<i>BrCCX1</i> Negatively Regulates Calcium‐Mediated Clubroot Resistance in Chinese Cabbage

Chinese cabbage (Brassica rapa L. ssp. pekinensis) is severely threatened by clubroot disease caused by Plasmodiophora brassicae. In this study, the expression of Cation/Ca²⁺ exchanger 1 in B. rapa, BrCCX1, was found to be significantly induced by P. brassicae in Chinese cabbage. BrCCX1 was verified as a negative regulator of clubroot resistance in A. thaliana ccx1 mutant, and BrCCX1-silenced/-overexpressed Chinese cabbage. Exogenous calcium induced clubroot resistance in Chinese cabbage, and silencing of BrCCX1 enhanced this resistance. These results suggested that the negative regulation of BrCCX1 to clubroot resistance is related to calcium signal. BrMYB106 was identified as a direct binder and negative regulator of the BrCCX1 promoter through yeast one-hybrid (Y1H), Dual-luciferase (LUC) and β-glucuronidase (GUS) activity assay. BrMYB106 was verified as a positive regulator of clubroot resistance by virus-induced gene silencing (VIGS) and transiently overexpression. In summary, BrCCX1 is a negative regulator of calcium-mediated clubroot resistance modulated by BrMYB106. The study provided the basis for utilising the BrCCX1 gene to develop clubroot-resistant cultivars in Chinese cabbage.