Autophagy-assisted glycogen catabolism regulates asexual differentiation inMagnaporthe oryzae

Abstract

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 riceblast 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 Moatg8Δ 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.

Sorting nexin Snx41 is essential for conidiation and mediates glutathione-based antioxidant defense during invasive growth inMagnaporthe oryzae

“…3D). The N-terminal RFP tag was likely cleaved from the RFP-Atg8 fusion protein and accumulated in the vacuoles upon nitrogen starvation, 10 indicating proper fusion of autophagosomes with the vacuole in snx41D. This result further supported the conclusion that autophagy was active and functional in the snx41D mutant.…”

“…We had earlier reported that autophagyassisted glycogen catabolism is necessary for Magnaporthe conidiation, but could be bypassed by exogenous supplementation with sucrose or glucose 6-phosphate (G6P) in the atg8D mutant. 10 External addition of sucrose or G6P could also suppress the conidiation defects in another autophagy-deficient mutant, atg1D (Fig. S3A), further confirming the importance of glycogen autophagy in carbon homeostasis during Magnporthe conidiation.…”

“…Autophagy is required for proper conidiation in Magnaporthe, wherein it assists carbohydrate metabolism to meet the energy requirements during cellular differentiation. 10 Magnaporthe snx41D mutant displayed more severe defects in conidiation compared with the autophagy-deficient atg8D, and such defects could not be restored by exogenous glucose, indicating that Snx41 may play a different function than autophagy-assisted nutrient catabolism. 10,11 By systematic characterization, we have shown that the nonselective autophagy was normal in the snx41D mutant.…”

“…10 Magnaporthe snx41D mutant displayed more severe defects in conidiation compared with the autophagy-deficient atg8D, and such defects could not be restored by exogenous glucose, indicating that Snx41 may play a different function than autophagy-assisted nutrient catabolism. 10,11 By systematic characterization, we have shown that the nonselective autophagy was normal in the snx41D mutant. However, pexophagy, the selective autophagic degradation of peroxisomes, was delayed/blocked in the snx41D mutant.…”

“…9 More recently, we showed that autophagy is induced during Magnaporthe conidiation, wherein it facilitates carbon catabolism and nutrient homeostasis. 10,11 Autophagy is a bulk degradation process conserved in the eukaryotic cells. It was first identified by electron microscopy and considered as nonselective for its cytosolic cargos.…”