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HrpNEa 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 HrPNEa 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 HI-pNEa significantly decreased seventies 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 HrPNE. on the root attachment and quorum-sensing signals accompanied the induced expression of several defense response genes. These results suggest that HrPNEa induces Chinese cabbage resistance to bacterial soft rot by inhibiting the bacterial attachment to root surfaces. [ABSTRACT FROM AUTHOR]

Lumazine synthase (LS) catalyzes the penultimate reaction in the multistep riboflavin biosynthesis pathway, which is involved in plant defenses. Plant defenses are often subject to synergistic effects of jasmonic acid and ethylene whereas LS is a regulator of jasmonic acid signal transduction. However, little is known about whether the enzyme contributes to defense responses. To study the role of LS in plant pathogen defenses, we generated transgenic tobacco expressing the rice (Oryza sativa) LS gene, OsLS. OsLS was cloned and found to have strong identity with its homologues in higher plants and less homology to microbial orthologues. The OsLS protein localized to chloroplasts in three OsLS-expressing transgenic tobacco (LSETT) lines characterized as enhanced in growth and defend. Compared with control plants, LSETT had higher content of both riboflavin and the cofactors flavin mononucleotide and flavin adenine dinucleotide. In LSETT, jasmonic acid and ethylene were elevated, the expression of defense-related genes was induced, levels of resistance to pathogens were enhanced, and resistance was effective to viral, bacterial, and oomycete pathogens. Extents of OsLS expression correlated with increases in flavin, jasmonic acid, and ethylene content, and correlated with increases in resistance levels, suggesting a role for OsLS in defense responses. [ABSTRACT FROM AUTHOR]