Heterologous expression of xanthophyll esterase genes affects carotenoid accumulation in petunia corollas

Sanae Kishimoto,Akemi Ohmiya,Chihiro Oda-Yamamizo

doi:10.1038/s41598-020-58313-y

Abstract

The majority of carotenoids in petals are xanthophylls and most of these xanthophylls are esterified with fatty acids. Although petunia (Petunia x hybrida) is an important ornamental plant, it cannot accumulate enough carotenoids to have deep-yellow flowers. Our previous study suggested that low esterification activity causes low carotenoid accumulation in petunia corollas. Here, we introduced xanthophyll esterase (XES) from the petals of Ipomoea obscura, tomato (Solanum lycopersicum), and marigold (Tagetes erecta) into a pale-yellow-flowered cultivar of petunia to see whether these affect carotenoid accumulation in petunia corollas. Carotenoid contents and the proportions of esterified xanthophylls were elevated in the corollas of XES-overexpressing (XES-OX) transformants. Expression analysis showed that the transcript levels of endogenous carotenoid biosynthetic genes, which included geranylgeranyl diphosphate synthase 2, ζ-carotene desaturase, and lycopene β-ring cyclase in corolla tubes were upregulated in XES-OX plants. In addition, we discovered a difference in the composition of esterified xanthophylls among XES-OX plants, which may be caused by differences in the substrate specificity of their respective XESs. We conclude that esterification is an important process for carotenoid accumulation and XES is a useful tool for the quantitative and qualitative control of carotenoid accumulation in petals.

Highlights

The majority of carotenoids in petals are xanthophylls and most of these xanthophylls are esterified with fatty acids
We demonstrated that overexpression of these xanthophyll esterase (XES) genes promoted the esterification of xanthophylls, development of carotenoid-lipoprotein sequestering substructures in chromoplasts, and overexpression of three endogenous carotenoid biosynthetic genes, resulting in an increase in total carotenoid content in the petunia corollas
We previously reported that trans-xanthophylls in petunia corollas have lower esterification percentages than cis-xanthophylls, which suggests that PhXES has low substrate specificity for trans-xanthophylls[26]

Summary

Introduction

The majority of carotenoids in petals are xanthophylls and most of these xanthophylls are esterified with fatty acids. We introduced xanthophyll esterase (XES) from the petals of Ipomoea obscura, tomato (Solanum lycopersicum), and marigold (Tagetes erecta) into a pale-yellow-flowered cultivar of petunia to see whether these affect carotenoid accumulation in petunia corollas. Judging from the analysis of biosynthetic and catabolic gene expressions, amounts of carotenoids in petals might be mainly determined by the balance of biosynthesis and degradation Another important factor that affects carotenoid accumulation in petals is xanthophyll esterification. We made transgenic petunia plants overexpressing XES from a yellow-flowered variety of Ipomoea obscura (L.) Ker Gawl., tomato, and marigold (Tagetes erecta L.) Petals of these plants had large amounts of esterified trans-xanthophylls with various compositions, suggesting that the introduced XESs had high esterification activity in respect of trans-xanthophylls and different substrate specificities[5,15,17]. We showed that substrate specificity of XES affected the carotenoid profiles in the corollas of the transgenic plants

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Discussion

Conclusion