Subchromoplast Sequestration of Carotenoids Affects Regulatory Mechanisms in Tomato Lines Expressing Different Carotenoid Gene Combinations

Abstract

Metabolic engineering of the carotenoid pathway in recent years has successfully enhanced the carotenoid contents of crop plants. It is now clear that only increasing biosynthesis is restrictive, as mechanisms to sequestrate these increased levels in the cell or organelle should be exploited. In this study, biosynthetic pathway genes were overexpressed in tomato (Solanum lycopersicum) lines and the effects on carotenoid formation and sequestration revealed. The bacterial Crt carotenogenic genes, independently or in combination, and their zygosity affect the production of carotenoids. Transcription of the pathway genes was perturbed, whereby the tissue specificity of transcripts was altered. Changes in the steady state levels of metabolites in unrelated sectors of metabolism were found. Of particular interest was a concurrent increase of the plastid-localized lipid monogalactodiacylglycerol with carotenoids along with membranous subcellular structures. The carotenoids, proteins, and lipids in the subchromoplast fractions of the transgenic tomato fruit with increased carotenoid content suggest that cellular structures can adapt to facilitate the sequestration of the newly formed products. Moreover, phytoene, the precursor of the pathway, was identified in the plastoglobule, whereas the biosynthetic enzymes were in the membranes. The implications of these findings with respect to novel pathway regulation mechanisms are discussed.

Carotenogenesis Is Regulated by 5′UTR-Mediated Translation of Phytoene Synthase Splice Variants

“…This indicates that there are additional mechanisms capable of compensating flux overflow; the feedback control of carotenoid synthesis would represent the most sustainable solution. In nongreen tissues, the relevance of feedback-controlled AtPSY translation may be in the prevention of carotenoid accumulation in the form of microcrystals, which are thought to be largely inaccessible by CCDs and thus exempt from homeostatic control (Maass et al, 2009;Nogueira et al, 2013).…”

“…Moreover, PSY protein levels were recently found to be posttranslationally regulated by the ORANGE proteins in Arabidopsis (Zhou et al, 2015). Additionally, potential feedbackregulatory mechanisms involve translation, plastid import, protein-protein interaction, and protein turnover to achieve stoichiometrically defined carotenoid biosynthetic complexes (Cazzonelli and Pogson, 2010;Nogueira et al, 2013;Arango et al, 2014;Avendaño-Vázquez et al, 2014;Tian, 2015).…”

A Comprehensive Analysis of Chromoplast Differentiation Reveals Complex Protein Changes Associated with Plastoglobule Biogenesis and Remodeling of Protein Systems in Sweet Orange Flesh

“…Chromoplasts exhibit various morphologies, such as crystalline, globular, tubular, and membranous structures (Egea et al, 2010). The relationship between the architecture and carotenoid composition has been well stated in diverse pepper (Capsicum annuum) and tomato (Solanum lycopersicum) fruits (Kilcrease et al, 2013;Nogueira et al, 2013). Crystalline bodies have been observed in carrot (Daucus carota;Frey-Wyssling and Schwegler, 1965) and tomato (Harris and Spurr, 1969), which predominantly consist of b-carotene and lycopene, respectively.…”

Engineering of tomato for the sustainable production of ketocarotenoids and its evaluation in aquaculture feed

“…Carotenoids were extracted from freeze-dried tomatoes, freezedried trout parts (fillets, livers, and eyes), feces, and feeds. Extractions and analyses were carried out following a protocol previously published (37). A detailed description is shown in SI Appendix, SI Text.…”