Recycling of iron via autophagy is critical for the transition from glycolytic to respiratory growth.
Autophagy is a bulk degradation process conserved from yeast to mammals. To examine the roles of autophagy in cellular metabolism, we generatedautophagy-defective (atg) mutants in the X2180-1B strain background. We compared the growth of wild-type (WT) andatgcells in minimal (synthetic dextrose, SD) and rich (yeast extract/peptone/dextrose, YEPD) medium, and we found that mutations in the core autophagy machinery result in defects in the diauxic shift, the transition from fermentation to respiratory growth upon glucose depletion, specifically in SD. Furthermore, we confirmed that autophagy was induced prior to the diauxic shift, implying that it plays a role in this process. In YEPD,atgmutants grew normally, so we assumed that the insufficiency of certain nutrients in SD was responsible for the defects. We ultimately identified iron, which is a necessary cofactor for respiratory activity, as the nutrient required for the diauxic shift inatgmutants. Indeed,atgmutants exhibited defects in respiration, which was rescued by supplementation with iron. Based on these data, we hypothesized that autophagy is involved in iron recycling during the diauxic shift.smf3Δfet5Δ orsmf3Δftr1Δ cells, which are unable to export iron from the vacuole, also exhibit defects in the diauxic shift, so iron released from the vacuole is important for the shift in SD medium. Finally, we observed thatsmf3Δfet5Δ cells accumulated nearly twice as much vacuolar iron assmf3Δfet5Δatg2Δ cells, suggesting that autophagy is involved in iron recycling by the vacuolar transport and degradation of iron-containing cargos.
Research Unit for Cell Biology, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama 226-8503; Research Center for Odontology, School of Life Dentistry at Tokyo, The Nippon Dental University, Chiyoda-ku, Tokyo 102-8159, Japan.
Tetsuro
T
Horie
Research Unit for Cell Biology, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama 226-8503.
Tomoko
T
Kawamata
Research Unit for Cell Biology, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama 226-8503.
Miou
M
Matsunami
Research Unit for Cell Biology, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama 226-8503. Electronic address: yohsumi@iri.titech.ac.jp.
Yoshinori
Y
Ohsumi
D001343:Autophagy / Q000502:physiology*; D017353:Gene Deletion; D006019:Glycolysis / Q000502:physiology*; D007501:Iron / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism
D029701:Saccharomyces cerevisiae Proteins; D007501:Iron
autophagy; iron; mitochondria; respiration; vacuole; yeast