREs confer Cd responses in plants is poorly defined. Herein, we used a previously identified MRE of the tobacco feedback-insensitive anthranilate synthase α-2 chain gene as a representative MRE (named as MREa, 5'-TGCACAC-3') to explore the roles of MREs in the transcriptional response to Cd stress in Arabidopsis thaliana. First, we showed that MREa conferred Cd stress responsiveness on a minimal promoter in both concentration- and time-dependent manners, whereas the mutated MREa did not. Second, MREa specifically bound nuclear extracts, displaying a biochemical characteristic of cis-acting elements. We screened and identified four MREa-binding transcription factors, including ethylene response factor 13 (AtERF13). At last, MREa could mediate AtERF13 to activate the β-glucuronidase (GUS) reporter expression. Overall, these molecular, biochemical, and genetic data suggest that MREa is instrumental in the Cd response in Arabidopsis, thus providing deep functional insights of MREs in plants.