Endophytic Pseudomonas oryzihabitans CB24 Boosts Photosynthesis Through Monogalactosyldiacylglycerol Driven Lipid Reprogramming

Pelargonium graveolens, valued for its essential oil, is significantly influenced by its endosymbiotic associations impacting its physiology and phytochemistry, though the exact mechanisms driving this modulation remain largely unexplored. This study unveils that inoculating Pseudomonas oryzihabitans CB24 into P. graveolens significantly alters plant's lipid dynamics, leading to increased accumulation of chloroplast glycerolipids like monogalactosyldiacylglycerol (MGDG) and sulfolipids, sulfoquinovosyldiacylglycerol (SQDG). This is achieved by enhancing precursors like UDP-6-sulfoquinovose and acetyl CoA, alongside upregulating genes such as plc, MGD1, and SQD2 crucial for glycerolipid metabolism. Glycerolipids being essential for thylakoidal membrane stability resulted in significant upregulation of genes related to antennae protein, light-harvesting complexes namely, LHCA2, LHCA1, PsaA, PetE, PetF, PsbO. P. oryzihabitans also boosted RuBisCO activity, thereby redirecting the metabolic flux towards secondary metabolism. Similarly, the upregulated expression of the DXS gene, which drives the precursors of the methylerythritol-phosphate (MEP) pathway to their end products such as monoterpenoids: geraniol and linalool, aligns with the metabolic shift from primary to secondary terpenoid biosynthesis. This transformative role of endophytic association highlights the remarkable ability of endophytes to regulate interconnected physiological processes, including improved nitrate uptake, enhanced carbon assimilation, and boosted antioxidant capacity driving significant improvements in growth, development and yield of the host plant.