Lag-phase autophagy in the methylotrophic yeast Pichia pastoris

When microbes sense environmental changes, they often temporarily attenuate cell growth to adapt to the new situations, showing a lag phase. In this study, we report that the methylotrophic yeast, Pichia pastoris, induced autophagy during the lag phase after the cells were shifted from glucose to methanol medium. Through the autophagic process at least two proteins, aminopeptidase I precursor and cytosolic aldehyde dehydrogenase, were found to be transported into the vacuole, which was dependent on PpAtg11 and PpAtg17, respectively. Notably, PpAtg1 and PpAtg17 were required for early exit from the lag phase during the methanol adaptation. In accordance, phosphorylation states of elongation initiation factor 2alpha indicated reductions of intracellular amino-acid pools in the atg mutant strains. Together, these data demonstrate the importance of amino acid recycling by autophagy during a cell-remodeling process.