Light and chloroplast redox state modulate the progression of tobacco leaf infection by Pseudomonas syringae pv tabaci
Light significantly influences plant stress responses, with chloroplasts playing a pivotal role as both energy providers and light sensors. They communicate with the nucleus through retrograde signals, including secondary metabolites and reactive oxygen species (ROS). To investigate the contribution of chloroplast redox biochemistry to biotic responses, we studied the interactions of tobacco leaves expressing the alternative electron shuttle flavodoxin with virulent and nonhost Pseudomonas syringae pathovars under light and dark conditions. Flavodoxin is reported to limit light-dependent ROS propagation and over-reduction of the photosynthetic electron transport system under stress. Light intensified the hypersensitive response against the nonhost pathovar tomato (Pto), but slowed disease progression caused by the virulent pathovar tabaci (Pta). Flavodoxin mitigated light responses during both interactions, including decreased ROS levels, reduced stromule occurrence, and lower phytoalexin production, with different signatures depending on the pathovar. Similar leaf metabolic profiles were observed in the dark for both strains, with a general up-regulation of sugars, metabolic intermediates, and amino acids. In the light, instead, Pta increased sugars and intermediates, while Pto decreased them. Our results suggest that HR-like responses are elicited in the light even during virulent interactions, and that light effects are related to signals originating at the photosynthetic machinery. Highlights- Light inhibits disease progression during a tobacco-Pseudomonas virulent interaction. - Light exacerbates the hypersensitive response (HR) during a nonhost interaction. - HR-like responses are elicited in the light even during virulent interactions. - Plastid-targeted flavodoxin decreases plant damage only in photoperiod. - The chloroplast redox state modulates plant biotic response.