Carotenoid analysis of sweetpotatoIpomoea batatasand functional identification of its lycopene β- and ε-cyclase genes

Abstract

Abstract:Sweetpotato Ipomoea batatas 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 IbLCYb1, 2, and from W71, IbLCYb3, 4, 5. Meanwhile, only a single lycopene ε-cyclase gene sequence, designated IbLCYe, was isolated from both WS and W71. These genes were separately introduced into a lycopene-synthesizing Escherichia coli transformed with the Pantoea ananatis crtE, crtB and crtI genes, followed by HPLC analysis. β-Carotene was detected in E. coli cells that carried IbLCYb1-4, indicating that the IbLCYb1-4 genes encode lycopene β-cyclase. Meanwhile, the introduction of IbLCYe into the lycopene-synthesizing E. coli led to efficient production of δ-carotene with a monocyclic ε-ring, providing evidence that the IbLCYe gene codes for lycopene ε-(mono)cyclase. Expression of the β-and ε-cyclase genes was analyzed as well.Keywords: α-carotene; β-carotene; carotenoid; Ipomoea batatas; lycopene cyclase; sweetpotato.Dedication: This work is dedicated to the memory of Professor Peter BÖger. He kindly provided the opportunity for NM to work in his laboratory on the generation of bleaching herbicide-resistant plants, and encouraged NM to work on carotenoid biosynthesis.

Comparative transcriptome analysis implied a ZEP paralog was a key gene involved in carotenoid accumulation in yellow-fleshed sweetpotato

“…Additionally, zeaxanthin was accumulated in potato tubers by suppressing ZEP expression, and the tubers showed a slightly deeper yellow colour 31 . Unique carotenoids in sweetpotato such as β-carotene 5,8;5′,8′-diepoxide and β-cryptoxanthin 5,8-epoxide are also synthesised by β-ring epoxidation of β-carotene and β-cryptoxanthin 7 , 9 . It was predicted that this epoxidation was regulated by a novel enzyme encoded by the ZEP paralog 7 .…”

“…Unique carotenoids in sweetpotato such as β-carotene 5,8;5′,8′-diepoxide and β-cryptoxanthin 5,8-epoxide are also synthesised by β-ring epoxidation of β-carotene and β-cryptoxanthin 7 , 9 . It was predicted that this epoxidation was regulated by a novel enzyme encoded by the ZEP paralog 7 . However, no such ZEP paralog has yet been identified in sweetpotato.…”

“…These pigments cause a yellow colour in storage roots. Figure 1 shows a proposed biosynthetic pathway of carotenoids in sweetpotato 7 – 9 . A lot of genes regulate the biosynthesis of carotenoids.…”

“…On the other hand, β-cryptoxanthin epoxides and β-carotene epoxides in yellow-fleshed sweetpotato are generated by the epoxidation of β-rings in β-cryptoxanthin and β-carotene, respectively. Khan et al (2016) 7 suggest that these epoxidation steps may be catalysed by a novel enzyme highly homologous to ZEP. However, ZEP paralogs encoding such an enzyme have not yet been identified in sweetpotato.…”

A Greener HPTLC Approach for the Determination of β-Carotene in Traditional and Ultrasound-Based Extracts of Different Fractions of Daucus carota (L.), Ipomea batatas (L.), and Commercial Formulation

“…Dietary fiber, carbohydrates, vitamin A (as β-carotene), vitamin B6, vitamin C, copper, manganese, potassium, and iron are all found in the root of I. batatas [12]. Sweet potato also had some other carotenoids, including β-carotene-5,8,5 ,8 -diepoxide, β-carotene-5,8-epoxide, and ipomoeaxanthin A, in addition to β-carotene [13]. Furthermore, it had great potential for bioenergy production [12,13].…”