Phosphoinositide-specific Phospholipase C 2 (SlPLC2) Facilitates Vesicle Formation and Modulates Immune Signaling in Tomato Phytophthora infestans Interactions

Phosphoinositide-specific phospholipases C (PI-PLC) are signaling enzymes that hydrolyze membrane phosphoinositides to generate lipid- and lipid-derived second messengers. In plants, PI-PLCs have been implicated in various physiological processes, including immunity. Tomato SlPLC2 was previously shown to be implicated in susceptibility to the necrotrophic fungus Botrytis cinerea. However, whether this observation extends to pathogens with different lifestyles and evolutionary origins remains unknown. Here, we investigated SlPLC2 function during infection with Phytophthora infestans, a globally devastating oomycete and causal agent of potato and tomato late blight. CRISPR-Cas9 knockout SlPLC2 plants showed significantly reduced disease symptoms, lower pathogen biomass, and decreased sporangia production, indicating impaired colonization. Upon infection, SlPLC2 knockout lines displayed attenuated expression of salicylic acid (SA)- and jasmonic acid (JA)-marker genes. Consistent with a role for PLC signalling in plant defense, early immune responses such as hydrogen peroxide accumulation and callose deposition were reduced in knockout plants. At the cellular level, these plants allow fewer infection vesicles formation by P. infestans, accompanied by an increase in expression of a biotrophy-associated effector gene PiAvrblb2, suggesting impaired establishment of infection. In Nicotiana benthamiana, SlPLC2-GFP displays a localization pattern predominately consistent with plasma membrane association and also localizes to the membranes surrounding P. infestans infection vesicles, where we also detected phosphoinositides PI4P and PI(4,5)P₂. As complementary heterologous evidence, transient overexpression of SlPLC2 in Nicotiana benthamiana enhanced lesion development after P. infestans inoculations. Together, these findings identify SlPLC2 as a susceptibility factor associated with enhanced P. infestans colonization.