Recognition of Exogenous Lipids in Plant Immunity

Plants perceive diverse extracellular molecules derived from microbes and insects and activate immune responses. While significant progress has been made in understanding plant recognition of microbial proteins and carbohydrates such as chitin, the mechanisms underlying lipid recognition have remained largely elusive. Lipids are essential components of cells, and various microbe- and insect-derived lipid molecules have been reported to induce or modulate immune responses in plants. Recent findings have revealed that lipid perception involves not only canonical receptor-mediated recognition but also the sensing of changes in membrane-associated properties, highlighting the diverse mechanisms underlying lipid-mediated immune regulation. This review focuses on naturally occurring microbial and insect lipids that trigger plant defense responses upon exogenous application. Particular emphasis is placed on plasma membrane-localized lipid receptors identified to date, as well as receptor-independent mechanisms whereby changes in plasma membrane biophysical properties are directly perceived and translated into immune activation. This review provides an overview of recent findings on plant lipid perception and discusses unresolved issues and future directions in this field.