Fatty Acid and Associated Gene Expression Analyses of Three Tree Peony Species Reveal Key Genes for α-Linolenic Acid Synthesis in Seeds.

Qing-Yu Zhang,Rui Yu,Li-Xin Niu,Li-Hang Xie,Md Mahbubur Rahman,Yan-Long Zhang,Aruna Kilaru

doi:10.3389/fpls.2018.00106

Abstract

The increasing demand for healthy edible oil has generated the need to identify promising oil crops. Tree peony (Paeonia section Moutan DC.) is a woody oil crop with α-linolenic acid (ALA) contributing for 45% of the total fatty acid (FA) content in seeds. Molecular and genetic differences that contribute to varied FA content and composition among the wild peony species are, however, poorly understood. Analyses of FA content and composition during seed development in three tree peony species (Paeonia rockii, P. potaninii, and P. lutea) showed varied FA content among them with highest in P. rockii, followed by P. potaninii, and P. lutea. Total FA content among these species increased with seed development and reached its maximum in its final stage. Seed FA composition analysis of the three species also revealed that ALA (C18:3) was the most abundant, followed by oleic (C18:1) and linoleic (C18:2) acids. Additionally, quantitative real-time RT-PCR analyses of 10 key seed oil synthesis genes in the three tree peony species revealed that FAD3, FAD2, β-PDHC, LPAAT, and Oleosin gene expression levels positively correlate with total FA content and rate of accumulation. Specifically, the abundance of FAD3 transcripts in P. rockii compared with P. potaninii, and P. lutea suggests that FAD3 might play an important role in synthesis of ALA via phosphatidylcholine-derived pathway. Overall, comparative analyses of FA content and composition in three different peony species revealed a correlation between efficient lipid accumulation and lipid gene expression during seed development. Further characterization and metabolic engineering of these key genes from peonies will allow for subsequent improvement of tree peony oil quality and production.

Highlights

Tree peony is a perennial deciduous shrub, belongs to section Moutan of the genus Paeonia in the family Paeoniaceae (Picerno et al, 2011; Li et al, 2012)
To identify distinct biochemical and molecular differences that contribute to diverse levels of oil accumulation among closely related wild tree peony species, P. rockii, P. potaninii, and P. lutea, each representing a cluster with varying levels of fatty acid (FA) content in mature seeds (Figure 1) were selected for further study
Alpha-linolenic acid cannot be synthesized by the human body (Sinclair et al, 2002; Liu et al, 2012), and yet is an essential precursor for the synthesis of eicosapentaenoic acid and docosahexaenoic acid, which exert a wide range of biological activities and prophylactic effects (Shahidi and Miraliakbari, 2004; Shahidi and Miraliakbari, 2005)

Summary

Introduction

Tree peony is a perennial deciduous shrub, belongs to section Moutan of the genus Paeonia in the family Paeoniaceae (Picerno et al, 2011; Li et al, 2012). Peony seeds are a good source of edible oil with higher percentage of unsaturated FA (92%). Α-linolenic acid (ALA/18:3), an ω-3 PUFA is the most predominant (∼45% of the total FA content) FA in peony seed, 18:3 (Li et al, 2015a,b). Linoleic acid (18:2), an ω-6 FA and ALA are essential for humans as they cannot synthesize these two FAs and must be obtained from diet (Zhou et al, 2014). In tree peony seed oil while 18:3 accounts for ∼45% of the total FA content, 18:2 is less than 25% (Li et al, 2015a,b). Especially being a woody oil crop is an attractive model for dissecting PUFA metabolic pathways and develop an alternative source of healthy edible oil

Methods

Results

Conclusion