The photosynthetic bacteria delayed tomato leaf senescence under weak light conditions by regulating SlPIF4-SlIPT6/SlLOG8 module

Weak light threatens crop yield by impairing plant photosynthesis and growth. How to improve crop growth under such circumstances is extremely important for the agriculture and forestry. Photosynthetic bacteria can utilize bacteriochlorophyll to photosynthesize in weak light and anaerobic environments where plants cannot survive. Whether photosynthetic bacteria can be used to improve photosynthesis of plants under weak light environments has not been reported. Here, we found that foliar spraying of photosynthetic Rhodopseudomonas palustris strain CGA009 delayed leaf senescence and enhanced tomato photosynthesis under weak light conditions. Bacteria treatment maintained chlorophyll level by promoting the degradation of the negative regulator SlPIF4, which thereby relieved the repression of cytokinin biosynthesis genes SlIPT6/SlLOG8. Silencing of SlIPT6 and SlLOG8 made tomato plants insensitive to R. palustris treatment under weak light conditions, leading to a decrease in the synthesis of the active cytokinin N6-Isopentenyladenine (iP) and cis-Zeatin (cZ). Our findings demonstrated that R. palustris can rescue the photosynthetic capacity of tomatoes under weak light conditions through transcription regulation. Thus, this study provides an avenue to enhance crop yield under weak light stress by plant photosynthesis improvement mediated via photosynthetic bacteria.