Abstract
BackgroundLycopene β-cyclase (LCYB) is a key enzyme catalyzing the biosynthesis of β-carotene, the main source of provitamin A. However, there is no documented research about this key cyclase gene’s function and relationship with β-carotene content in wheat. Therefore, the objectives of this study were to clone TaLCYB and characterize its function and relationship with β-carotene biosynthesis in wheat grains. We also aimed to obtain more information about the endogenous carotenoid biosynthetic pathway and thus provide experimental support for carotenoid metabolic engineering in wheat.ResultsIn the present study, a lycopene β-cyclase gene, designated TaLCYB, was cloned from the hexaploid wheat cultivar Chinese Spring. The cyclization activity of the encoded protein was demonstrated by heterologous complementation analysis. The TaLCYB gene was expressed differentially in different tissues of wheat. Although TaLCYB had a higher expression level in the later stages of grain development, the β-carotene content still showed a decreasing tendency. The expression of TaLCYB in leaves was dramatically induced by strong light and the β-carotene content variation corresponded with changes of TaLCYB expression. A post-transcriptional gene silencing strategy was used to down-regulate the expression of TaLCYB in transgenic wheat, resulting in a decrease in the content of β-carotene and lutein, accompanied by the accumulation of lycopene to partly compensate for the total carotenoid content. In addition, changes in TaLCYB expression also affected the expression of several endogenous carotenogenic genes to varying degrees.ConclusionOur results suggest that TaLCYB is a genuine lycopene cyclase gene and plays a crucial role in β-carotene biosynthesis in wheat. Our attempt to silence it not only contributes to elucidating the mechanism of carotenoid accumulation in wheat but may also help in breeding wheat varieties with high provitamin A content through RNA interference (RNAi) to block specific carotenogenic genes in the wheat endosperm.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0514-5) contains supplementary material, which is available to authorized users.
Highlights
Lycopene β-cyclase (LCYB) is a key enzyme catalyzing the biosynthesis of β-carotene, the main source of provitamin A
These results suggested that TaLCYB isolated from wheat was a genuine member of the plant lycopene β-cyclase family
Extracts from pAC-LYC + pET32-LCYB cells mainly accumulated β-carotene, the cultures turned yellow with an undefined peak, and lycopene was virtually undetectable. These results demonstrated that TaLCYB was a functional β-cyclase in the carotenoid biosynthetic pathway in E. coli, which could convert lycopene to β-carotene
Summary
Lycopene β-cyclase (LCYB) is a key enzyme catalyzing the biosynthesis of β-carotene, the main source of provitamin A. There is no documented research about this key cyclase gene’s function and relationship with β-carotene content in wheat. Carotenoids are important natural isoprenoid pigments synthesized in plants that have essential roles in protecting against excess light energy and oxidative damage, and in light-harvesting [1,2]. Their provitamin A activity and antioxidant properties are their most attractive functions. Lycopene is cyclized by LCYE and LCYB to introduce ε and β-ionone end groups and produce α- and β-carotene, Zeng et al BMC Plant Biology (2015) 15:112 respectively (Figure 1). Plant LCYBs share similar and highly conserved functional domains, which are involved in many reactions in β-ionone catalysis [10,14]
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