Functional analysis of an alpha-1,2-mannosidase from Magnaporthe oryzae.

Identification of enzymes that are expressed during host colonization and characterization of their biochemical properties are prerequisite to understanding their role in the pathogen-host interaction. Nine alpha-1,2-mannosidase homologs were identified in the analysis of the Magnaporthe oryzae genome. Endoplasmic reticulum localized alpha-1,2-mannosidases play an important role in protein glycosylation. However, several members of the alpha-1,2-mannosidase gene family are predicted to be secreted. The biological role of such extracellular enzymes in host colonization has not been defined. Here, we characterized a secreted alpha-1,2-mannosidase of M. oryzae, MGG_00994.6, and found that the mature polypeptide is a glycoprotein capable of hydrolyzing alpha-1,2 linked mannobiose. The gene is expressed during growth in vitro and during colonization on rice plants, however, deletion of the gene did not affect pathogenicity. Five other members of the alpha-1,2-mannosidase of M. oryzae were expressed with a pattern similar to MGG_00994.6, suggesting the potential for functional redundancy. These results form the basis for additional studies on the role of this gene family in the rice blast fungus and its interaction with rice.