Regulation and activation of phytoene synthase, a key enzyme in carotenoid biosynthesis, during photomorphogenesis

Abstract

During photomorphogenesis in higher plants, a coordinated increase occurs in the chlorophyll and carotenoid contents. The carotenoid level is under phytochrome control, as reflected by the light regulation of the mRNA level of phytoene synthase (PSY), the first enzyme in the carotenoid biosynthetic pathway. We investigated PSY protein levels, enzymatic activity and topological localization during photomorphogenesis. The results revealed that PSY protein levels and enzymatic activity increase during de-etiolation and that the enzyme is localized at thylakoid membranes in mature chloroplasts. However, under certain light conditions (e.g., far-red light) the increases in PSY mRNA and protein levels are not accompanied by an increase in enzymatic activity. Under those conditions, PSY is localized in the prolamellar body fraction in a mostly enzymatically inactive form. Subsequent illumination of dark-grown and/or in far-red light grown seedlings with white light causes the decay of these structures and a topological relocalization of PSY to developing thylakolds which results in its enzymatic activation. This light-dependent mechanism of enzymatic activation of PSY in carotenoid biosynthesis shares common features with the regulation of the NADPH:protochlorophyllide oxidoreductase, the first light-regulated enzyme in chlorophyll biosynthesis. The mechanism of regulation described here may contribute to ensuring a spatially and temporally coordinated increase in both carotenoid and chlorophyll contents.

The Maize Phytoene Synthase Gene Family: Overlapping Roles for Carotenogenesis in Endosperm, Photomorphogenesis, and Thermal Stress Tolerance

“…Early in endosperm development (10 DAP) and in unfertilized ovule tissue, transcripts were present, but no PSY1 antigen was detected. Even though transcript levels were about the same between 10 and 12 DAP, PSY protein was first detected at 12 DAP, suggesting that PSY accumulation might be linked to endosperm development and plastid biogenesis, as previously observed for posttranscriptional regulation of PSY destined for chloroplasts (Welsch et al, 2000). The period of 14 to 16 DAP also showed the steepest rise in accumulated carotenoids for a given time frame, following induction of PSY protein seen between 10 and 12 DAP.…”

“…Chloroplast envelope membranes were shown to contain a unique carotenoid profile compared to thylakoid membranes (Jeffrey et al, 1974;Siefermann-Harms et al, 1978); chloroplast envelope membrane extracts also exhibited enzyme activity for conversion of zeaxanthin to violaxanthin (Costes et al, 1979). More recent reports have localized PSY and other pathway enzymes to thylakoid membranes in chloroplasts (Linden et al, 1993;Bonk et al, 1997;Welsch et al, 2000). Therefore, the carotenoid pathway may actually be two pathways from a topological standpoint, potentially existing on envelope and thylakoid membranes.…”

Provitamin A Accumulation in Cassava (Manihot esculenta) Roots Driven by a Single Nucleotide Polymorphism in a Phytoene Synthase Gene

“…The ORF of Sinapis alba GGPS, with its putative transit peptide truncated as indicated by Welsch et al (2000), was cloned in vivo in the vector pNXgate using the yeast strain THY.AP5. The resulting vector pNubGGPSdTP encoded GGPS as a translational fusion with an N-terminal HA tag.…”

“…pET-GGPS contained the S. alba GGPS ORF, with its putative transit peptide truncated. It was obtained by subcloning a BamHI/SalI fragment from pGGPS (Welsch et al, 2000) into the accordingly digested vector pETDuet-1. For pCDF-CrtI, the CrtI ORF was amplified from pBaal2 (Ye et al, 2000) with the primers CrtIEco and CrtIHind, the PCR fragment digested with EcoRI and HindIII and subcloned into the accordingly digested vector pCDFDuet-1.…”

Direct regulation of phytoene synthase gene expression and carotenoid biosynthesis by phytochrome-interacting factors

“…Nonetheless, it is known that a major driving force for carotenoid production in different plant species is the transcriptional regulation of genes encoding phytoene synthase (PSY), the first and main rate-determining enzyme of the pathway (5,9,(11)(12)(13)(14). Consistently, the burst in carotenoid biosynthesis that occurs during deetiolation of Arabidopsis thaliana seedlings is correlated with a very fast up-regulation of PSY transcripts (15,16) and a concomitant increase in PSY protein levels and enzyme activity (17). This up-regulation of PSY gene expression is mediated by the phytochrome family of photoreceptors under red (R) and far-red (FR) light (12,13,16,18).…”