Autophagy-assisted glycogen catabolism regulates asexual differentiation in Magnaporthe oryzae

Autophagy, a conserved pathway for bulk cellular degradation and recycling in eukaryotes, regulates proper turnover of organelles, membranes and certain proteins. Such regulated degradation is important for cell growth and development particularly during environmental stress conditions, which act as key inducers of autophagy. We found that autophagy and MoATG8 were significantly induced during asexual development in Magnaporthe oryzae. An RFP-tagged MoAtg8 showed specific localization and enrichment in aerial hyphae, conidiophores and conidia. We confirmed that loss of MoATG8 results in dramatically reduced ability to form conidia, the asexual spores that propagate rice-blast disease. Exogenous supply of glucose or sucrose significantly suppressed the conidiation defects in a MoATG8-deletion mutant. Comparative proteomics based identification and characterization of Gph1, a glycogen phosphorylase that catalyzes glycogen breakdown, indicated that autophagy-assisted glycogen homeostasis is likely important for proper aerial growth and conidiation in Magnaporthe. Loss of Gph1, or addition of G6P significantly restored conidiation in the Moatg8Delta mutant. Overproduction of Gph1 led to reduced conidiation in wild-type Magnaporthe strain. We propose that glycogen autophagy actively responds to and regulates carbon utilization required for cell growth and differentiation during asexual development in Magnaporthe.