1a.Objectives (from AD-416):
To develop transgenic lines overexpressing phenylpropanoid biosynthetic enzymes.
In year 1, we will assemble T-DNA transformation vectors to transgenic overexpression of phenylpropanoid metabolic genes in sorghum. In years 2 and 3, complete the transformation and characterization of these transgenic lines. This objective will provide transgenic lines that over-express all 10 gene products in sorghum monolignol biosynthesis for specific objectives 2-5.
1b.Approach (from AD-416):
To increase carbon flux through the phenylpropanoid pathway, we will introduce seven constitutive expression cassettes under control of the maize ubiquitin promoter. We will constitutively express the genes encoding 7 enzymes in the sorghum monolignol pathway: cinnamate 4-hydroxylase, 4-coumarate-CoA ligase, hydroxycinnamoyl CoA:shikimate/quinate transferase, caffeoyl CoA O-methyltransferase, ferulate 5-hydroxylase, caffeic acid O-methyltransferase and cinnamyl alcohol dehydrogenase in RTx430 sorghum. Agrobacterium-mediated transformation will be used coupled to npt II selectable marker. For each transgenic cassette a minimum of 10 independent events will be generated.
Seven transgenes whose products are involved in the synthesis of the cell wall polymer lignin were transformed in sorghum. Two to three elite transformed lines for each transgene were selected based on the highest accumulation of the transgenic gene product. These elite lines are being exposed to key fungal pathogens and insect pests of sorghum to determine whether these approaches to engineer lignin synthesis impact susceptibility to these pests and pathogens. The knowledge gained from this research will be valuable in the development and deployment of sorghum and other grasses, because lignin is a major research target for bioenergy crop improvement.