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 a renewable feedstock for biodiesel production. WRINKLED1 (WRI1) is a transcription factor that 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 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 observed previously in dicotyledonous plants such as Arabidopsis (Arabidopsis thaliana). Lipid analysis indicated that the free FA content was 2-fold elevated in BdWRI1-expressing leaf blades of B. distachyon. The transcription of predicted genes involved in b-oxidation was induced. In addition, linoleic FA treatment caused cell death in B. distachyon leaf blades, an effect that was reversed by the addition of the FA biosynthesis inhibitor cerulenin. Taken together, ectopic expression of BdWRI1 in B. distachyon 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.

Expression of Camelina WRINKLED1 Isoforms Rescue the Seed Phenotype of the Arabidopsis wri1 Mutant and Increase the Triacylglycerol Content in Tobacco Leaves

“…A limited number of WRI1 genes identified from model plants, such as Arabidopsis for dicots (Cernac and Benning, 2004), B. distachyon for temperate grasses (Yang et al, 2015), and B. napus (Liu et al, 2010) and maize (Shen et al, 2010) for crops, have been tested for their ability to enhance the oil content in developing seeds and vegetative tissues (Grimberg et al, 2015). We tested the potential of each Camelina WRI1 isoform to enhance the vegetable oil biosynthesis in N. benthamiana leaves.…”

“…Since WRI1 is a regulator for lipid accumulation even in non-seed tissues (Kilaru et al, 2015), WRI1 paralogs distinct from seed-specific WRI1 were observed in the tallow layer, the non-seed tissue, in Chinese tallow ( Triadica sebifera ), which is a valuable oilseed-producing tree (Divi et al, 2016). In yet another study, the ectopic expression of B. distachyon WRI1 isolated from the vegetative tissues induced an increase in TAG content and simultaneously resulted in cell death in the leaf blades (Yang et al, 2015). Ectopic expression of WRI1 s from diverse species and tissues in leaves of N. benthamiana has been shown to result in the production of TAG content ranging from 0.05 to 2.2%.…”

“…In addition to seeds, WRI1 homologs have been identified in non-seed tissues containing oil, such as the stem of poplar ( Populus trichocarpa L.), tuber parenchyma of nutsedge ( Cyperus esculentus L.), and leaf blades of Brachypodium distachyon L. Beauv. (Grimberg et al, 2015; Yang et al, 2015). Overexpression of the WRI1 genes contributed to increased TAG levels in the seeds and vegetative tissues.…”

Transport and transcriptional regulation of oil production in plants

“…[66] In maize and Arabidopsis, WRI1 regulates the genes involved in FA biosynthesis, such as ACCase subunits, ACP1, and KAS1, through direct binding to AW box in their promoter regions. [66,79,80] Arabidopsis PII plays a role in the fine tuning of fatty acid biosynthesis and is directly controlled by WRI1. An increase in FA production was accompanied by a maximal content of PII Arabidopsis.…”

Potato tuber expression of Arabidopsis WRINKLED1 increase triacylglycerol and membrane lipids while affecting central carbohydrate metabolism

“…It belongs to the AP2/EREB domain family and triggers the expression of genes involved in glycolysis and fatty acid synthesis (Cernac and Benning, 2004;Focks and Benning, 1998). Expression of maize homologs complementing the WRINKLED1 mutation in Arabidopsis and heterologous expression in leaf tissue of Arabidopsis have shown WRINKLED1 to have the capacity for complementation of deficiencies across species as well as to ectopically induce oil accumulation and heterologously enhance oil content in seeds (An and Suh, 2015;Pouvreau et al, 2011;Sanjaya et al, 2011;Yang et al, 2015). Recently, also protein structural properties have been investigated to elucidate and enhance the function of the WRINKLED1 transcription factor .…”