Transcription Factor <i>MdWRKY32</i> Participates in Starch–Sugar Metabolism by Binding to the <i>MdBam5</i> Promoter in Apples During Postharvest Storage

Abstract

Starch degradation with fruit ripening is closely related to the aging process and flavor formation in apples. In this study, ethylene, 1-methylcyclopropene (1-MCP), and apples treated at different temperatures were used to determine the key genes of starch-sugar metabolism during storage. Compared with 4 °C storage, 20 °C storage promoted starch degradation and sugar accumulation in apples. In addition, ethylene treatment promoted starch degradation and sugar accumulation in apples, while 1-MCP treatment showed the opposite effects. The expression of <i>MdBams</i> indicated the crucial role of <i>MdBam5</i> in starch-sugar conversion. Transient overexpression of <i>MdBam5</i> significantly reduced the starch content in apples. Furthermore, <i>MdWRKY32</i> directly combined the <i>MdBam5</i> promoter and activated the <i>MdBam5</i> expression, which may promote the starch degradation in apples. Therefore, it was concluded that <i>MdWRKY32</i> may be involved in the regulation of starch-sugar metabolism in postharvest apples by activating the <i>MdBam5</i> expression.