Mechanisms of far-red light-mediated dampening of defense against Botrytis cinerea in tomato leaves
Plants detect neighboring competitors through a decrease in the ratio between red and far-red light (R:FR). This decreased R:FR is perceived by phytochrome photoreceptors and triggers shade avoidance responses such as shoot elongation and upward leaf movement (hyponasty). In addition to promoting elongation growth, low R:FR perception enhances plant susceptibility to pathogens: the growth-defense trade-off. Although increased susceptibility in low R:FR has been studied for over a decade, the associated timing of molecular events is still unknown. Here, we studied the chronology of FR-induced susceptibility events in tomato plants pre-exposed to either white light (WL) or WL supplemented with FR light (WL+FR) prior to inoculation with the necrotrophic fungus Botrytis cinerea (B.c.). We monitored the leaf transcriptional changes over a 30-hr time course upon infection and followed up with functional studies to identify mechanisms. We found that FR-induced susceptibility in tomato is linked to a general dampening of B.c.-responsive gene expression, and a delay in both pathogen recognition and jasmonic acid-mediated defense gene expression. In addition, we found that the supplemental FR-induced ethylene emissions affect plant immune responses under WL+FR conditions. This study increases our understanding of the growth-immunity trade-off, while simultaneously providing leads to improve tomato resistance against pathogens in dense cropping systems. One-sentence summaryLow Red:Far-red ratio enhances tomato susceptibility towards the necrotrophic fungus Botrytis cinerea via delayed early pathogen detection and dampening of jasmonic acid-mediated defense activation.