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.

BackgroundDuckweeds, i.e., members of the Lemnoideae family, are amongst the smallest aquatic flowering plants. Their high growth rate, aquatic habit and suitability for bio-remediation make them strong candidates for biomass production. Duckweeds have been studied for their potential as feedstocks for bioethanol production; however, less is known about their ability to accumulate reduced carbon as fatty acids (FA) and oil.ResultsTotal FA profiles of thirty duckweed species were analysed to assess the natural diversity within the Lemnoideae. Total FA content varied between 4.6% and 14.2% of dry weight whereas triacylglycerol (TAG) levels varied between 0.02% and 0.15% of dry weight. Three FA, 16:0 (palmitic), 18:2Δ9,12 (Linoleic acid, or LN) and 18:3Δ9,12,15 (α-linolenic acid, or ALA) comprise more than 80% of total duckweed FA. Seven Lemna and two Wolffiela species also accumulate polyunsaturated FA containing Δ6-double bonds, i.e., GLA and SDA. Relative to total FA, TAG is enriched in saturated FA and deficient in polyunsaturated FA, and only five Lemna species accumulate Δ6-FA in their TAG. A putative Δ6-desaturase designated LgDes, with homology to a family of front-end Δ6-FA and Δ8-spingolipid desaturases, was identified in the assembled DNA sequence of Lemna gibba. Expression of a synthetic LgDes gene in Nicotiana benthamiana resulted in the accumulation of GLA and SDA, confirming it specifies a Δ6-desaturase.ConclusionsTotal accumulation of FA varies three-fold across the 30 species of Lemnoideae surveyed. Nine species contain GLA and SDA which are synthesized by a Δ6 front-end desaturase, but FA composition is otherwise similar. TAG accumulates up to 0.15% of total dry weight, comparable to levels found in the leaves of terrestrial plants. Polyunsaturated FA is underrepresented in TAG, and the Δ6-FA GLA and SDA are found in the TAG of only five of the nine Lemna species that produce them. When present, GLA is enriched and SDA diminished relative to their abundance in the total FA pool.

Self-assembly of amyloid polypeptides (1) imparts biological effects depending on the size in over 20 amyloid diseases and (2) produces useful yet relatively untapped biomaterials. Unfortunately, our understanding of amyloid polypeptides, as related to biomedical implications and biomaterial applications, is limited by their self-assembling nature. In this study, we report the creation of a dual peptide system, where a pair of β-amyloid (Aβ) variants are not self-assembled but hetero-assembled in the presence of their assembly partners. We provide evidence that the resulting hetero-assemblies share molecular, structural and morphological similarities with typical amyloid self-assemblies formed by a single polypeptide (e.g., Aβ). We anticipate that our dual peptide system may readily be adapted for precise control of amyloid assembly, for the study of size-dependent neurotoxicity and precise fabrication of amyloid biomaterials.