Metabolic engineering for enhanced oil in biomass

Authors: VANHERCKE, THOMAS - COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH ORGANISATION (CSIRO); Dyer, John; MULLEN, ROBERT - UNIVERSITY OF GUELPH; KILARU, ARUNA - EAST TENNESSEE STATE UNIVERSITY; RAHMAN, MAHBUBUR - EAST TENNESSEE STATE UNIVERSITY; PETRIE, JAMES - COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH ORGANISATION (CSIRO); GREEN, ALLAN - COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH ORGANISATION (CSIRO); YURCHENKO, OLGA - FORMER ARS EMPLOYEE; SINGH, SURINDER - COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH ORGANISATION (CSIRO)

Submitted to: Progress in Lipid Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2019
Publication Date: 2/26/2019
Citation: Vanhercke, T., Dyer, J.M., Mullen, R.T., Kilaru, A., Rahman, M.M., Petrie, J.R., Green, A.G., Yurchenko, O., Singh, S.P. 2019. Metabolic engineering for enhanced oil in biomass. Progress in Lipid Research. 74:103-129. https://doi.org/10.1016/j.plipres.2019.02.002.
DOI: https://doi.org/10.1016/j.plipres.2019.02.002

Interpretive Summary: Plant oils are energy-dense feedstocks used for a variety of purposes including foods, feeds, biofuels, and industrial chemicals. Finite mineral oil reserves, growing world population and increasing environmental awareness are all likely to add considerable pressure on the future supply of this highly valuable commodity. Traditionally, plant oils are sourced either from oilseeds or tissues surrounding the seed (the mesocarp). Most vegetative tissues, which constitute the majority of the plant biomass, however, accumulate relatively low levels of oil. Over the past 10 years, scientists have made significant advancements in understanding the molecular mechanisms of oil production in vegetative biomass, resulting in novel approaches to dramatically increase the oil content in plant leaves and stems. This manuscript provides a comprehensive overview of this work, identifies new and emerging areas of research, and outlines challenges that lie ahead in developing and utilizing high biomass-high oil crops for sustainable bioenergy production.

Technical Abstract: The world is hungry for energy. Plant oils in the form of triacylglycerol (TAG) are one of the most reduced storage forms of carbon found in nature and hence represent an excellent source of energy. The myriad of applications for plant oils range across foods, feeds, biofuels, and chemical feedstocks as a unique substitute for petroleum derivatives. Finite mineral oil reserves, growing world population and increasing environmental awareness are all likely to add considerable pressure on the future supply of this highly valuable commodity. Traditionally, plant oils are sourced either from oilseeds or tissues surrounding the seed (mesocarp). Most vegetative tissues, which constitute the majority of the plant biomass, however, accumulate relatively low levels of TAG. This is particularly the case for photosynthetic organs where carbon is shunted into transitory starch as the major storage form. Metabolic engineering of vegetative tissues to improve the low-intrinsic TAG-biosynthetic capacity has recently attracted significant attention as a novel, sustainable and potentially high-yielding oil production platform. In this review, we compare the oil biosynthetic pathways in seed and non-seed tissues. We describe how such knowledge, aided by recent -omics approaches, has paved the way for the engineering of vegetative tissues to generate elevated TAG levels in several plant species. While initial attempts predominantly targeted single genes, recent combinatorial metabolic engineering strategies have focused on the simultaneous optimization of oil synthesis, packaging and degradation pathways (i.e., ‘push, pull, package and protect’). This holistic approach has resulted in dramatic, seed-like TAG levels in vegetative tissues. With the first proof of concept hurdle addressed, new challenges and opportunities emerge including engineering fatty acid profile and translation into agronomic crops, extraction, and downstream processing to generate accessible and sustainable bioenergy.