Abstract
The peanut (Arachis hypogaea L.) is an important oilseed crop worldwide. Compared to other common edible vegetable oils, peanut oil contains a higher content of saturated fatty acids (SFAs), approximately 20–40% of which are very long chain fatty acids (VLCFAs). To understand the basis for this oil profile, we interrogated genes for peanut β-ketoacyl-CoA synthase (KCS), which is known to be a key enzyme in VLCFA biosynthesis. A total of 30 AhKCS genes were identified in the assembled genome of the peanut. Based on transcriptome data, nine AhKCS genes with high expression levels in developing seeds were cloned and expressed in yeast. All these AhKCSs could produce VLCFAs but result in different profiles, indicating that the AhKCSs catalyzed fatty acid elongation with different substrate specificities. Expression level analysis of these nine AhKCS genes was performed in developing seeds from six peanut germplasm lines with different VLCFA contents. Among these genes, the expression levels of AhKCS1 or AhKCS28 were, 4–10-fold higher than that of any other AhKCS. However, only the expression levels of AhKCS1 and AhKCS28 were significantly and positively correlated with the VLCFA content, suggesting that AhKCS1 and AhKCS28 were involved in the regulation of VLCFA content in the peanut seed. Further subcellular localization analysis indicated that AhKCS1 and AhKCS28 were located at the endoplasmic reticulum (ER). Overexpression of AhKCS1 or AhKCS28 in Arabidopsis increased the contents of VLCFAs in the seed, especially for very long chain saturated fatty acids (VLCSFAs). Taken together, this study suggests that AhKCS1 and AhKCS28 could be key genes in regulating VLCFA biosynthesis in the seed, which could be applied to improve the health-promoting and nutritional qualities of the peanut.
Highlights
The peanut (Arachis hypogaea L.) is a widely cultivated oilseed crop in tropical and subtropical regions, which provides a significant source of protein, folate, tocopherol, phytosterols, polyphenolics such as resveratrol, fiber, and edible oil (Bertioli et al, 2015; Han, 2016; Bertioli et al, 2019)
The alternatively spliced transcripts were identified in AhKCS14 and AhKCS22 genes (Table 1), implying that different isoforms may play different roles in the development of the peanut
There were four peaks for C20:0, C22:0, C22:1, and C26:0 identified in yeast cells with AhKCS4 and AhKCS17 (Table 2). These results suggested that the substrate specificities of AhKCSs differed: AhKCS13 and AhKCS29 tended to accumulate C20:0; AhKCS4 and AhKCS17 preferentially stored C26 fatty acids; AhKCS1, AhKCS10, AhKCS23, AhKCS25, and AhKCS28 actively produced a variety of very long chain fatty acids (VLCFAs)
Summary
The peanut (Arachis hypogaea L.) is a widely cultivated oilseed crop in tropical and subtropical regions, which provides a significant source of protein, folate, tocopherol, phytosterols, polyphenolics such as resveratrol, fiber, and edible oil (Bertioli et al, 2015; Han, 2016; Bertioli et al, 2019). Fatty acid composition is the main factor in determining the nutritional value and application purpose of vegetable oil (Napier and Graham, 2010; Napier et al, 2014). Peanut oil contains ∼20% saturated fatty acids (SFAs), which is higher than that in many commercial vegetable oils (Wang et al, 2013; Giakoumis, 2018). SFAs are enriched in VLCSFAs, including arachidic acid (C20:0), behenic acid (C22:0), and lignoceric acid (C24:0) (Wang et al, 2013; Giakoumis, 2018). Reducing VLCFA content in the peanut is a prime target to improve the nutritional value of peanuts and peanut oil
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