title: A vacuolar glucoamylase, Sga1, participates in glycogen autophagy for proper asexual differentiation in Magnaporthe oryzae.
abstract: Nutrient limitation acts as a trigger for the synthesis of glycogen, which serves as a carbon and energy reserve during starvation. Recently, we reported that an autophagy-deficient mutant (atg8Δ) shows severe reduction in aerial hyphal growth and conidiation in the rice-blast fungus Magnaporthe oryzae, and proposed that autophagy plays an important role in facilitating glycogen homeostasis to ensure proper asexual differentiation in Magnaporthe. Here, we identify and characterize a vacuolar glucoamylase function (Sga1) that hydrolyses glycogen to meet the energy requirements during asexual development in Magnaporthe. Loss of SGA1 resulted in significant reduction in conidiation compared to the wild-type Magnaporthe strain. More importantly, an sga1Δ atg8Δ double deletion mutant showed further reduction in conidiation compared to the atg8Δ mutant in Magnaporthe. Forced localization of GFP-Sga1 to the cytoplasm (through removal of the predicted signal peptide) led to increased conidiation in wild type and the sga1Δ, but more interestingly, significantly restored conidiation in the atg8Δ mutant. Our results indicate that autophagy and Sga1 act cooperatively in vacuolar glycogen breakdown, which is essential for conidia formation but dispensable for pathogenicity in Magnaporthe.
authors.affiliation: Fungal Patho-Biology Group, Temasek Life Sciences Laboratory, and Department of Biological Sciences; National University of Singapore, Singapore.
authors.forename: Yi Zhen
authors.initials: YZ
authors.lastname: Deng
authors.forename: Naweed I
authors.initials: NI
authors.lastname: Naqvi
mesh_terms: D001343:Autophagy; D055162:Biocatalysis; D005656:Fungal Proteins / Q000378:metabolism*; D005087:Glucan 1,4-alpha-Glucosidase / Q000378:metabolism*; D006003:Glycogen / Q000378:metabolism*; D006868:Hydrolysis; D020082:Magnaporthe / Q000166:cytology* / Q000201:enzymology* / Q000502:physiology; D021381:Protein Transport; D012100:Reproduction, Asexual / Q000502:physiology*; D013172:Spores, Fungal / Q000254:growth & development; D013347:Subcellular Fractions / Q000201:enzymology; D014617:Vacuoles / Q000201:enzymology
chemical_list: D005656:Fungal Proteins; D006003:Glycogen; D005087:Glucan 1,4-alpha-Glucosidase