The role of TOR in autophagy regulation from yeast to plants and mammals

The target of rapamycin (TOR) is a conserved Ser/Thr kinase that controls cell growth by activating an array of anabolic processes including protein synthesis, transcription and ribosome biogenesis, and by inhibiting catabolic processes such as mRNA degradation and autophagy. Control of autophagy by TOR occurs primarily at the induction step, and involves activation of the ATG1 kinase, a conserved component of the autophagic machinery. A substantial number of genes participating in autophagy have been originally identified in yeast. Most of these genes have mammalian homologues and many have apparent homologues in plants, indicating that autophagy is conserved among eukaryotes. The recent identification of TOR as a key element in cell growth control in plants and algae opens the way for future studies to investigate whether this signaling pathway may also control autophagy in photosynthetic organisms.