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Phosphoinositide-specific phospholipase C (PI-PLC) is a signaling enzyme that hydrolyzes membrane phosphoinositide 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)-responsive genes suggesting disrupted hormone signaling. Consistent with PLC role during 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 localizes predominantly at the plasma membrane. Upon P. infestans inoculations, SlPLC2-GFP localizes to the membrane surrounding infection vesicles, where we also detected phosphoinositides PI4P and PI(4,5)P₂. Overexpression of SlPLC2 in Nicotiana benthamiana enhanced susceptibility to P. infestans , reinforcing its positive role in colonization. Together, these findings identify SlPLC2 as a susceptibility factor associated with enhanced P. infestans colonization.

Statement

This study identifies SlPLC2 as a key susceptibility factor that supports Phytophthora infestans infection by coordinating vesicle formation and early immune responses in tomato.