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Inhibition of Target of Rapamycin signaling and stress activate autophagy in Chlamydomonas reinhardtii

IBVF

María Esther Pérez-Pérez, Francisco J. Florencio, José L. Crespo Plant Physiology 2010, Vol. 152, 1874-1888

Autophagy is a catabolic membrane-trafficking process whereby cells recycle cytosolic proteins and organelles under stress conditions or during development. This degradative process is mediated by autophagy-related (ATG) proteins which have been described in yeasts, animals and more recently in plants. In this study we report the molecular characterization of autophagy in the unicellular green alga Chlamydomonas reinhardtii. We demonstrate that the ATG8 protein from Chlamydomonas (CrATG8) is functionally conserved and may be used as a molecular autophagy marker. Like yeast ATG8, CrATG8 is cleaved at the C-terminal conserved Glycine and is associated with membranes in Chlamydomonas. Cell aging or different stresses such as nutrient limitation, oxidative stress or the accumulation of misfolded proteins in the endoplasmic reticulum caused an increase in CrATG8 abundance as well as the detection of modified forms of this protein, both landmarks of autophagy activation. Furthermore, rapamycin-mediated inhibition of the TOR signaling pathway, a major regulator of autophagy in eukaryotes, results in identical effects on CrATG8 and a re-localization of this protein in Chlamydomonas cells similar to the one observed upon nutrient limitation. Thus, our findings indicate that Chlamydomonas cells may respond to stress conditions by inducing autophagy via TOR signaling modulation.

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