Born of frustration: the emergence of Camelina sativa as a platform for lipid biotechnology

Abstract

The emerging crop Camelina sativa (L.) Crantz (camelina) is a Brassicaceae oilseed with a rapidly growing reputation for the deployment of advanced lipid biotechnology and metabolic engineering. Camelina is recognized by agronomists for its traits, including yield, oil/protein content, drought tolerance, limited input requirements, plasticity, and resilience. Its utility as a platform for metabolic engineering was then quickly recognized, and biotechnologists have benefited from its short life cycle and facile genetic transformation, producing numerous transgenic interventions to modify seed lipid content and generate novel products. The desire to work with a plant that is both a model and crop has driven the expansion of research resources for camelina, including increased availability of genome and other -omics data sets. Collectively, the expansion of these resources has established camelina as an ideal plant to study the regulation of lipid metabolism and genetic improvement. Furthermore, the unique characteristics of camelina enables the design-build-test-learn cycle to be transitioned from the controlled environment to the field. Complex metabolic engineering to synthesize and accumulate high levels of novel fatty acids and modified oils in seeds can be deployed, tested, and undergo rounds of iteration in agronomically relevant environments. Engineered camelina oils are now increasingly being developed and used to sustainably supply improved nutrition, feed, biofuels, and fossil fuel replacements for high-value chemical products. In this review, we provide a summary of seed fatty acid synthesis and oil assembly in camelina, highlighting how discovery research in camelina supports the advance of metabolic engineering toward the predictive manipulation of metabolism to produce desirable bio-based products. Further examples of innovation in camelina seed lipid engineering and crop improvement are then provided, describing how technologies (e.g. genetic modification [GM], gene editing [GE], RNAi, alongside GM and GE stacking) can be applied to produce new products and denude undesirable traits. Focusing on the production of long chain polyunsaturated omega-3 fatty acids in camelina, we describe how lipid biotechnology can transition from discovery to a commercial prototype. The prospects to produce structured triacylglycerol with fatty acids in specified stereospecific positions are also discussed, alongside the future outlook for the agronomic uptake of camelina lipid biotechnology.

Figure 1.

Camelina seed lipid biosynthesis. A) An illustration of endogenous cellular lipid synthesis and assembly pathways, including the following selected genes: FAS, fatty acid synthase; KASII, beta ketoacyl acyl carrier protein synthase II; SAD, stearoyl-acyl carrier protein desaturase; FAD, fatty acid desaturase; FAX1, fatty acid export 1; LACS9, long chain acyl—CoA synthetase 9; FAE1, fatty acid elongation 1; LPCAT, lysophosphatidylcholine acyltransferase; DGAT, diacylglycerol acyltransferase; PDAT, phospholipid:diacylglycerol acyltransferase; PLC, phospholipase C; PLD, phospholipase D; CPT, diacylglycerol cholinephosphotransferase; PDCT, phosphatidylcholine diacylglycerol cholinephosphotransferase; GPAT, Glycerol-3-phosphate acyltransferase; LPAAT, lysophosphatidyl acyltransferase; PAP, phosphatidate phosphatase. B) Heatmap showing the expression of selected C. sativa genes during seed development generated using https://github.com/richysix/bioinf-gen/blob/master/docs/gene_expr_heatmap/gene_expr_heatmap.md (B). The color scale represents normalized counts calculated by DESeq2. RNA sequencing reads generated by Kagale et al. (2016) (accessions SRX472942, SRX472943, SRX472945, and SRX472946) were aligned to the C. sativa reference genome (Kagale et al. 2014) (accession JFZQ00000000) using TopHat and quantified at the gene level with HTSeq. Key to seed stages: Early seed development (ESD), Early mid seed development (EMSD), Late mid seed development (LMSD), and Late seed development (LSD).

Figure 2.

Camelina as a platform of metabolic engineering. A) Field-grown camelina seed engineered with a range of traits including omega-3 and ketocarotenoids (seeds from modified camelina are shown clockwise) 1. Wildtype; 2. RUBY (betaline); 3. Astaxanthin; and 4. tt2 mutant (MYB); B) Representative MSI study (camelina seed section; coloring indicates abundance—red high and green low) highlighting the asymmetric accumulation (in the embryonic axis tip) of a selected PC molecular species containing novel fatty acids (C22:6/C22:6; see Usher et al. 2017); C) Field testing (Rothamsted Research, UK) of Camelina sativa engineered for the production of omega-3 long chain polyunsaturated fatty acids (EPA and DHA).