Phytoplasma infection alters polar lipid composition and triggers chloroplast autophagy in host plants

Phytoplasmas are small, cell wall-less bacteria that infect a wide range of plant species. In this study, changes in the polar lipid composition of tomato plants infected with potato purple top (PPT) phytoplasma were investigated. The analysis revealed a decrease in the levels of monogalactosyldiacylglycerol (MGDG), phosphatidic acid, and phosphatidylglycerol in PPT phytoplasma-infected plants compared to controls. The MGDG/digalactosyldiacylglycerol ratio, an indicator of chloroplast thylakoid membrane structure and function, was reduced in PPT phytoplasma-infected plants. Additionally, the degradation of the chloroplast rubisco large and small subunits (RbcL and RbcS) was observed in infected plants, indicating the activation of chloroplast autophagy triggered by the accumulation of reactive oxygen species resulting from lipid composition changes. These findings suggest that PPT phytoplasma infection alters the lipid metabolism of host plants, which could contribute to development of yellowing symptoms and reduced photosynthesis efficiency. Understanding these mechanisms could lead to the development of new disease control strategies.