Metabolic engineering of sugarcane to accumulate energy‐dense triacylglycerols in vegetative biomass

Abstract

SummaryElevating the lipid content in vegetative tissues has emerged as a new strategy for increasing energy density and biofuel yield of crops. Storage lipids in contrast to structural and signaling lipids are mainly composed of glycerol esters of fatty acids, also known as triacylglycerol (TAG). TAGs are one of the most energy-rich and abundant forms of reduced carbon available in nature. Therefore, altering the carbon-partitioning balance in favour of TAG in vegetative tissues of sugarcane, one of the highest yielding biomass crops, is expected to drastically increase energy yields. Here we report metabolic engineering to elevate TAG accumulation in vegetative tissues of sugarcane. Constitutive co-expression of WRINKLED1 (WRI1), diacylglycerol acyltransferase1-2 (DGAT1-2) and oleosin1 (OLE1) and simultaneous cosuppression of ADP-glucose pyrophosphorylase (AGPase) and a subunit of the peroxisomal ABC transporter1 (PXA1) in transgenic sugarcane elevated TAG accumulation in leaves or stems by 95-or 43-fold to 1.9% or 0.9% of dry weight (DW), respectively, while expression or suppression of one to three of the target genes increased TAG levels by 1.5-to 9.5-fold. Accumulation of TAG in vegetative progeny plants was consistent with the results from primary transgenics and contributed to a total fatty acid content of up to 4.7% or 1.7% of DW in mature leaves or stems, respectively. Lipid droplets were visible within mesophyll cells of transgenic leaves by confocal fluorescence microscopy. These results provide the basis for optimizations of TAG accumulation in sugarcane and other high yielding biomass grasses and will open new prospects for biofuel applications.

Lipid Droplet-Associated Proteins (LDAPs) Are Required for the Dynamic Regulation of Neutral Lipid Compartmentation in Plant Cells

“…bioenergy) content of vegetative biomass. Recent studies by multiple groups, including our own, suggest that plants are remarkably amenable to an accumulation of elevated amounts of LDs and TAG in leaves (James et al, 2010;Fan et al, 2014;Vanhercke et al, 2014;Cai et al, 2015;Zale et al, 2016), thus providing a potential means for producing significantly higher amounts of biofuels in nonfood crop plants. Given the increasing evidence that LDs are likely to be important for the plant stress response, it will be important to determine how the directed proliferation of LDs will impact the adaptation of plants to environmental stress.…”

Sugar Potentiation of Fatty Acid and Triacylglycerol Accumulation

“…In the storage tissues of some varieties of sugarcane, sugar levels can approach 650 mM (Welbaum and Meinzer, 1990) without stimulating TAG accumulation in stems (Zale et al, 2016). One possible explanation is that the majority of Suc is compartmentalized in vacuoles, resulting in relatively low levels of Suc in the cytoplasm that are available as carbon skeletons for FA synthesis.…”

Transport and transcriptional regulation of oil production in plants

“…[97] Overexpression of WRI1, DGAT1, oleosin 1 (OLE1) and suppression of PXA1 and ADP-glucose pyrophosphorylase enhanced TAG production in transgenic sugarcane leaves and stems by 95 and 43 fold, respectively, compared to wild type. [98] Disruption of PDAT1 and SDP1 TAG lipase also increases TAG accumulation in Arabidopsis. [99] Although a-linolenic acid (ALA; C18:3 cisD9, 12, 15) is desirable for human health, its chemical instability is one major reason for creation of side products trans-fats during food processing.…”