Studies on transcription factors involved in seed oil biosynthesis
Canola (Brassica napus) oil has immense economic value due to its use as food. The production of biodiesel has led to the recent increase in the demand for canola oil, and further reinforced the need to improve the oil content and composition of canola seeds. The content and quality of canola oil is dependent on the process of fatty acid biosynthesis and accumulation of triacylglycerols (TAGs) during seed development. The biochemical pathways leading to the synthesis of fatty acids and TAGs are thoroughly understood, and many of the genes encoding the metabolic enzymes involved in this pathway have been isolated and functionally characterized. Despite comprehensive understanding of fatty acid and TAG biosynthesis, alternate factors and genes involved in the modification of seed oil content and composition are being investigated. This has initiated a new sector of research focusing on a series of transcription factors: LEAFY COTYLEDON1 (LEC1), LEAFY COTYLEDON2 (LEC2), FUSCA3 (FUS3) and WRINKLED1 (WRI1), which play a key role during embryo and seed development. Previous studies in Arabidopsis have demonstrated that the noted transcription factors influence the synthesis and accumulation of oil during seed development. These findings have prompted the design of two studies with the objective of further characterizing the role of these genes. In the first study, a homolog of Arabidopsis LEC1 was isolated from Brassica napus (Bn) microspore derived embryos. BnLEC1 contained the same distinct features identified in LEC1 genes from other plant species. BnLEC1 was inserted into an expression vector, which was subsequently used to transform Arabidopsis plants. The transgenic lines were characterized by differences in seed oil composition, and one line showed a reduction in the number of seeds counted per silique. Expression analysis revealed that the transgene was not expressed in the transgenic lines. To account for the discrepant findings, the possibility of endogenous gene silencing mechanisms suppressing transgene expression has been discussed. As an extension of this research, a second study assessed the differential expression of LEC1, LEC2, FUS3 and WRI1 in double haploid Brassica napus lines characterized by different levels of seed oil content. The expression level of the noted genes was determined at 7, 14, 21 and 28 days after pollination. Numerous changes in the transcript level were observed, but the trends were not consistent among high and low oil content lines.
LEAFY COTYLEDON1, Brassica napus