Abstract
Autophagy is one of the mechanisms by which cells degrade their constituents under nutrient starvation conditions. It is mainly executed and controlled by ATG proteins. Autophagy contributes to a nutrient supply under starvation conditions and to the removal of denatured proteins. It has also been reported that autophagy plays a role in various reactions including immunity in mammalian cells. In plant cells, autophagy has been thought to carry out similar functions to mammalian cells. It is also suggested that autophagy has functions peculiar to plants. Although the ATG mutants of Arabidopsis undergo senescence earlier than those of wild type plants, the linking mechanism is not fully understood.
In the present study, to clarify the physiological functions of autophagy in plant cells, we have knocked out the ATG5 gene, an ATG gene essential for autophagy, in the moss Physcomitrella patens. The protonema cells of knockout mutants became yellow earlier than those of wild type plants, when they were cultured on a carbon starvation medium and on a phosphorus starvation medium. The result suggests that defect in autophagy leads to early senescence as has been reported in Arabidopsis.
