Effects of green light on the gene expression and virulence of the plant pathogen Pseudomonas cichorii JBC1.
Increasing evidence suggests that the interactions between plant and pathogen are influenced by light perception of both organisms. In our previous study, green light decreased disease severity in tomato plants in response to Pseudomonas cichorii JBC1 (PcJBC1) infection via induction of disease resistance-related genes. However, the influence of green light on gene expression and metabolism of PcJBC1 has not been explored. In this study, we cultured PcJBC1 in hrp-inducing minimal media (MM) under green light and dark condition, and analyzed the expression of genes, which are important in pathogenicity/virulence and epiphytic survival by real-time PCR (qPCR). Although no significant changes were observed in the expression of type 3 secretion system (T3SS)- and flagellar-related genes in response to green light, genes for the production of phytotoxic lipopeptides and siderophores were significantly reduced by green light. In addition, the phytotoxic lipopeptide and siderophore production in the culture supernatant was consistent with the results of gene expression. Furthermore, we compared the whole transcriptomes of PcJBC1 grown in MM under green light and dark condition. Among 243 differentially expressed genes (>2-fold change), the photoreceptor genes, bacteriophytochrome (bphP) and heme-oxygenase (bphO) were significantly up-regulated, whereas genes involved in the type 1 secretion system (T1SS), type 6 secretion system (T6SS), phytotoxic lipopeptides, and iron acquisition were profoundly repressed under green light. Corresponding to qPCR analysis, the RNA-seq results also showed no significant alteration in the T3SS- and flagellar-related genes. Overall, our results suggest that green light perceived by PcJBC1 plays a key role in diverse physiological responses that might affect this pathogen's epiphytic survival. The receptor and signaling network involved in green light perception should be identified in further investigation.