Metabolic control analysis is helpful for informed genetic manipulation of oilseed rape (Brassica napus) to increase seed oil content

Abstract

Top–down control analysis (TDCA) is a useful tool for quantifying constraints on metabolic pathways that might be overcome by biotechnological approaches. Previous studies on lipid accumulation in oilseed rape have suggested that diacylglycerol acyltransferase (DGAT), which catalyses the final step in seed oil biosynthesis, might be an effective target for enhancing seed oil content. Here, increased seed oil content, increased DGAT activity, and reduced substrate:product ratio are demonstrated, as well as reduced flux control by complex lipid assembly, as determined by TDCA in Brassica napus (canola) lines which overexpress the gene encoding type-1 DGAT. Lines overexpressing DGAT1 also exhibited considerably enhanced seed oil content under drought conditions. These results support the use of TDCA in guiding the rational selection of molecular targets for oilseed modification. The most effective lines had a seed oil increase of 14%. Moreover, overexpression of DGAT1 under drought conditions reduced this environmental penalty on seed oil content.

Multigene Engineering of Triacylglycerol Metabolism Boosts Seed Oil Content in Arabidopsis

“…However, WRI1 predominantly targets the expression of genes associated with glycolysis and fatty acid synthesis (Baud et al, 2007;To et al, 2012), while DGAT1 catalyzes the final step in the assembly of TAG from DAG and acyl-CoA (Katavic et al, 1995). Top-down metabolic control analysis studies suggest that a significant proportion of control over TAG synthesis lies within both portions of the metabolic pathway (Weselake et al, 2008;Tang et al, 2012). The additive effect of overexpression of these two genes supports this conclusion.…”

“…Metabolic control over oil production in developing seeds resides in both the production of fatty acids and their utilization for TAG assembly (Weselake et al, 2008;Tang et al, 2012). Previous studies have shown that overexpression of the WRI1 transcription factor activates the expression of multiple genes associated with lower glycolysis and fatty acid synthesis (Baud et al, 2007;To et al, 2012) and can enhance oil content in seeds of Arabidopsis (Cernac and Benning, 2004).…”

“…The majority of control that is exerted over the rate of carbon flux through a metabolic pathway rarely lies predominantly with one step and is usually distributed between many (Fell, 1997). Top-down metabolic control analysis, performed on developing seeds, suggests that this is the case for oil synthesis (Weselake et al, 2008;Tang et al, 2012). Constraint-based metabolic modeling also predicts that seed oil content is sensitive to multiple reactions (Schwender and Hay, 2012).…”

Predictive Modeling of Biomass Component Tradeoffs in Brassica napus Developing Oilseeds Based on in Silico Manipulation of Storage Metabolism

“…The same kind of comparison can be applied to a case where TAG assembly was manipulated. Weselake et al (2008) found a 4-fold increase in diacylglycerol acyltransferase activity, corresponding to an approximately 5% increase in oil content (Table VI). The diacylglycerol acyltransferase synthesis is associated with the TAG synthesis reaction (511), and here the tradeoff model predicts a 1.13-fold increase in reaction 511.…”

“…The literature often considers the control over oil accumulation to be shared mostly between reactions of fatty acid synthesis and TAG assembly (Ramli et al, 2002;Thelen and Ohlrogge, 2002;Weselake et al, 2008). Relevant reactions in bna572 are TAG responsive, but according to Table IV, those reactions are not among those with highest responsiveness.…”