The Family of Peanut Fatty Acid Desaturase Genes and a Functional Analysis of Four \u03c9-3 AhFAD3 Members

Zhenying Peng,Jingjing Meng,Jian Ruan,Zhimeng Zhang,Feng Guo,Hong Ding,Shubo Wan,Lei Shan,Xinguo Li,Haiying Tian

doi:10.1007/s11105-019-01191-0

Abstract

The synthesis of α-linolenic acid (ALA) requires the activity of ω-3 fatty acid desaturases (ω-3 FADs). The quality of peanut oil would be much improved if the content of ALA could be increased. A scan of the peanut genome revealed that it harbored 36 FAD genes, mapping to 16 of the species’ 20 chromosomes. A phylogenetic analysis concluded that these genes belonged to six sub-families, namely stearoyl-acyl-acyl carrier protein desaturases (SAD), FAD2, FAD3, FAD4/5, FAD6 and FAD7/8. Of these, FAD3 and FAD7/8 encoded ω-3 FADs, while genes belonging to the other four sub-families encoded ω-6 FADs. Based on RNA-Seq data, each of the 36 FAD genes was shown to be transcribed in non-stressed plants, but there was variation between them with respect to which organs they were transcribed in. Four ω-3 AhFAD3 genes were functionally characterized; when expressed in Arabidopsis thaliana protoplasts, each was localized mainly in the endoplasmic reticulum, while within peanut, the genes were more strongly transcribed in the developing seed than in either the root or the leaf. When constitutively expressed in Arabidopsis thaliana, both the total fatty acid content of the seed and the relative contribution of ALA were increased. The transgenic seedlings also exhibited an improved level of survival when challenged by salinity stress.

Highlights

Sequence Analysis of FADsThe seeds of peanut (Arachis hypogaea L.) represent an important source of culinary oil, the fatty acid content of which is dominated by oleic acid (C18:1, about 50% of the total oil content) and linoleic acid (C18:2, about 30% of the total oil content); its content of linolenic acid (C18:3) is very low (Li et al 2012). α-linolenic acid (ALA) is an essential fatty acid in the human diet as it cannot be synthesized in the body, since humans lack any ω-3 fatty acid desaturases (ω-3 FADs) (Baker et al 2016)
Cultivated peanut is an allotetraploid formed following a natural hybridization between the two diploid species Ar. duranensis and Ar. ipaensis (Bertioli et al 2016)
A previous report has documented that A. duranensis harbors FAD genes, while A. ipaensis harbors (Ruan et al 2018)

Summary

Introduction

Sequence Analysis of FADsThe seeds of peanut (Arachis hypogaea L.) represent an important source of culinary oil, the fatty acid content of which is dominated by oleic acid (C18:1, about 50% of the total oil content) and linoleic acid (C18:2, about 30% of the total oil content); its content of linolenic acid (C18:3) is very low (about 0.1%) (Li et al 2012). α-linolenic acid (ALA) is an essential fatty acid in the human diet as it cannot be synthesized in the body, since humans lack any ω-3 fatty acid desaturases (ω-3 FADs) (Baker et al 2016). A number of examples have been presented which confirm that the activity of ω-3 FADs affects the plant stress response: these include the up-regulation by low temperature of a FAD gene in Arabidopsis thaliana plants (Chen et al 2018; Gibson et al 1994) and a demonstration that the over-expression of an ω-3 FAD improves chilling tolerance in tomato (Yu et al 2009). Many FAD genes are known to experience alternative splicing (AS), a post-transcriptional phenomenon which is important for plant growth, development, signal transduction, flowering and the response to various environmental cues (Blencowe 2006; Reddy et al 2013; Remy et al 2014; Stamm et al 2005; Tang et al 2016; Yang et al 2014; Zhang et al 2016). In soybean, the abundance of specific splicing variants of both GmFAD3A and GmFAD7 respond to low temperature stress (Román et al 2012)

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Conclusion