Three consecutive glycolysis enzymes are involved in autophagic flux regulation through monitoring nutrient availability
Autophagy serves as an important recycling route for growth and survival of eukaryotic organisms in nutrient-deficient conditions. When confronted with starvation, metabolic flux is coordinated by individual metabolic enzymes. Given that the metabolic diversity of carbon in eukaryotes is related to their lifestyle, autophagy may be modulated by metabolic enzymes by monitoring carbon flux. Here, we attempted to identify carbon metabolic genes that modulate autophagy using VIGS screening of 45 glycolysis- and the Calvin-Benson cycle-related genes. We report here that three consecutive triose-phosphate-processing enzymes involved in the cytosolic glycolysis, TPI (triose-phosphate-isomerase), GAPC (glyceraldehyde-3-phosphate dehydrogenase), and PGK (phosphoglycerate kinase), designated TGP, negatively regulate autophagy. Depletion of TGP enzymes result in spontaneous autophagy induction and increases ATG1 kinase activity. TGP enzymes interact with ATG101, a regulatory component of the ATG1 kinase complex. Spontaneous autophagy induction and abnormal growth under insufficient sugar in the TGP mutants is suppressed by crossing with the atg101 mutant. Considering that triose-phosphates are photosynthates transported to the cytosol from active chloroplasts, the TGP enzymes may be strategically positioned to monitor the flow of photosynthetic sugars and modulate autophagy accordingly. Collectively, these results suggest that TGP enzymes negatively control autophagy acting upstream of the ATG1 complex, which is critical for seedling development.