Improvement of Forage Quality by Downregulation of Maize O‐Methyltransferase

Abstract

Lignin is a complex, aromatic polymer that limits plant cell wall degradation by ruminants and reduces the nutritional value of forages. Genetic engineering, using an antisense strategy, offers the potential to modulate enzymes in the lignin biosynthetic pathway as a way to reduce lignin, thereby improving forage quality and animal performance. We investigated the effectiveness of expressing antisense sorghum O‐methyltransferase gene (omt) to downregulate maize OMT and reduce lignin. Constructs contained a sorghum omt coding region in the antisense orientation driven by the maize ubiquitin‐1 (Ubi) promoter (with the first intron and exon) along with bar, that confers glufosinate herbicide resistance, driven by the CaMV 35S promoter. Twenty‐eight T0 plants regenerated from 17 herbicide‐resistant callus lines from 13 independent bombardments expressed the brown midrib phenotype. O‐methyltransferase activity was significantly lower in T1 transgenics compared with controls, with some plants showing a 60% reduction. Those T1 transgenics with downregulated OMT averaged 20% less lignin in stems and 12% less lignin in leaves compared with controls. On a whole‐plant basis, lignin was reduced by an average of 17% with the greatest reduction being 31%. Digestibility was significantly improved in transgenic plants by 2% in leaves and 7% in stems. Mean whole‐plant digestibility increased from 72 to 76%. This research demonstrates that genetic engineering has the potential to improve forage grass digestibility. This could be important, especially in tropical forage species, which generally have lower quality than temperate species.