Levels of Lycopene β-Cyclase 1 Modulate Carotenoid Gene Expression and Accumulation in Daucus carota

Abstract

Plant carotenoids are synthesized and accumulated in plastids through a highly regulated pathway. Lycopene β-cyclase (LCYB) is a key enzyme involved directly in the synthesis of α-carotene and β-carotene through the cyclization of lycopene. Carotenoids are produced in both carrot (Daucus carota) leaves and reserve roots, and high amounts of α-carotene and β-carotene accumulate in the latter. In some plant models, the presence of different isoforms of carotenogenic genes is associated with an organ-specific function. D. carota harbors two Lcyb genes, of which DcLcyb1 is expressed in leaves and storage roots during carrot development, correlating with an increase in carotenoid levels. In this work, we show that DcLCYB1 is localized in the plastid and that it is a functional enzyme, as demonstrated by heterologous complementation in Escherichia coli and over expression and post transcriptional gene silencing in carrot. Transgenic plants with higher or reduced levels of DcLcyb1 had incremented or reduced levels of chlorophyll, total carotenoids and β-carotene in leaves and in the storage roots, respectively. In addition, changes in the expression of DcLcyb1 are accompanied by a modulation in the expression of key endogenous carotenogenic genes. Our results indicate that DcLcyb1 does not possess an organ specific function and modulate carotenoid gene expression and accumulation in carrot leaves and storage roots.

A kiwifruit (Actinidia deliciosa) R2R3‐MYB transcription factor modulates chlorophyll and carotenoid accumulation

“…Inhibition of PSY or PDS activity affects carotenoid content and results in a bleached phenotype due to the virtual absence of carotenoid compounds (Fray & Grierson, 1993;McCarthy et al, 2004;Qin et al, 2007). It has also been shown that overexpression of LCY-b in transgenic carrot lines results in the increased expression of PSY genes, suggesting a positive feedback effect controlling the carotenoid pathway (Moreno et al, 2013). Consistent with the increased expression of the carotenoid genes in the transgenic N. benthamiana plants, the transcriptomic analysis of AdMYB7infiltrated N. benthamiana leaves showed the upregulation of NbGGPPS, NbPSY, NbPDS, NbCRTISO and NbLCY-b.…”

Comparative analysis of plant lycopene cyclases

“…b-LCY alone produces b-carotene whereas two enzymes, b-LCY and e-LCY (EC: 5.5.1.18), together form a-carotene (Beyer et al, 1991;Hornero-Méndez and Britton, 2002;Moreno et al, 2013). b-LCYs of plants and bacteria have a conserved dinucleotide binding motif. Furthermore, several conserved domains such as conserved region b-LCY's, b-LCY specific motif, cylase motif I and II (CMI and CMII), b-LCY CAD (catalytic activity domain) and a charged region are highly conserved in plants ( Moreno et al, 2013;Hugueney et al, 1995). b-LCY CAD is essential for b-LCY activity (Moreno et al, 2013).…”

“…Furthermore, several conserved domains such as conserved region b-LCY's, b-LCY specific motif, cylase motif I and II (CMI and CMII), b-LCY CAD (catalytic activity domain) and a charged region are highly conserved in plants ( Moreno et al, 2013;Hugueney et al, 1995). b-LCY CAD is essential for b-LCY activity (Moreno et al, 2013). Cyclization of lycopene is formed by LYCs and conserved in various organisms (Armstrong et al, 1990).…”

Carotenoids in Carrot

“…It is therefore conceivable that isoforms PSY1, ZDS1, and LCYB2 are mainly responsible for the production of carotenoids for photosynthesis and photoprotection (chloroplasts) whereas PSY2, ZDS2, and LCYB1 would be most involved in the biosynthesis of carotenoid in dark-grown carrot roots (chromoplasts). Recent work confirmed the involvement of LCYB1 in carotenoid biosynthesis in storage roots but also in leaves [44]. Further work will be required to define the specific role of all enzyme isoforms in carrot.…”