The role of reticulophagy under early phase phosphate starvation in plant cells.

Inorganic phosphate (Pi) is one of the most important nutrients for plant growth. Under Pi starvation, intracellular components are degraded for Pi recycling in plant cells. Macroautophagy/autophagy is a process for vacuolar degradation of cytoplasmic components including organelles, but it is still unclear whether this process is involved in plant growth and Pi recycling during Pi starvation. Recently, we reported that the degradation of endoplasmic reticulum (ER) by selective autophagy, termed reticulophagy, contributes to Pi recycling and is an important stress response in the early phase of Pi starvation. During this phase, oxidized lipids are accumulated in the plant cell in an iron ion-dependent manner, and this accumulation causes ER stress which induces reticulophagy. As a result, the Pi contents are maintained at a sufficient level during early Pi starvation, suppressing any late Pi starvation responses, such as membrane lipid remodeling. Thus, we proposed that ER stress-induced reticulophagy is an important Pi salvage system during the early phase of Pi starvation in plants.