Noncanonical Function of a Small-Molecular Virulence Factor Coronatine against Plant Immunity: An Raman Imaging Approach.

Coronatine (), a small-molecular virulence factor produced by plant-pathogenic bacteria, promotes bacterial infection by inducing the opening of stomatal pores, the major route of bacterial entry into the plant, via the jasmonate-mediated COI1-JAZ signaling pathway. However, this pathway is also important for multiple plant functions, including defense against wounding by herbivorous insects. Thus, suppression of the COI1-JAZ signaling pathway to block bacterial infection would concomitantly impair plant defense against herbivorous wounding. Here, we report additional, COI1-JAZ-independent, action of in guard cells. First, we found that a stereoisomer of regulates the movement of guard cells without affecting COI1-JAZ signaling. Second, we found using alkyne-tagged Raman imaging (ATRI) that is localized to the endoplasmic reticulum (ER) of living guard cells of . The use of mutant lacking chloroplast formation was pivotal to circumvent the issue of autofluorescence during ATRI. These findings indicate that has an ER-related action on stomata that bypasses the COI1-JAZ signaling module. It may be possible to suppress the action of on stomata without impairing plant defense responses against herbivores.