Mediation of a GDSL Esterase/Lipase in Carotenoid Esterification in Tritordeum Suggests a Common Mechanism of Carotenoid Esterification in Triticeae Species.

María Dolores Requena-Ramírez,Cristina Rodríguez-Suárez,Sergio G. Atienza,Dámaso Hornero-Méndez

doi:10.3389/fpls.2020.592515

Abstract

Carotenoids are essential in human diet, so that the development of programs toward carotenoid enhancement has been promoted in several crops. The cereal tritordeum, the amphiploid derived from the cross between Hordeum chilense Roem. et Schulz. and durum wheat has a remarkable carotenoid content in the endosperm. Besides, a high proportion of these carotenoids are esterified with fatty acids. The identification of the gene(s) responsible for xanthophyll esterification would be useful for breeding as esterified carotenoids show an increased ability to accumulate within plant cells and have a higher stability during post-harvest storage. In this work, we analyzed five genes identified as candidates for coding the xanthophyll acyltransferase (XAT) enzyme responsible for lutein esterification in H. chilense genome. All these genes were expressed during grain development in tritordeum, but only HORCH7HG021460 was highly upregulated. Sequence analysis of HORCH7HG021460 revealed a G-to-T transversion, causing a Glycine to Cysteine substitution in the protein of H290 (the only accession not producing quantifiable amounts of lutein esters, hereinafter referred as zero-ester) of H. chilense compared to the esterifying genotypes. An allele-specific marker was designed for the SNP detection in the H. chilense diversity panel. From the 93 accessions, only H290 showed the T allele and the zero-ester phenotype. Furthermore, HORCH7HG021460 is the orthologue of XAT-7D, which encodes a XAT enzyme responsible for carotenoid esterification in wheat. Thus, HORCH7HG021460 (XAT-7Hch) is a strong candidate for lutein esterification in H. chilense and tritordeum, suggesting a common mechanism of carotenoid esterification in Triticeae species. The transference of XAT-7Hch to wheat may be useful for the enhancement of lutein esters in biofortification programs.

Highlights

Carotenoids pigments are responsible for many of the yellow, orange, and bright red colors of fruits, vegetables, and flowers
Hordeum chilense shows a good degree of collinearity with H. vulgare (Ávila et al, 2019a) and, with all the members of the Triticeae tribe (Mayer et al, 2011)
The position of H. chilense genes identified using candidate gene approaches in previous works is in agreement with their position in other Triticeae species (Atienza et al, 2007a; Gil-Humanes et al, 2009; Rodríguez-Suárez and Atienza, 2012; Alvarez et al, 2019; Rodríguez-Suárez et al, 2020)

Summary

Introduction

Carotenoids pigments are responsible for many of the yellow, orange, and bright red colors of fruits, vegetables, and flowers. They have essential roles in light-harvesting, protection against excess of light energy and oxidative damage (Britton, 2008). The consumption of carotenoid-rich foods has been associated with a lower risk of developing some diseases, including several types of cancer (Nishino et al, 2009). Lutein has been suggested to play an important role during neural system development in infant brains (Johnson, 2014). Lutein and zeaxanthin are concentrated in the eye macula, i.e., the central part of the retina (Johnson, 2014), and their consumption alleviates age macular degeneration (AMD; Krinsky et al, 2003)

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