Multifaceted roles of plant glycosyl hydrolases during pathogen infections: more to discover.

Carbohydrates are hydrolyzed by a family of carbohydrate-active enzymes (CAZymes) called glycosidases or glycosyl hydrolases. Here, we have summarized the roles of various plant defense glycosidases that possess different substrate specificities. We have also highlighted the open questions in this research field. Glycosidases or glycosyl hydrolases (GHs) are a family of carbohydrate-active enzymes (CAZymes) that hydrolyze glycosidic bonds in carbohydrates and glycoconjugates. Compared to those of all other sequenced organisms, plant genomes contain a remarkable diversity of glycosidases. Plant glycosidases exhibit activities on various substrates and have been shown to play important roles during pathogen infections. Plant glycosidases from different GH families have been shown to act upon pathogen components, host cell walls, host apoplastic sugars, host secondary metabolites, and host N-glycans to mediate immunity against invading pathogens. We could classify the activities of these plant defense GHs under eleven different mechanisms through which they operate during pathogen infections. Here, we have provided comprehensive information on the catalytic activities, GH family classification, subcellular localization, domain structure, functional roles, and microbial strategies to regulate the activities of defense-related plant GHs. We have also emphasized the research gaps and potential investigations needed to advance this topic of research.