Identification of genes involved in shea butter biosynthesis from Vitellaria paradoxa fruits through transcriptomics and functional heterologous expression

Yongjun Wei,Boyang Ji,Jens Nielsen,Verena Siewers,Barbara Ann Halkier,Deyang Xu

doi:10.1007/s00253-019-09720-3

Abstract

Shea tree (Vitellaria paradoxa) is one economically important plant species that mainly distributes in West Africa. Shea butter extracted from shea fruit kernels can be used as valuable products in the food and cosmetic industries. The most valuable composition in shea butter was one kind of triacylglycerol (TAG), 1,3-distearoyl-2-oleoyl-glycerol (SOS, C18:0–C18:1–C18:0). However, shea butter production is limited and little is known about the genetic information of shea tree. In this study, we tried to reveal genetic information of shea tree and identified shea TAG biosynthetic genes for future shea butter production in yeast cell factories. First, we measured lipid content, lipid composition, and TAG composition of seven shea fruits at different ripe stages. Then, we performed transcriptome analysis on two shea fruits containing obviously different levels of SOS and revealed a list of TAG biosynthetic genes potentially involved in TAG biosynthesis. In total, 4 glycerol-3-phosphate acyltransferase (GPAT) genes, 8 lysophospholipid acyltransferase (LPAT) genes, and 11 diacylglycerol acyltransferase (DGAT) genes in TAG biosynthetic pathway were predicted from the assembled transcriptome and 14 of them were cloned from shea fruit cDNA. Furthermore, the heterologous expression of these 14 potential GPAT, LPAT, and DGAT genes in Saccharomyces cerevisiae changed yeast fatty acid and lipid profiles, suggesting that they functioned in S. cerevisiae. Moreover, two shea DGAT genes, VpDGAT1 and VpDGAT7, were identified as functional DGATs in shea tree, showing they might be useful for shea butter (SOS) production in yeast cell factories.

Highlights

Shea butter is a valuable product in the cosmetic industry; it can be used as a cocoa butter substitute (CBS) in the chocolate industry (Jahurul et al 2013)
By cloning and characterizing TAG biosynthetic genes of glycerol-3-phosphate acyltransferase (GPAT), lysophospholipid acyltransferase (LPAT), and diacylglycerol acyltransferase (DGAT) in shea fruit, we identified several functional TAG biosynthetic genes
Relative fatty acid amounts of these seven fruits were different, such as C18:0 fatty acid in the TAGs increased from T5 to T7, while some fatty acids decreased from T3 to T7, showing that the fatty acid production profiles of the TAGs were different in these shea fruits (Figure S2)

Summary

Introduction

Shea butter is a valuable product in the cosmetic industry; it can be used as a cocoa butter substitute (CBS) in the chocolate industry (Jahurul et al 2013). Shea butter was extracted from the kernels of shea tree (Vitellaria paradoxa) fruits (Davrieux et al 2010; Jahurul et al 2013). It represents 40–55% of the dry weight of the ripe shea tree fruits (Davrieux et al 2010). Developing other strategies, such as microbial cell factories, for CB (SOS) production is of interest (Clough et al 2009; Wei et al 2018)

Methods

Results

Conclusion