Chitin signaling and plant disease resistance

Abstract

Chitin, a polymer of N-acetyl-D-glucosamine, is a component of the fungal cell wall and is not found in plants. Plant cells are equipped with chitin degrading enzymes to digest fungal cell walls and are capable of perceiving chitin fragments (chitooligosaccharides) released from fungal cell walls during fungal infection. Chitin recognition results in the activation of defense signaling pathways. Although chitin is a well recognized pathogen-associated molecular pattern (PAMP), little is known about the molecular mechanism of chitin signaling. Recent studies identified a number of critical components in the chitin-elicited signaling pathway including a potential receptor, MAPK cascade and transcription factor network. Interestingly, the chitin signaling pathway overlaps with the phytobacterial flagellin-and EF-Tu-elicited signaling pathways, suggesting that plant cells may perceive different PAMPs from various pathogens via specialized receptors and then utilize a conserved, common downstream pathway to mediate disease resistance. Given the fact that fungal pathogens are major problems in many agricultural systems, research on chitin signaling could have significance to sustainable agriculture and biofuel and biomaterial production.

Keywords: CERK1; LysM RLK1; PAMP; chitin; chitooligosaccharide; innate immunity; signal transduction.

Figure 1

Chitin signaling pathway vs. flagellin-and EF-Tu-mediated pathways. Increasing evidence suggests these pathways share a common, downstream pathway to mediate plant innate immunity against different pathogens, although the initial stages are different, as partially reflected by different receptors. Blue circle: LysM motif, Yellow column: leucine-rich repeats; Red oval: kinase domain.