Abstract
Autophagy is a degradation system induced by nutrient limitation. We had 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 red fluorescent protein (RFP). Unfortunately this system has a limitation to monitor the kinetics of autophaic degradation because proteins synthesized before and after autophagy cannot be distinguished in this system. To improve this system we developed a system to use 'kikume', which is a photoconvertible fluorescent protein. The fluorescence of this protein is converted from green to red by radiating 360-410 nm light. We established a quantitative monitoring system of autophagic degradation in BY-2 cells by expressing a fusion protein of Cyt b5 and kikume. Using this system we found that tobacco cell does not stop protein synthesis immedietly after phosphate starvation. Under phosphate starvation proteins synthesized both before and after starvation are degraded by autophagy. Currently, we are elucidating the mechanism of nutrient-responsive autophagic degradation using this system.
