Enhancing the carotenoid content of Brassica napus seeds by downregulating lycopene epsilon cyclase
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The accumulation of carotenoids in higher plants is regulated by the environment, tissue type and developmental stage. In Brassica napus leaves, β-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 β rings such as β-carotene, zeaxanthin and violaxanthin, while the other introduces both β- and ε-rings in lycopene to form α-carotene and lutein. By reducing the expression of lycopene ε-cyclase (ε-CYC) using RNAi, we investigated altering carotenoid accumulation in seeds of B. napus. Transgenic seeds expressing this construct had increased levels of β-carotene, zeaxanthin, violaxanthin and, unexpectedly, lutein. The higher total carotenoid content resulting from reduction of ε-CYC expression in seeds suggests that this gene is a rate-limiting step in the carotenoid biosynthesis pathway. ε-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.
KeywordsCarotenoids Lycopene ε-cyclase Brassica napus Seeds RNAi silencing
We are grateful to Mr. Delwin Epp for technical assistance with B. napus tissue culture and Dr. Branimir Gjetvaj for assistance with the microarray analysis. We thank Drs. Kevin Falk, Kevin Rozwadowski and Bhinu V.S. for critical reading of the manuscript, and for helpful suggestions. Funding for this project was provided by the Saskatchewan Agriculture Development Fund.
- Carpenter CD, Simon AE (1998) Preparation of RNA. In: Martinez-Zapater JM, Salinas J (eds) Methods in molecular biology, vol. 82. Arabidopsis protocols. Humana Press, Totowa, NJ, pp 85–89Google Scholar
- Cuttriss AJ, Pogson BJ (2004) Carotenoids. In: Davies KM (ed) Plant pigments and their manipulation. CRC Press, Boca Raton, FL, pp 57–91Google Scholar
- Goodwin TW (1980) The biochemistry of the carotenoids, 2nd edn., vol 1. Chapman & Hall, London, pp 377Google Scholar
- Kirk JT, Tiliney-Bassett RA (1978) Proplastids, etioplasts, amyloplasts, chromoplasts and other plastids. In: Kirck ST, Tiliney-Bassett RA (eds) The plastids:their chemistry, structure, growth and inheritance. Elsevier/North Holland, Biomedical Press, Amsterdam, pp 217–239Google Scholar
- Landrum JT, Bone RA (2004) Dietary lutein and zeaxanthin: reducing the risk of macular degeneration. Agro Food Industry Hi-Tech 15:22–25Google Scholar
- Li L, Van Eck J (2007) Metabolic engineering of carotenoid accumulation by creating a metabolic sink. Transgenic Res DOI 10.1007/s11248-007-9111-1Google Scholar
- Soeda Y, Konings MCJM, Vorst O, van Houwelingen AMML, Stoopen GM, Maliepaard CA, Kodde J, Bino RJ, Groot SPC, van der Geest AHM (2005) Gene expression programs during Brassica oleracea seed maturation, osmopriming, and germination are Indicators of progression of the germination process and the stress tolerance level. Plant Physiol 137:354–368PubMedCrossRefGoogle Scholar
- Young AJ (1993) Factors that affect the carotenoid composition of higher plants and algae. In: Young AJ, Britton G (eds) Carotenoids in photosynthesis. Chapman and Hall, London, pp 161–205Google Scholar
- Young LW, Jalink H, Denkert R, Reaney MTJ (2006) Factors affecting the density of Brassica napus seeds. Seed Sci & Technol 34:633–645Google Scholar