ИСТИНА

Multiple environmental stimuli regulate the life cycle of budding yeast Saccharomyces cerevisiae. The deficiency of nitrogen source inhibits budding and favors the formation of elongated cells – pseudohyphae. This process correlates with the increase of duration of cell cycle G2 phase and can be upregulated by repression of protein phosphatase Mih1. Mitochondria also influence this developmental transition: yeast cells lacking mitochondrial DNA are not capable to form pseudohyphae [1]. We found that uncoupler carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP), but not the inhibitor of ATP-synthase oligomycin D prevented pseudohyphae formation induced by butanol [2]. Moreover, a fraction of mitochondria within each pseudohyphal cell appeared to be hyperpolarized. One explanation is that hyperpolarized mitochondria produce hydrogen peroxide which subsequently inactivates Mih1p. Indeed, Mih1p can be easily inactivated by hydrogen peroxide [3]. At the same time, it was found that retrograde signaling pathway is a positive regulator of pseudohyphae formation. The mitochondria with low transmembrane potential activate Rtg2p which subsequently induces relocalization of Rtg1p and Rtg3p from cytoplasm to the nucleus [4]. We have found that the deletion of either RTG1, RTG2 or RTG3 gene decreases the number of pseudohyphal cells in SLAD medium supplemented with butanol. Therefore, the formation of pseudohyphae by yeast requires two subpopulations of mitochondria: one with high and another with low transmembrane potential. The heterogenous subpopulations of mitochondria within individual cells also can be observed under other stressful conditions. We suggest that such heterogeneity could be important for selective autophagy of mitochondria and stress resistance.