Carotenoid analysis of sweetpotato<i>Ipomoea batatas</i>and functional identification of its lycopene β- and ε-cyclase genes

<jats:title>Abstract</jats:title><jats:p>Sweetpotato<jats:italic>Ipomoea batatas</jats:italic>is known as a hexaploid species. Here, we analyzed carotenoids contained in the leaves and tubers of sweetpotato cultivars ‘White Star’ (WS) and W71. These cultivars were found to contain several carotenoids unique to sweetpotato tubers such as β-carotene-5,6,5′,8′-diepoxide and β-carotene-5,8-epoxide. Next, we isolated two kinds of carotene cyclase genes that encode lycopene β- and ε-cyclases from the WS and W71 leaves, by RT-PCR and subsequent RACE. Two and three lycopene β-cyclase gene sequences were, respectively, isolated from WS, named<jats:italic>IbLCYb1</jats:italic>,<jats:italic>2</jats:italic>, and from W71,<jats:italic>IbLCYb3</jats:italic>,<jats:italic>4</jats:italic>,<jats:italic>5</jats:italic>. Meanwhile, only a single lycopene ε-cyclase gene sequence, designated<jats:italic>IbLCYe</jats:italic>, was isolated from both WS and W71. These genes were separately introduced into a lycopene-synthesizing<jats:italic>Escherichia coli</jats:italic>transformed with the<jats:italic>Pantoea ananatis crtE</jats:italic>,<jats:italic>crtB</jats:italic>and<jats:italic>crtI</jats:italic>genes, followed by HPLC analysis. β-Carotene was detected in<jats:italic>E. coli</jats:italic>cells that carried<jats:italic>IbLCYb1</jats:italic>-<jats:italic>4</jats:italic>, indicating that the<jats:italic>IbLCYb1</jats:italic>-<jats:italic>4</jats:italic>genes encode lycopene β-cyclase. Meanwhile, the introduction of<jats:italic>IbLCYe</jats:italic>into the lycopene-synthesizing<jats:italic>E. coli</jats:italic>led to efficient production of δ-carotene with a monocyclic ε-ring, providing evidence that the<jats:italic>IbLCYe</jats:italic>gene codes for lycopene ε-(mono)cyclase. Expression of the β- and ε-cyclase genes was analyzed as well.</jats:p>