Receptor-mediated chitin perception in legume roots is functionally separable from Nod factor perception

Abstract

The ability of root cells to distinguish mutualistic microbes from pathogens is crucial for plants that allow symbiotic microorganisms to infect and colonize their internal root tissues. Here we show that and possess very similar LysM pattern-recognition receptors, LYS6/LYK9 and LYR4, enabling root cells to separate the perception of chitin oligomeric microbe-associated molecular patterns from the perception of lipochitin oligosaccharide by theNFR1/LYK3 and NFR5/NFP receptors triggering symbiosis. Inactivation of chitin-receptor genes in ,, and mutants eliminates early reactive oxygen species responses and induction of defense-response genes in roots., , and mutants were also more susceptible to fungal and bacterial pathogens, while infection and colonization by rhizobia and arbuscular mycorrhizal fungi was maintained. Biochemical binding studies with purified LYS6 ectodomains further showed that at least six GlcNAc moieties (CO6) are required for optimal binding efficiency. The 2.3-Å crystal structure of theLYS6 ectodomain reveals three LysM motifs similar to other LysM proteins and a conserved chitin-binding site. These results show that distinct receptor sets in legume roots respond to chitin and lipochitin oligosaccharides found in the heterogeneous mixture of chitinaceous compounds originating from soil microbes. This establishes a foundation for genetic and biochemical dissection of the perception and the downstream responses separating defense from symbiosis in the roots of the 80-90% of land plants able to develop rhizobial and/or mycorrhizal endosymbiosis.

Lipo‐chitooligosaccharide signalling blocks a rapid pathogen‐induced ROS burst without impeding immunity

“…However, attempts to underpin the involvement of NFP in the perception of pathogens showed that M. truncatula possesses other receptors to trigger ROS bursts and defence gene expression (Nars et al ., ; Rey et al ., ). This model is in line with recent elucidation of distinct signalling pathways for chitin triggered immunity and LCO mediated symbiotic responses in M. truncatula roots (Bozsoki et al ., ). In addition, our new data illustrate how these pathways cross‐talk at the level of ROS homeostasis but can function coincidentally.…”

Know your enemy, embrace your friend: using omics to understand how plants respond differently to pathogenic and mutualistic microorganisms

“…Bozsoki et al . () detail evidence that different sets of plant LysM receptor proteins exhibit specificity in being able to perceive rhizobial Nod factors from pathogenic MAMPs. The proteins CERK6 of Lotus and both LYK9 and LYR4 of Medicago do not perceive Nod factors but are instead able to bind pathogenic chitin oligomers, leading to a defensive response by the plant (Bozsoki et al ., ).…”

“…() detail evidence that different sets of plant LysM receptor proteins exhibit specificity in being able to perceive rhizobial Nod factors from pathogenic MAMPs. The proteins CERK6 of Lotus and both LYK9 and LYR4 of Medicago do not perceive Nod factors but are instead able to bind pathogenic chitin oligomers, leading to a defensive response by the plant (Bozsoki et al ., ). In all cases, altered expression of these proteins or mutations to these proteins lead to differences in pathogen susceptibility without any impact on rhizobial nodulation and symbiosis (Bozsoki et al ., ).…”

Chitin and chitin-related compounds in plant–fungal interactions

“…While the results indicated the involvement of partially homologous plasma membrane proteins (RLK1 and NFR) both in defence and symbiotic signalling in plant cells (Kaku et al 2006), Bozsoki et al (2017) revealed that distinct receptor sets respond to chitin and lipochitin oligosaccharides in Lotus japonicus and Medicago truncatula legume roots separating defence from the symbiosis of the roots.…”