Preliminary Studies On The Function Of Extracellular Cellulase PsGH7c From Phytophthora Sojae

Oomycetes are filamentous eukaryotic microorganisms with no septa and multinucleus.Although their morphology is similar to fungi,oomycetes are closer to lower algae in genetic evolution.Therefore,traditional fungicides have no effect on oomycetes.Oomycetes are closely related to plant diseases and can cause a variety of devastating diseases.Therefore,an in-depth understanding of its pathogenic process and infection mechanism will help to deeply understand the mechanism of plant disease resistance and develop new biological pesticides.Plant pathogenic bacteria secrete a variety of cell wall degrading enzymes(CWDEs)to destroy host cell wall components,such as cellulase,hemicellulase,etc.,as an important strategy for their active invasion of plants.Cellulose is an important component of plant cell walls.Cellulase is a glycoside hydrolase(Glycoside Hydrolase,GH).Cellulase is known to be distributed in at least 17 GH families.Among them,the function of the GH7 family has evolved very rapidly,containing exo-cellulase and endo-cellulase.Exo-cellulase can degrade crystalline cellulose with high efficiency.It is known that plant crystalline cellulose is a key area of the cell wall’s anti-degradation barrier and can only be hydrolyzed by exo-cellulase,so the exo-cellulase secreted by pathogenic bacteria is an important virulence factor.In this study,PsGH7c,selected from the Phytophthora sojae GH7 family,is an extracellular cellobiohydrolase,which acts on the ends of cellulose molecules to hydrolyzeβ-1,4-glycosidic bonds and is a kind of biodegradable cellulose.Important exonuclease.Cellulase secreted by pathogenic bacteria can be used as pathogen-associated molecular patterns(PAMPs)to induce immune response in host plants.Transmembrane receptors located on the cell surface will recognize specific conservative peptides of PAMPs,causing PTI(PAMP-Triggered Immunity)in plants.This experiment found that PsGH7c can cause tobacco cell death.It is speculated that PsGH7c is a new type of PAMP that can cause host immune responses.PsGH7c,as a class of extracellular cellulose exonuclease,its enzymatic activity helps to promote the infection of Phytophthora.The site-directed mutation of PsGH7c enzyme activity site found that the mutant enzymatic hydrolysis activity was significantly reduced,and the mutant could not cause host immune response,nor could it promote Phytophthora infection,indicating that PsGH7c’s promotion of Phytophthora infection depends on its hydrolytic activity.At the same time,the results also indicate that PTI triggered by PsGH7c is caused by the product of its hydrolysis of the cell wall,rather than the enzyme protein itself.This study found that the extracellular cellobiohydrolase PsGH7c in the Phytophthora sojae GH7 family is an important virulence factor.The in-depth study of the mechanism of PsGH7c is helpful to understand the pathogenic process and infection mechanism of Phytophthora sojae.Control strategies and molecular breeding for disease resistance provide a research basis.