Chromoplast plastoglobules recruit the carotenoid biosynthetic pathway and contribute to carotenoid accumulation during tomato fruit maturation

Abstract

Tomato (Solanum lycopersicum) fruit maturation is associated with a developmental transition from chloroplasts (in mature green fruit) to chromoplasts (in red fruit). The hallmark red color of ripe tomatoes is due to carotenogenesis and accumulation of the red carotenoid lycopene inside chromoplasts. Plastoglobules (PG) are lipid droplets in plastids that are involved in diverse lipid metabolic pathways. In tomato, information on the possible role of PG in carotogenesis and the PG proteome is largely lacking. Here, we outline the role of PG in carotenogenesis giving particular attention to tomato fruit PG proteomes and metabolomes. The proteome analysis revealed the presence of PG-typical FBNs, ABC1K-like kinases, and metabolic enzymes, and those were decreased in the PG of tomato chromoplasts compared to chloroplasts. Notably, the complete β-carotene biosynthesis pathway was recruited to chromoplast PG, and the enzymes PHYTOENE SYNTHASE 1 (PSY-1), PHYTOENE DESATURASE (PDS), ZETA-CAROTENE DESATURASE (ZDS), and CAROTENOID ISOMERASE (CRTISO) were enriched up to twelvefold compared to chloroplast PG. We profiled the carotenoid and prenyl lipid changes in PG during the chloroplast to chromoplast transition and demonstrated large increases of lycopene and β-carotene in chromoplast PG. The PG proteome and metabolome are subject to extensive remodeling resulting in high accumulation of lycopene during the chloroplast-to-chromoplast transition. Overall, the results indicate that PGs contribute to carotenoid accumulation during tomato fruit maturation and suggest that they do so by functioning as a biosynthetic platform for carotenogenesis.

Nutritional Enrichment of Plant Leaves by Combining Genes Promoting Tocopherol Biosynthesis and Storage

“…Notably, VTE2 and VTE3 protein localization in chromoplasts has not been confirmed yet, while they have been assigned to the inner envelope of chloroplasts. Changes in plastid ultrastructure and in enzyme localization could reduce either the access to precursors or the access to the downstream enzymes to the MPBQ and dMPBQ pools [ 25 , 26 ]. Furthermore, downstream genes such as VTE1 and VTE4 were found to be expressed at lower levels in leaves developing artificial chromoplasts compared to control leaf tissues harboring chloroplasts [ 10 ], so it is possible that a putatively higher supply of precursors due to VTE2 or VTE3 overexpression could not be efficiently converted into tocopherol end products.…”

“…VTE4 protein was reported to be localized at the inner envelope of chloroplasts but to have high accessibility to the γ-TC pool present in the PG [ 30 ]. Chromoplast PG could be more efficient in the recruitment of enzymes involved in tocopherol biosynthesis, facilitating the role of VTE4 in a similar fashion to what was observed for carotenoid biosynthesis [ 26 ]. The combination of VTE4 with p-crtB allows the production of leaf material with VitE amounts that are comparable to those found in soybeans [ 28 ].…”

“…The overexpression of VTE1 resulted in an increased amount of PC-8, as expected ( Figure 1 ). Conversion of PQ-9 to plastoquinol can happen in response to photooxidation and thylakoid degradation in plant leaves or tomato and pepper fruits [ 26 , 42 , 45 ]. Likely, a high basal level of available plastoquinol in crtB chromoplasts might provide the substrate for VTE1 function while the increased PG number provides the synthesis and storage space [ 9 , 10 ].…”

A quantitative method to measure geranylgeranyl diphosphate (GGPP) and geranylgeranyl monophosphate (GGP) in tomato (Solanum lycopersicum) fruit

“…In addition, GGPP as an essential biosynthetic precursor in plant tissues is rapidly converted by enzymes to downstream secondary metabolites, complicating its detection. For these reasons, in most studies, instead of directly analysing GGPP, researchers have measured its downstream products such as carotenoids, quinones or other derived terpenoids [5,6,10,11]. We are not aware of any reliable method able to measure GGPP physiological levels in plants, even though McCaskill et Croteau reported a complex and time-consuming procedure for the isolation and quanti cation of radiolabelled intermediates of the MVA pathway by ion-pairing chromatography coupled to radiodetection [12].…”

Chromoplast differentiation: a central role for plastoglobule lipid droplets comes into focus

“…The direct ontogenic relationship between plastoglobules and fibrils has been supported by extensive transmission electron microscopic and biochemical analyses of ripening pepper fruits (Berry et al ., 2019). Moreover, recent proteome profiling of plastoglobules during the natural transition of chloroplast to chromoplast in ripening tomato fruit demonstrated a recruitment of the carotenoid biosynthetic pathway onto plastoglobules, which would be expected to drive the accumulation of carotenoids and the transition of plastoglobules into carotenoid‐rich fibrils characteristic of fully developed chromoplasts (Zita et al ., 2022).…”