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HrpN_Ea Induces Chinese Cabbage Resistance to Bacterial Soft Rot by Inhibiting the Bacterial Attachment to Root Surfaces

HrpN_Ea is a harpin protein produced by the bacterial plant pathogen Erwinia amylovora. When applied to aerial parts of plants, the protein induces systemic acquired resistance in a variety of plant species. Here, we report that treating Chinese cabbage roots with HrpN_Ea induces resistance of the plant to Pectobacterium carotovora subsp. carotovora, the pathogen that invades roots and causes bacterial soft rot in cruciferous plants. Treating Chinese cabbage roots with HrpN_Ea significantly decreased severities of soft rot symptoms on the plant. The root treatment decreased the number of P. carotovora subsp. carotovora cells attached to root surfaces and inhibited the ability of P. carotovora subsp. carotovora to produce quorum-sensing signals, which regulate pathogenicity in a bacterial population-dependent manner. The inhibitory effects of HrpN_Ea on the root attachment and quorum-sensing signals accompanied the induced expression of several defense response genes. These results suggest that HrpN_Ea induces Chinese cabbage resistance to bacterial soft rot by inhibiting the bacterial attachment to root surfaces.