|Chapman, Kent -|
|Mullen, Robert -|
Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 6, 2013
Publication Date: May 1, 2013
Citation: Chapman, K.D., Dyer, J.M., Mullen, R.T. 2013. Why don’t plant leaves get fat? Plant Science. 207:128-134. Interpretive Summary: There is significant interest in developing sustainable, more environmentally friendly biofuels that can replace traditional fossil oil-based fuels, but the demand for biofuels is generally far greater than what traditional agriculture can deliver. While "second generation" biofuels such as cellulose-derived ethanol or algae-based biofuels have potential for greatly increasing the amount of biofuels produced, these approaches are proving to be technically challenging and expensive. As such, novel approaches and high risk/high return research is needed for a step-change in biofuel production. In this invited article, scientists from the University of North Texas, University of Guelph, and the ARS lab in Maricopa Arizona discuss new and emerging research strategies that aim to produce high amounts of energy-dense oils in the leaves and stems of plants. Oils are normally produced in the seeds of plants, but seeds account for a minor percentage of total plant biomass, which is instead dominated by leaves and stems. Thus, production of even modest amounts of oil in leaves and stems could significantly increase the amount of oil recovered from plants. In this article, the scientists highlight metabolic pathways and other molecular processes that might be engineered to further increase the amounts of oil produced in leaves. This information will be of greatest value to other scientists who are working on production of biofuels in plants, particularly those who are focused on producing oils in the leaves and stems of plants.
Technical Abstract: Recent pressures to obtain energy from plant biomass have encouraged new metabolic engineering strategies that focus on accumulating lipids in vegetative tissues at the expense of lignocellulose and/or other carbohydrates. There are at least three important factors that support this rationale. i) Lipids are more reduced than carbohydrates and so they have more energy per unit of mass. ii) Lipids are hydrophobic and thus take up less volume than hydrated carbohydrates on a mass basis for storage in tissues. iii) Lipids are more easily extracted and converted into useable biofuels than lignocellulosic-derived fuels, which require extensive fractionation, degradation and fermentation of plant tissues. However, while vegetative organs like leaves represent the majority of harvestable biomass and would be ideal for accumulation of lipids, they have evolved as "source" tissues that are highly specialized for carbohydrate synthesis and export and do not have a propensity to accumulate lipid. Here we describe some of the metabolic explanations for "why plant leaves don‘t get fat" and highlight strategies that are being taken (or might be taken) to divert the flow of photosynthetic carbon from sucrose, starch, lignocellulose, etc. toward lipid accumulation in non-seed, vegetative tissues for bioenergy applications.