CHEWING THE FAT: MODIFYING FATTY ACID BIOSYNTHESIS IN Lolium perenne

¹ AgResearch, Grasslands Research Centre, Tennent Drive, Private Bag 11008, Palmerston North, New Zealand

² Agriculture Victoria, La Trobe University, Bundoora, Victoria, 3083, Australia

Grazed pasture is the primary feed source for animal production in New Zealand because its low-cost provides a comparative advantage to this export-based industry. However, the nutritive value of pasture is highly variable when compared to concentrate feeds, and restricted energy intake is the main limitation to productivity in pasture-based systems. Combining AgResearch's elite forage germplasm resources with functional genomics allows us to take a novel approach to rectify this. We propose to over express acyl-CoA:diacylglycerol acyltransferase (DGAT) in the leaves of ryegrass plants containing elevated ratios of omega-3 fatty acids. This would not only increase the energy content of the vegetative portions of the plant, by producing triglycerides, but would also increase the content of lipids with health promoting properties. We are currently cloning the endogenous DGAT gene from ryegrass and as a proof-of-concept we have placed the A. thaliana DGAT cDNA under the control of a constitutive promoter into ryegrass. In separate proof-of-concept experiments, involving feeding trials, we found that supplementing triglyceride to sheep at pasture resulted in greatly enhanced efficiency of conversion of dry matter intake to lamb carcass weight and improved the lipid composition in the meat. To find plants with elevated omega-3 fatty acids both vegetative and non-vegetative samples collected over the course of a year are being analysed by FAMES GC-MS. To complement this we have obtained full length cDNA clones of a number of important fatty acid desaturases. We will present our progress in a number of the areas described.