Researchers say plants of the future may be harvested for the oil produced in their leaves rather than just their seeds
CSIRO PhD student Kyle Reynolds is part of a team that has demonstrated that new leaf oils can be engineered to contain valuable medium-chain fatty acids.
PHOTO: Paul Jones
Australian scientists working in CSIRO’s Plant Oil Engineering group recently announced the development of game-changing technology that enables plants to produce oil in their leaves rather than just their seeds, an advance that may one day enhance the availability of non-fossil-fuel-based raw materials for the food, animal feed, industrial and energy industries.
Now, in a further development just published in Frontiers in Plant Science, they have used a relative of the tobacco plant (Nicotiana benthamiana) to demonstrate that these new leaf oils can be engineered to contain valuable medium-chain fatty acids.
Lead author Kyle Reynolds, a GRDC-supported PhD student working with the CSIRO team, says medium-chain fatty acids have a carbon backbone that is eight to 14 atoms long and are found in abundance in palm kernel oil and coconut palm oil.
“Vegetable oils containing medium-chain fatty acids are already used as an ingredient by various industries for the manufacture of human food, animal feed, cosmetics, lubricants, coatings and detergents, and as a source of renewable energy because these fatty acids are an ideal feedstock for biodiesel,” he says
“It is predicted that by 2020 worldwide production of vegetable oil will be required to increase by 30 per cent just to keep pace with food oil demand, with the increase likely to come in part from increases in arable land and placing further pressure on endangered habitats.”
As a consequence, Mr Reynolds says there is an urgent need to develop additional bio-based sources of the industrial medium-chain fatty acids to supplement the palm and coconut palm oils and help replace unsustainable and environmentally damaging petroleum-based oils. In an attempt to expand global vegetable oil production, laboratories across the world are investigating the production of oil in non-seed biomass, such as leaves.
One of Mr Reynolds’s supervisors, Professor Chris Blanchard, who is director of the Functional Grains Centre based at Wagga Wagga, New South Wales, says crops able to produce high levels of oil in their leaves could be a game-changer for agriculture in the future.
“As well as having plants that produce oil in their seeds, plants that can produce oil in their leaves potentially turns farming on its head,” Professor Blanchard says.
“At the moment we worry about frost and heat stress at flowering because these climatic conditions potentially lower seed production, but being able to produce oil in the leaves of plants means we wouldn’t have to wait for grain to develop before we harvest the biomass.”
The work is at the frontier of agricultural research and has a goal of a commercial releaseof plants with high oil content in their leaves in five to 10 years.
Dr Allan Green, research director of bioproducts at CSIRO Food and Nutrition, told the 2015 Grains Industry Conference that plant leaf cells were normally rich in starch and other sugars but contained less than one per cent oils.
However, the CSIRO team, of which Kyle Reynolds is a member, has shown they can be engineered to accumulate about 35 per cent oil, a level equivalent to seed oil, in their leaves (Figure 1).
Figure 1 Oil presence in high-oil plants compared with normal leaf cells. Micrographcs of leaf cells that have been coloured to highlight the dense packing of oil droplets (yellow in the high-oil plants (top), compared to their virtual absence in the normal leaf cells (below). White is used to show the normal starch bodies in leaves.
To encourage N. benthamiana (the model plant used for experimental studies) to produce oils rich in medium-chain fatty acids in its leaves, the researchers used genes responsible for controlling the assembly of these specific fatty acids within the coconut palm (Cocos nucifera), the camphor laurel (Cinnamomum camphora), the California Bay laurel (Umbellularia californica) and the Cigar Flower (Cuphea lanceolata) and combined them with the genes previously used to create oil-accumulating leaves.
The isolated genes were inserted into the genome of the model plant, using carrier DNA derived from a bacterial species (Agrobacterium tumefaciens
), which can transfer that DNA into plants when they are stressed or injured.
Mr Reynolds used a syringe to inject the oil-synthesis genes of interest into the model plant and left it for five days. He then analysed the leaves and discovered the genes from all the plants tested were able to encourage the accumulation of medium-chain fatty acids in the novel leaf oils.
Dr Green says tobacco (N. tabacum), a close relative of N. benthamiana, is already being explored by a number of groups as a possible biomass crop, and could be a logical first step in the commercial development of biomass oil crops on the global stage.
However, he says tobacco production in Australia for this purpose would face significant regulatory hurdles as the crop is now prohibited.
Dr Green says sorghum, sugarcane, lucerne and wheat are good alternatives, especially where leaf oil production can be combined with normal grain production to create dual-purpose crops.
“In this regard, long-season winter wheats are particularly interesting because they can be repeatedly cut for biomass during the growing season and still produce high grain yields at maturity,” he says.
While the technology is still a way off – and the commercialisation of such crops would need to be approved by the Office of the Gene Technology Regulator (OGTR) – Dr Green says that with further research, the oil produced from plant leaves could match the productivity levels of the oil palm industry.
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