Abstract
Autophagy is a degradation system induced by nutrient limitation. We have developed a quantitative monitoring system of autophagic degradation in transformed tobacco BY-2 cells, which express a fusion protein of cytochrome b5 (Cyt b5) and a photo-convertible fluorescent protein (Kikume). Using this system we found that tobacco cell does not stop protein synthesis immediately after phosphate limitation. Under phosphate starvation proteins synthesized both before and after starvation were degraded by autophagy.
To compare the mechanism of the induction of autophagy under phosphate, sugar and nitrogen limitation conditions, we conducted experiments including phosphite under starvation conditions. We found that phosphite in phosphate starvation is effective in delaying the induction of autophagy. This result was also shown by analysis of the stability and degradation of Atg8, which is a marker protein of autophagosomes. Interestingly, we could not find any effect of phosphite on nitrogen- and sucrose-starvation conditions. Thus the signal transduction pathways of nutrient-responsive autophagy induction varied on the type of nutrients.
