Improving the Protein Content and Digestibility of Grain Sorghum Using Gene Editing

Professor Ian Godwin’s invited presentation focused on the use of gene editing and genetic modification techniques to improve the protein content and digestibility of sorghum for use in poultry feed. Sorghum is used to produce a range of human food and beverages and is the main summer grain produced in Australia. Sorghum copes well with the unpredictable Australian climate (heat, droughts, floods). Cereals make up more than 60% of poultry feed and sorghum is an excellent feed ingredient for poultry. However, there is a lot of discussion about the grain quality of sorghum and Professor Godwin’s group has researched the breaking down of the starch:protein matrix in sorghum grain. Studies have investigated changing starch, protein, cellulose, lignin, lipid and sugars in sorghum grain but this paper focuses on the work conducted on protein using genomics to inform transgenic and editing approaches. An understanding and control of gene expression underlies the improvement of grain quality. White sorghum produces better results in poultry as it contains lower levels of the proteins kafirins which reduce the digestibility of sorghum. Alpha kafirins are nutritious whereas beta and gamma kafirins are poorly digestible and coat the periphery of the protein body.

Professor Godwin and his colleagues set out to increase the size of the sorghum grain and to produce grain with more protein and more digestible protein. Only the successful manipulations are discussed in this paper. Foldase knockout lines were developed which used changes in the way proteins fold to target protein bodies and G-proteins associated with grain size were manipulated. RNAi silencing was used to down-regulate G protein gamma-subunits. Knocking out GGC1 increased grain size, knocking out GGC2 increased seed size and number and knocking out GGC3 mostly increased seed number. In this way, the composition of the endosperm could be changed from being corneous and floury in the wild-type control to being mostly floury (foldase knockout) or mostly corneous (GS3 knockout). An important aspect of gene editing is that the product is not considered to be a GMO because the “edit” is indistinguishable from a natural mutation. To date, the research group has edited 27 genes in sorghum resulting in 134,217,728 genetic combinations. Of these, the GGC1 knockout produces a larger grain and the GGC3 knockout more grain per head. The C1R1 line produces 40% more grain (grain size unchanged) resulting in 24% more protein. The C1R5 line produces 36% more grain, 19% larger grain and 17% more protein. The P4 line produced 32% more grain, 5% larger grain and 21% more protein. The C3R1 line produced 60% more grain (grain size unchanged) and 13% more protein. Overall, the selected lines produced more protein per grain and more protein (up to 91%) per hectare. This manipulation broke the nexus between grain size and grain number and protein and resulted in improvements in both yield and quality.

Some of the lines developed were selected for use in broiler feeding trials. During the first year of the trials, there were 17 consecutive days of 35C heat during grain fill and it was discovered that the C3 lines were heat susceptible. For the year 2 trials, the GS3 KO (C1R5) and foldase KO lines 2 and 4 were selected for testing. Formulating the diets was a challenge. The overall findings were that higher protein led to lower digestibility and FCR, lower protein led to higher digestibility and FCR but higher protein with higher digestibility (the foldase knockouts) led to the best FCR. Improved FCR results in reduced feed costs per chicken because protein (usually imported soybean meal) is the most expensive part of the ration. ExpressEdit technology is currently being developed at University of Queensland to enable gene editing to be conducted more quickly.

Finally, Professor Godwin provided the details of his new book “Too Good to Eat” which is a popular science book on history and the next generation of GM and gene edited crops and foods. It was published by the Royal Society of Chemistry in February 2019 (https://pubs.rsc.org/en/content/ ebook/978-1-78801-085-6), available at Avid Reader and online at Blackwells, Booktopia and Amazon and other providers.