Abstract
Triacylglycerol (TAG) is an energy-rich reserve in plant seeds that is composed of glycerol esters with three fatty acids. Since TAG can be used as a feedstock for the production of biofuels and bio-chemicals, producing TAGs in vegetative tissue is an alternative way of meeting the increasing demand for its usage. The WRINKLED1 (WRI1) gene is a well-established key transcriptional regulator involved in the upregulation of fatty acid biosynthesis in developing seeds. WRI1s from Arabidopsis and several other crops have been previously employed for increasing TAGs in seed and vegetative tissues. In the present study, we first identified three functional CsWRI1 genes (CsWRI1A. B, and C) from the Camelina oil crop and tested their ability to induce TAG synthesis in leaves. The amino acid sequences of CsWRI1s exhibited more than 90% identity with those of Arabidopsis WRI1. The transcript levels of the three CsWRI1 genes showed higher expression levels in developing seeds than in vegetative and floral tissues. When the CsWRI1A. B, or C was introduced into Arabidopsis wri1-3 loss-of-function mutant, the fatty acid content was restored to near wild-type levels and percentages of the wrinkled seeds were remarkably reduced in the transgenic lines relative to wri1-3 mutant line. In addition, the fluorescent signals of the enhanced yellow fluorescent protein (eYFP) fused to the CsWRI1 genes were observed in the nuclei of Nicotiana benthamiana leaf epidermal cells. Nile red staining indicated that the transient expression of CsWRI1A. B, or C caused an enhanced accumulation of oil bodies in N. benthamiana leaves. The levels of TAGs was higher by approximately 2.5- to 4.0-fold in N. benthamiana fresh leaves expressing CsWRI1 genes than in the control leaves. These results suggest that the three Camelina WRI1s can be used as key transcriptional regulators to increase fatty acids in biomass.
Highlights
Camelina sativa L. is an underdeveloped oil crop in the family Brassicaceae, which has several advantages in the agronomic and environmental context over the current developed oil crops
In order to identify the factors involved in the accumulation of higher oil content in Camelina, we first focused on identifying the homologous genes of Arabidopsis WRINKLED1 (AtWRI1) in two different Camelina genome databases2,3
All three CsWRI1 cDNAs were able to partially complement the wri1-3 phenotype, as evidenced by a greater seed fatty acid content compared to the mutant and the vectoronly transformant control irrespective of expression on the basis of seed weight or seed number (Figures 6A–C, Supplementary Table 5). These results suggest that CsWRI1A, B, and C variants are each potentially involved in regulating the level of fatty acid biosynthesis in developing seeds
Summary
Camelina sativa L. is an underdeveloped oil crop in the family Brassicaceae, which has several advantages in the agronomic and environmental context over the current developed oil crops. Camelina seed oil is composed of 35–45% triacylglycerol (TAG), which has a high proportion of polyunsaturated fatty acids (PUFAs) (Lu and Kang, 2008; Bansal and Durrett, 2016). Breeding and genetic engineering programs can generate new varieties of Camelina with a lower PUFA content for stable oxidation (Kang et al, 2011; Nguyen et al, 2013). Camelina can be transformed using the Agrobacterium-mediated flower-dip method, which is a relatively simple and rapid route to generating transgenic plants with superior agronomic traits (Lu and Kang, 2008; Liu et al, 2012). The whole genome sequence and seed transcriptome data present valuable resources for the understanding of the function of genes involved in oil biosynthesis in Camelina seeds (Hutcheon et al, 2010; Nguyen et al, 2013; Kagale et al, 2014)
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