A mechanism implicating plastoglobules in thylakoid disassembly during senescence and nitrogen starvation.

Plastoglobules are lipid droplets present in all plastid types. In chloroplasts, they are connected to the thylakoid membrane by the outer lipid half-bilayer. The plastoglobule core is composed of neutral lipids most prominently the prenylquinones, triacylglycerols, fatty acid phytyl esters but likely also unknown compounds. During stress and various developmental stages such as senescence, plastoglobule size and number increase due to the accumulation of lipids. However, their role is not limited to lipid storage. Indeed, the characterization of the plastoglobule proteome revealed the presence of enzymes. Importantly it has been demonstrated that these participate in isoprenoid lipid metabolic pathways at the plastoglobule, notably in the metabolism of prenylquinones. Recently, the characterization of two phytyl ester synthases has established a firm metabolic link between PG enzymatic activity and thylakoid disassembly during chloroplast senescence and nitrogen starvation.