P-091 - The PRR LORE is highly expressed at specific microbial colonization and entry sites

To sense and control microbial colonization, plants express a diverse set of pattern-recognition receptors (PRRs) at the cell surface that activate pattern-triggered immunity (PTI) upon sensing of microbe-associated molecular patterns (MAMPs). To date, the role of individual PRRs in forming a robust host immune barrier is not well understood, largely because the spatiotemporal expression patterns of most PRRs remain unknown. Using reporter plant lines expressing a nuclear-localized VENUS fluorophore, we mapped the promoter activity of the Arabidopsis thaliana PRR LIPOOLIGOSACCHARIDE-SPECIFIC REDUCED ELICITATION (LORE), that senses bacterial 3-hydroxylated fatty acids of medium-chain length (mc-3-HFAs), at cellular level. Our results show that LORE is strongly expressed at specific microbial colonization sites and potential entry ports for microbes into the apoplast, especially hydathodes. Although stomata are well-characterized gateways for bacterial pathogens, LORE is not expressed in stomatal guard cells. Our results suggest LORE to be involved rather in post-invasive immunity. In addition to the basal expression, LOREprom is strongly activated upon treatment with various MAMPs and damage. Furthermore, we show that LORE expression is age-dependent, with young leaves showing a stronger promoter activity than older leaves. Overall, our analyses suggest that immune receptor expression is highly cell type-specific and differentially regulated during a tissue's lifespan.