Regulation of lutein biosynthesis and prolamellar body formation in Arabidopsis

Abstract

Abstract. Carotenoids are critical for photosynthetic function in chloroplasts, and are essential for the formation of the prolamellar body in the etioplasts of dark-grown (etiolated) seedlings. They are also precursors for plant hormones in both types of plastids. Lutein is one of the most abundant carotenoids found in both plastids. In this study we examine the regulation of lutein biosynthesis and investigate the effect of perturbing carotenoid biosynthesis on the formation of the lattice-like membranous structure of etioplasts, the prolamellar body (PLB). Analysis of mRNA abundance in wildtype and lutein-deficient mutants, lut2 and ccr2, in response to light transitions and herbicide treatments demonstrated that the mRNA abundance of the carotenoid isomerase (CRTISO) and epsilon-cyclase (εLCY) can be rate limiting steps in lutein biosynthesis. We show that accumulation of tetra-cis-lycopene and all-trans-lycopene correlates with the abundance of mRNA of several carotenoid biosynthetic genes. Herbicide treatments that inhibit carotenoid biosynthetic enzymes in wildtype and ccr2 etiolated seedlings were used to demonstrate that the loss of the PLB in ccr2 mutants is a result of perturbations in carotenoid accumulation, not indirect secondary effects, as PLB formation could be restored in ccr2 mutants treated with norflurazon.

Carotenoids in nature: insights from plants and beyond

“…Investigations have indicated that both CRITSO (ccr2) and SDG8 (ccr1) mutants have an inhibitory effect on eLCY transcript levels (Fig. 3), revealing that feedback may partially explain the reduced lutein observed in ccr2 and ccr1 mutants (Cuttriss et al 2007;Cazzonelli et al 2009a). Further, a reduction in seed eLCY mRNA levels show higher total carotenoid content, specifically increased levels of b-carotene, zeaxanthin, violaxanthin and unexpectedly, lutein (Yu et al 2008).…”

“…The control of carotenoid flux through the branch from alltrans-lycopene to synthesis of a-and b-carotenes is also under negative metabolite feedback regulation and mediated through the transcription control of eLCY gene expression (Cuttriss et al 2007). Investigations have indicated that both CRITSO (ccr2) and SDG8 (ccr1) mutants have an inhibitory effect on eLCY transcript levels (Fig.…”

“…2). Regulation by eLCY is the first committed step coordinating carotenoid flux through the b-e branch and modulates the ratio of the most abundant carotenoid, lutein to the b-carotenoids leading to changes in lutein content (Cuttriss et al 2007;Harjes et al 2008;Cazzonelli et al 2009a;Howitt et al 2009). A molecular synergism between eLCY and bLCY activities is an overall major determinant of flux through the branch leading to production of lutein, b-carotene and other xanthophylls cycle (XC) carotenoids ( Fig.…”

“…The regulation of carotenoid targeting, storage and sequestration within various plastid types is a process by which to modulate a sink for carotenoid accumulation (Lu et al 2006;Cuttriss et al 2007;. For example, the high-pigment 1 tomato mutant, hp1, displays an increased pigmentation because of increased chromoplast compartment size (Cookson et al 2003).…”

“…Several genes encoding enzymes in isoprenoid and carotenoid biosynthesis are the subject of negative and positive feedback regulatory processes and are likely to be mediated by a carotenoid or a molecule derived from a carotenoid (Römer et al 2000;Beyer et al 2002;Cuttriss et al 2007;Qin et al 2007;Bai et al 2009). There is strong evidence to show carotenoid metabolite feedback regulation requires post-transcriptional and transcriptional processes to modulate target genes that (1) supply isoprenoid precursors for carotenogenesis, (2) control activity of the ratelimiting phytoene synthase step and (3) control carotenoid flux through the branch to synthesis of a-and b-carotenes.…”