MdWRKY11 improves copper tolerance by directly promoting the expression of the copper transporter gene MdHMA5

Abstract

Overuse of fungicides and fertilizers has resulted in copper (Cu) contamination of soils and toxic levels of Cu in apple fruits. To breed Cu-resistant apple (<i>Malus domestica</i>) cultivars, the underlying molecular mechanisms and key genes involved in Cu resistance must be identified. Here, we show that MdWRKY11 increases Cu tolerance by directly promoting the transcription of <i>MdHMA5</i>. MdHMA5 is a Cu transporter that may function in the storage of excess Cu in root cell walls and stems for Cu tolerance in apple. The transcription factor MdWRKY11 is highly induced by excess Cu. <i>MdWRKY11</i> overexpression in transgenic apple enhanced Cu tolerance and decreased Cu accumulation. Apple calli transformed with an <i>MdWRKY11</i>-RNAi construct exhibited the opposite phenotype. Both an in vivo chromatin immunoprecipitation assay and an in vitro electrophoretic mobility shift assay indicated that MdWRKY11 binds to the promoter of <i>MdHMA5</i>. Furthermore, MdWRKY11 promoted <i>MdHMA5</i> expression in transgenic apple plants, as revealed by quantitative PCR. Moreover, inhibition of <i>MdWRKY11</i> expression by RNA interference led to a significant decrease in <i>MdHMA5</i> transcription. Thus, MdWRKY11 directly regulates <i>MdHMA5</i> transcription. Our work resulted in the identification of a novel MdWRKY11-MdHMA5 pathway that mediates Cu resistance in apple.