Abstract
Arabidopsis thaliana seed maturation is accompanied by the deposition of storage oil, rich in the essential ω-3 polyunsaturated fatty acid α-linolenic acid (ALA). The synthesis of ALA is highly responsive to the level of fatty acid desaturase3 (FAD3) expression, which is strongly upregulated during embryogenesis. By screening mutants in leafy cotyledon1 (LEC1)-inducible transcription factors using fatty acid profiling, we identified two mutants (lec1-like and bzip67) with a seed lipid phenotype. Both mutants share a substantial reduction in seed ALA content. Using a combination of in vivo and in vitro assays, we show that bZIP67 binds G-boxes in the FAD3 promoter and enhances FAD3 expression but that activation is conditional on bZIP67 association with LEC1-like (L1L) and nuclear factor-YC2 (NF-YC2). Although FUSCA3 and abscisic acid insensitive3 are required for L1L and bZIP67 expression, neither protein is necessary for [bZIP67:L1L:NF-YC2] to activate FAD3. We conclude that a transcriptional complex containing L1L, NF-YC2, and bZIP67 is induced by LEC1 during embryogenesis and specifies high levels of ALA production for storage oil by activating FAD3 expression.
Highlights
Seed maturation in higher plants is associated with the deposition of storage reserves, such as oil, carbohydrates, and proteins (Baud and Lepiniec, 2010)
Several studies have established that ectopic expression of LEAFY COTYLEDON1 (LEC1) leads to the induction of genes associated with the embryo maturation program, and results in accumulation of storage oil (Lotan et al, 1998; Mu et al, 2008)
To identify transcription factors (TFs) that might lie downstream of LEC1 in the regulatory network that controls seed oil content and composition, published Affymetrix Ath1 chip microarray data were used to select those genes listed on the Arabidopsis Transcription Factor Database that are more than fourfold upregulated in both LEC1-overexpressing seedlings (Mu et al, 2008) and wild-type developing seeds
Summary
Seed maturation in higher plants is associated with the deposition of storage reserves, such as oil (triacylglycerol), carbohydrates, and proteins (Baud and Lepiniec, 2010). Seed storage reserves provide a major source of nutrition for humans and livestock, and serve as feedstock for a broad variety of industrial applications (Lu et al, 2011). Genetic studies have revealed that a complex network of transcriptional master regulators orchestrates the seed maturation program, of which storage reserve deposition is an integral part (Vicente-Carbajosa and Carbonero, 2005; Santos-Mendoza et al, 2008). LEC2, FUS3, and ABI3 encode plantspecific transcription factors (TFs) that are closely related and contain a conserved B3 DNA binding domain (Giraudat et al, 1992; Luerssen et al, 1998; Stone et al, 2001)
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