Plastoglobules: versatile lipoprotein particles in plastids

Abstract

Plastoglobules are plastid-localized lipoprotein particles that contain tocopherols and other lipid isoprenoidderived metabolites, as well as structural proteins named plastoglobulins. Surprisingly, recent publications show that plastoglobules contain enzymes involved in the metabolism of these secondary metabolites, as well as enzymes of unknown function. The size and number of plastoglobules vary during plastid development and differentiation, and strongly increase during light stress, senescence and in mutants blocked in thylakoid formation. Given that plastoglobules are contiguous with the outer lipid leaflet of the thylakoid membrane, it is highly plausible that a function of plastoglobules is the active channeling of lipid molecules and lipid breakdown products. Understanding the function of plastoglobules should provide a foundation for improving the nutritional value and yield of plants.History of plastoglobule research and discovery Early electron microscopic studies revealed the presence of 'osmiophilic globuli' inside chloroplasts ( Figure 1) and chromoplasts, as well as other plastid types [1]. The diameter of these bodies, later termed plastoglobules, ranges from 30 nm to 5 mm. These plastoglobules could be conveniently isolated by flotation density centrifugation because of their relatively high lipid content [1,2]. The lipid composition of plastoglobules has been determined in several plant species -it consists mainly of prenyl-quinones and neutral lipids. Plastoglobules qualify as lipoprotein particles because they have been reported to associate with proteins. Members of the plastoglobulin family (also called fibrillin or PAP for plastid lipid-associated protein) [3], were the first known genuine plastoglobule protein components. In addition to vascular plants, plastoglobules are found in non-vascular species such as moss [4] and algae [5,6]. Interestingly, carotenoid-rich plastoglobule-like structures constitute the eyespot structure of Chlamydomonas reinhardtii, the proteome of which has been shown to contain members of the plastoglobulin family [6]. In cyanobacteria, the presence of 'lipid droplets' among the thylakoids has been reported [7]. The exact identity of these lipid droplets has not been defined; however, the presence of at least two plastoglobulin homologs in the genome of Synechocystis PCC6803 suggests that they could be plastoglobules.Although plastoglobules were largely viewed as passive lipid and carotenoid storage particles, their varying size in different species, plastid types and developmental stages suggested a more dynamic role. Moreover, correlative evidence suggested that plastoglobules are involved in thylakoid development as well as disassembly: (i) etioplasts with poorly developed thylakoids have more plastoglobules than are found in chloroplasts, but the plastoglobule abundance decreased during thylakoid biogenesis [8-10]; (ii) in senescent chloroplasts, during thylakoid disassembly, plastoglobules enlarge and accumulate [9,11,12]; (iii) several thylakoid biogenesis...

Knocking Down of Isoprene Emission Modifies the Lipid Matrix of Thylakoid Membranes and Influences the Chloroplast Ultrastructure in Poplar

“…Plastoglobules are lipoprotein particles containing isoprenoid-driven metabolites (primarily prenylquinones, including plastoquinone and phylloquinone), tocopherols , and structural proteins (plastoglobulins; Bréhélin et al, 2007). The increased number of plastoglobules in NE compared with IE chloroplasts might reflect the higher levels of a-tocopherol in leaves of these lines, as demonstrated previously (Behnke et al, 2010b). )…”

“…Moreover, plastoglobules are involved in different secondary metabolism pathways, stress responses, and the development of thylakoids (Bréhélin et al, 2007). In a previous study, we showed that the lipid-associated protein fibrillin content, comprising lipid-associated proteins and fibrillins, is negatively correlated with the NE plants (Velikova et al, 2014).…”

Update on the biochemistry of chlorophyll breakdown

“…At5g17450 was identified to be coexpressed, together with PPH and PAO, with proteins that localize to plastoglobules (Lundquist et al 2012). Plastoglobules are thylakoid-associated lipoprotein particles that are suggested to have an important role in lipid metabolism during different developmental phases, but particularly during senescence (Bréhélin et al 2007). …”

Modified Clp Protease Complex in the ClpP3 Null Mutant and Consequences for Chloroplast Development and Function in Arabidopsis

“…PGs are thylakoid-associated lipoprotein particles that serve as compartments for the synthesis, storage, and degradation of prenyl lipids and thylakoid membrane remodeling (Bréhélin et al, 2007;Lundquist et al, 2012). The total mass of PG proteins increased 2.6-fold (Supplemental Table S4).…”