Protein elicitor PemG1 from Magnaporthe grisea induces systemic acquired resistance (SAR) in plants

Elicitors can stimulate defense responses in plants and have become a popular strategy in plant disease control. Previously, we isolated a novel protein elicitor, PemG1, from Magnaporthe grisea. In the present study, PemG1 protein expressed in and purified from Escherichia coli improved resistance of rice and Arabidopsis to bacterial infection, induced transient expression of pathogenesis-related (PR) genes, and increased accumulation of hydrogen peroxide in rice. The effects of PemG1 on disease resistance and PR gene expression were mobilized systemically throughout the rice plant and persisted for more than 28 days. PemG1-induced accumulation of OsPR-1a in rice was prevented by the calcium channel blockers LaCl₃, BAPTA, EGTA, W7, and TFP. Arabidopsis mutants that are insensitive to jasmonic acid (JA) and ethylene showed increased resistance to bacterial infection after PemG1 treatment but PemG1 did not affect resistance of mutants with an impaired salicylic acid (SA) transduction pathway. In rice, PemG1 induced overexpressions of the SA signal-related genes (OsEDS1, OsPAL1, and OsNH1) but not the JA pathway-related genes (OsLOX2 and OsAOS2). Our findings reveal that PemG1 protein can function as an activator of plant disease resistance, and the PemG1-mediated systemic acquired resistance is modulated by SA- and Ca(2+)-related signaling pathways.