Enhancing the carotenoid content of Brassica napus seeds by downregulating lycopene epsilon cyclase

Abstract

The accumulation of carotenoids in higher plants is regulated by the environment, tissue type and developmental stage. In Brassica napus leaves, beta-carotene and lutein were the main carotenoids present while petals primarily accumulated lutein and violaxanthin. Carotenoid accumulation in seeds was developmentally regulated with the highest levels detected at 35-40 days post anthesis. The carotenoid biosynthesis pathway branches after the formation of lycopene. One branch forms carotenoids with two beta rings such as beta-carotene, zeaxanthin and violaxanthin, while the other introduces both beta- and epsilon-rings in lycopene to form alpha-carotene and lutein. By reducing the expression of lycopene epsilon-cyclase (epsilon-CYC) using RNAi, we investigated altering carotenoid accumulation in seeds of B. napus. Transgenic seeds expressing this construct had increased levels of beta-carotene, zeaxanthin, violaxanthin and, unexpectedly, lutein. The higher total carotenoid content resulting from reduction of epsilon-CYC expression in seeds suggests that this gene is a rate-limiting step in the carotenoid biosynthesis pathway. epsilon-CYC activity and carotenoid production may also be related to fatty acid biosynthesis in seeds as transgenic seeds showed an overall decrease in total fatty acid content and minor changes in the proportions of various fatty acids.

Carotenoids in nature: insights from plants and beyond

“…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. 1) (Yu et al 2008;Bai et al 2009). Investigations have yielded mutants perturbing lutein biosynthesis including lut1, e-hydroxylase (Tian et al 2004); lut2, eLCY (Cunningham et al 1996;Pogson et al 1996); ccr2, CRTISO (Park et al 2002); and lut5, an additional b-hydroxylase (Kim and DellaPenna 2006) as well as the SDG8 chromatin regulatory mutant, ccr1 (Cazzonelli et al 2009a).…”

“…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). However, another report showed that tuber specific silencing of eLCY resulted in an expected increase in b-carotene levels in potato (Solanum tuberosum) (Diretto et al 2006).…”

Biochemical and molecular characterization of orange- and tangerine-colored rice calli

“…The embryos of maize lcyB mutant have been shown to accumulate lycopene and δ-carotene, whereas the endosperm accumulates lycopene, δ-carotene, γ-carotene, and ε-carotene (Bai et al 2009); however, these carotenoids are almost absent in the wild type. The suppression of ε LCY expression by RNAi techniques in Brassica napus resulted in the increase of carotenoids and in the ratio of β-carotene to lutein (Yu et al 2008). In potato, tuber-specific silencing of ε LCY gene by introducing an antisense fragment of the gene caused an increase in β-carotene and zeaxanthin, although not in lutein (Diretto et al 2006).…”

“…In the absence of β LCY, several unusual carotenes have been shown to accumulate in maize (Zea mays L.; Bai et al 2009). The suppression of ε LCY expression results in an increase in carotenoid content and the ratio of β-carotene to lutein in Brassica napus seed (Yu et al 2008). On the other hand, tuber-specific silencing of the ε LCY gene, by introducing an antisense fragment of the gene, increases β-carotene and zeaxanthin contents in potato tuber (Solanum tuberosum L.; Diretto et al 2006).…”

Presence of Two Variants of Lycopene β-Cyclase Gene in Genomes of Citrus and its Relatives

“…Genes encoding lycopene β-cyclase (LCYb) and lycopene ε-cyclase (LCYe) are involved in the biosynthesis of β-carotene and α-carotene (9,10,27). Downregulation of LCYb leads to the accumulation of lycopene in ripe tomato fruits (19).…”