Hide-and-Seek: Chitin-Triggered Plant Immunity and Fungal Counterstrategies

Fungal pathogens are major destructive microorganisms for land plants and pose growing challenges to global crop production. Chitin is a vital building block for fungal cell walls and also a broadly effective elicitor of plant immunity. Here we review the rapid progress in understanding chitin perception and signaling in plants and highlight similarities and differences of these processes between arabidopsis and rice. We also outline moonlight functions of CERK1, an indispensable chitin coreceptor conserved across the plant kingdom, which imply potential crosstalk between chitin signaling and symbiotic or biotic/abiotic stress signaling in plants via CERK1. Moreover, we summarize current knowledge about fungal counterstrategies for subverting chitin-triggered plant immunity and propose open questions and future directions in this field. Chitin perception systems in both arabidopsis and rice consist of multiple LysM-containing proteins, which undergo chitin-induced oligomerization to trigger intracellular signaling. An oligomer size-dependent chitin sensing mechanism is conserved across plants and mammals.Receptor-like cytoplasmic kinase VII members are essential players of chitin signaling in both arabidopsis and rice.Both arabidopsis and rice CERK1 proteins play multifaceted functions beyond chitin signaling and may mediate the crosstalk between chitin signaling and symbiotic or other biotic or abiotic stress signaling.Most uncovered fungal countermeasures to subvert chitin-triggered plant immunity involve blocking the generation and perception of chitin oligomers in plant apoplast, whereas fungal cytoplasmic effector-mediated strategies to disrupt chitin signaling inside plant cells remain poorly understood.