Ectopic expression of WRI1 affects fatty acid homeostasis in Brachypodium distachyon vegetative tissues

Abstract

Triacylglycerol (TAG) is a storage lipid used for food purposes and as renewable feedstock for biodiesel production. WRINKLED1 (WRI1) is a transcription factor, which governs fatty acid (FA) synthesis and indirectly TAG accumulation in oil storing plant tissues and its ectopic expression has led to TAG accumulation in vegetative tissues of different dicotyledonous plants. The ectopic expression of BdWRI1 in the grass Brachypodium (Brachypodium distachyon) induced the transcription of predicted genes involved in glycolysis and FA biosynthesis, and TAG content was increased up to 32.5-fold in 8-week-old leaf blades. However, the ectopic expression of BdWRI1 also caused cell death in leaves, which has not been previously observed in dicotyledonous plants such as Arabidopsis (Arabidopsis thaliana). Lipid analysis indicated that the free FA content was 2.0-fold elevated in BdWRI1-expressing leaf blades of Brachypodium. The transcription of predicted genes involved in β-oxidation was induced. In addition, linoleic fatty acid treatment caused cell death in Brachypodium leaf blades, an effect that was reversed by addition of the FA biosynthesis inhibitor cerulenin. Taken together, ectopic expression of BdWRI1 in Brachypodium enhances FA biosynthesis and TAG accumulation in leaves as expected but also leads to increased free FA content, which has cytotoxic effects leading to cell death. Thus, while WRI appears to ubiquitously affect FA biosynthesis and TAG accumulation in diverse plants, its ectopic expression can lead to undesired side effects depending on the context of the specific lipid metabolism of the respective plant species.