Plant cells recognize chitin fragments for defense signaling through a plasma membrane receptor

Abstract

elicitor ͉ host-pathogen interaction ͉ N-acetylchitooligosaccharides ͉ pathogen-associated molecular patterns H igher plants have the ability to initiate various defense reactions such as hypersensitive responses, production of phytoalexins and antimicrobial proteins, and reinforcement of cell walls when they are infected by various pathogens (1, 2). They can distinguish self and non-self, or detect specific pathogens, through the perception of signal molecules (elicitors) mostly generated͞secreted from pathogens. Fragments of cell surface macromolecules typical of microorganisms such as cell wall polysaccharides, secreted proteins, as well as a flagella protein, often serve as a potent elicitor to induce defense reactions. They are classified as ''general elicitors'' that are commonly found in various microorganisms and induce defense responses in a wide range of plant species. Perception of general elicitors has been thought to play an important role in the basic resistance, or nonhost resistance, of plants to most potential pathogens. It has also been emerged in recent years that the defense systems mediated by the perception of these ''general elicitors'' have a considerable similarity with mammalian innate immunity, in the recognition of pathogen-associated molecular patterns as well as the molecules involved in the perception and transduction of these signal molecules (3).Chitin oligosaccharides (N-acetylchitooligosaccharides) are a representative general elicitor inducing defense responses in a wide range of plant cells including both monocots and dicots (4). Chitin oligosaccharides were reported to induce defense responses also in mammalian and insect cells (4, 5). Interestingly, specific modifications of chitin oligosaccharides by fatty acids, sulfate, or some sugars, generate ''Nod factors'' that induce nodulation in legume roots in the symbiotic interaction with rhizobial bacteria (6). Thus, the recognition of chitin oligosaccharides and related compounds seems to play a fundamental role in the establishment of basal resistance to potential pathogens in plants and in some cases the symbiotic relationships between leguminous plants and rhizobial bacteria.Concerning to the receptor for chitin oligosaccharide elicitor, we previously identified a high-affinity binding protein for this elicitor in the plasma membrane of rice cells by affinity labeling (7). Similar binding proteins were also detected in various plant cells that could respond to the elicitor (8,9). Correlation between the presence of the binding proteins and the elicitor responsiveness of these cells, correlation between the binding specificity and the preference of the structure of chitin oligosaccharides in defense responses, strongly indicated that the binding proteins function as a receptor, or a part of receptor complex, for chitin oligosaccharide elicitor. Here we report the purification of this chitin oligosaccharide elicitor-binding protein (hereafter designated as CEBiP), cloning of the corresponding cDNA and its functional characte...

How rhizobial symbionts invade plants: the Sinorhizobium–Medicago model

“…This response helps plants defend themselves against fungal attack, as chitin is a component of fungal cell walls 124 . Intriguingly, the chitin receptor of rice (Oryza sativa) is a LysM-domain-containing protein, as are the Nod factor receptors MtNFP and MtLYK3 131 . One possibility is that plant proteins containing extracellular, chitininteracting LysM domains were co-opted in the legume lineage to recognize bacterially produced lipochitooligosaccharide Nod factors.…”

Chitin and chitin-related compounds in plant–fungal interactions

“…Investigation of the molecular mechanism of chitin perception and chitin-triggered immunity in plants flourished since the cloning of the first plant chitin oligosaccharide receptor CEBiP (chitin elicitor-binding protein), a plasma membrane glycoprotein from rice (Kaku et al 2006). CEBiP is typical receptor-like protein (RLP) with an extracellular domain containing two predicted lysin motifs (LysMs) at the N terminus and a short membrane-spanning domain at the C terminus and lacks cytoplasmic kinase domain but directly involved in chitin-triggered immunity (Kouzai et al 2014).…”

“…The LysM motif is known to exist in the putative Nod-factor receptor kinases involved in the symbiotic signalling between leguminous plants and rhizobia (Desaki et al 2017). Chitin-oligomers from fungal pathogens are structurally like lipo-chito-oligosaccharide Nod factors produced by rhizobia, and LysM RLK1 (Wan et al 2008) or CERK1 (Miya et al 2007) is homologous to legume Nod factor receptors (NFR) NFR1 and NFR5 (Kaku et al 2006). …”

“…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.…”

Glycan moiety of flagellin inAcidovorax avenaeK1 prevents the recognition by rice that causes the induction of immune responses

“…5,6,7,8 PAMPs include structures characteristic from pathogens such as b-glucan, polysaccharide chitin, ergosterol, lipopolysaccharides (LPS), flagellin and elongation factor-Tu. 9,10,11,12 Among these PAMPs, flagellin, a main component of the bacterial flagellum, has been the most extensively studied in regards to the recognition mechanism and signal transduction. 13,14,15,16 We previously reported that flagellin from the rice avirulent N1141 strain of gram-negative phytopathogenic bacterium, Acidovorax avenae, induces PTI including H 2 O 2 generation, while flagellin from the rice virulent K1 strain of A. avenae does not induce.…”