Functions Of LYKs In Chitin-induced Immunity In Arabidopsis

Chitin is the second most abundant polysaccharide which is widely distributed in the shell of crustaceans,the skeleton of insects and the major component of cell wall of fungi.Chitin could be recognized by plants to initiate innate immune responses against the invasion of countless foreign pathogens.In terms of chemical structure,chitin is a polymer of ?-1,4-linked-N-acetylglucosamine,among which the oligosaccharide chains with a degree of polymerization of 6-8 are well characterized to effectively induce strong innate immune responses in plants.The Lys M receptor kinases(LYKs)family are well identified as chitin receptors in Arabidopsis thaliana.There are five protein members in this family.Among them,LYK1/CERK1 and LYK5 are major receptors to recognize and bind to chitin in Arabidopsis.The receptor complex transduces chitin signals to downstream components via the kinase activity of CERK1.However,the functions of other protein members in the LYKs family and the specific relationships between them are still unclear.This study explores the specific functions played by other protein members of LYKs family in mediating chitin immune signals.We found that CERK1 plays a major role in mediating chitin signals,and the function of LYK5 is weaker than that of CERK1 but it still plays an important role than other receptor protein members of LYKs in Arabidopsis.LYK3 and LYK4 also play a role in this signaling pathway,but their functions are relatively weaker than those of CERK1 and LYK5.At the same time,we found a downstream protein HSP1 which interacts with CERK1 transducing chitin signals.HSP1 belongs to the small Heat Shock Proteins(s HSPs)family.hsp1-4 loss-of-function mutant was constructed in Arabidopsis using CRISPR-Cas9 technology.Subsequently,we showed that it plays a positive regulatory role in the processing or modification of CERK1 receptor protein and affect the chitin immune signal transduction by detecting the expression of CERK1 and MAPK in hsp1-4 loss-of-function mutant.In addition,we found that there were different effects between chitin and chitooctaose in triggering the immune response in Arabidopsis.This study reveals the relationships between the chitin receptor LYKs family and the specific functions of them in transducing immune signals in Arabidopsis,which is helpful for us to understand the molecular mechanism of plant immune system triggered by chitin.So that the advantages of plant immune system can be applied in agricultural production to improve the ability of crops resisting insects and plant diseases by combining theory with practice.