PAD4 was induced in response to aphid feeding, but was significantly reduced in response to clubroot infection (Figure S6B), Thus, BIK1 acts as a negative regulator of the defense response against the infection of P. brassicae, and the mechanism may be different from that of the resistance of BIK1 against biotrophic bacterial pathogens and phloem sap-feeding aphids. The gene discussed is PADI4; the disease is infection.