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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.

Pexophagy plays a pivotal role in the selective removal of ROS-generating peroxisomes, which protects plants from oxidative damage during photosynthesis under high-intensity light.

Phosphorus (P) is an essential nutrient for plant growth and plants use inorganic phosphate (Pi) as their P source, but its bioavailable form, orthophosphate, is often limited in soils. Hence, plants have several mechanisms for adaptation to Pi starvation. One of the most common response strategies is “Pi recycling” in which catabolic enzymes degrade intracellular constituents, such as phosphoesters, nucleic acids and glycerophospholipids to salvage Pi. Recently, several other intracellular degradation systems have been discovered that salvage Pi from organelles. Also, one of sphingolipids has recently been identified as a degradation target for Pi recycling. So, in this mini-review we summarize the current state of knowledge, including research findings, about the targets and degradation processes for Pi recycling under Pi starvation, in order to further our knowledge of the whole mechanism of Pi recycling.

Pine wilt disease (PWD) is an infectious disease of pines that typically kills affected trees. The causal pathogen of PWD is the pine wood nematode (PWN), Bursaphelenchus xylophilus. Understanding of the disease has advanced in recent years through the use of a highly sensitive proteomics procedure and whole genome sequence analysis; in combination, these approaches have enabled identification of proteins secreted by PWNs. However, the roles of these proteins during the onset of parasitism have not yet been elucidated. In this study, we used a leaf-disk assay based on transient overexpression in Nicotiana benthamiana to allow functional screening of 10 candidate pathogenic proteins secreted by PWNs. These proteins were selected based on previous secretome and RNA-seq analyses. We found that five molecules induced significant cell death in tobacco plants relative to a GFP-only control. Three of these proteins (Bx-TH1, Bx-TH2, and Bx-CPI) may have a role in molecular mimicry and likely make important contributions to inducing hypersensitive responses in host plants.