P-397 - An apoplastic class II glycine-rich protein functions as an endogenous elicitor of systemic acquired resistance in plants

Systemic acquired resistance (SAR) is an important fitness-optimizing strategy in plants. LsGRP1, an apoplastic class II glycine-rich protein (GRP) abundantly accumulated during the induced disease resistance of Lilium, positively regulates both plant growth and defense against diverse pathogens. In this study, locally endogenous expression and exogenous application of LsGRP1 were found to systemically enable disease resistance enhancement and defense priming in LsGRP1-originated Lilium and dicot model Arabidopsis. By using SAR long-distance signaling-related mutants of Arabidopsis, LsGRP1 was demonstrated to confer systemic protection via salicylic acid- and L-lysine metabolite N-hydroxypipecolic acid-involving pathways rather than that of the other DIR1-dependent molecules. The transcriptional regulation of LsGRP1-elicited SAR was then characterized using quantitative RT-PCR analysis in Arabidopsis. Besides, the immune activation-enhancing domain of LsGRP1 was validated to enable SAR in Arabidopsis and Lilium. Whether the apoplastic receptor essential for sensing this domain participating in SAR elicitation requires further investigation. To summarize, LsGRP1 functions as an endogenous defense-priming factor to initiate SAR, offering insight into the connection between apoplastic monitoring and long-distance signaling during SAR establishment.