Plant phosphatidylinositol‐specific phospholipase C at the center of plant innate immunity

Understanding plant resistance to pathogenic microbes requires detailed information on the molecular mechanisms controlling the execution of plant innate immune responses. A growing body of evidence places phosphoinositide‐specific phospholipase C (PI‐PLC) enzymes immediately downstream of activated immune receptors, well upstream of the initiation of early defense responses. An increase of the cytoplasmic levels of free Ca²⁺, lowering of the intercellular pH and the oxidative burst are a few examples of such responses and these are regulated by PI‐PLCs. Consequently, PI‐PLC activation represents an early primary signaling switch between elicitation and response involving the controlled hydrolysis of essential signaling phospholipids, thereby simultaneously generating lipid and non‐lipid second messenger molecules required for a swift cellular defense response. Here, we elaborate on the signals generated by PI‐PLCs and their respective downstream effects, while providing an inventory of different types of evidence describing the involvement of PI‐PLCs in various aspects of plant immunity. We project the discussed information into a model describing the cellular events occurring after the activation of plant immune receptors. With this review we aim to provide new insights supporting future research on plant PI‐PLCs and the development of plants with improved resistance.