Location: Grain, Forage, and Bioenergy Research2011 Annual Report
1a. Objectives (from AD-416)
To determine which alterations to the lignin biosynthetic pathway affect resistance to fungal pathogens and insect herbivory in sorghum, and thereby allowing for deployment of bioenergy sorghum containing the desired lignin modifications without increasing biotic pressures. To discover the metabolic and signaling changes which affect plant-biotic interactions.
1b. Approach (from AD-416)
Specific Objectives: Examine effects of specific modifications to lignin biosynthesis through bmr loci or transgenic overexpression on feeding of greenbugs (phloem feeder), corn stalk borers and fall army worms (chewing insect). Examine the effects of these lignin modifications on the colonization of fungi causing foliar or stalk diseases, anthracnose (Colletotrichum sublineolum), stalk rot (Fusarium spp.) and charcoal rot (Macrophomina phaseolina). In the relevant lines, investigate the potential underlying mechanisms for significantly reduced insect feeding or fungal colonization relative to wild-type. The overall objective is to systematically link steps in lignin biosynthesis and accumulation of metabolites to changes in gene expression or defense signaling. Approach: To manipulate lignin, we will utilize 4 bmr loci and transgenic overexpression of 4 genes involved in monoliginol biosynthesis. The bmr loci all result in reduced lignin content, but have distinct effects on lignin composition and phenylpropanoid metabolism. We will overexpress genes encoding enzymes in monoliginol biosynthesis at critical branch points and a putative transcriptional regulator of lignin biosynthesis. Resistance to fungal pathogens will be assessed in the field and through greenhouse inoculation with fungal isolates containing GFP to examine fungal growth and extent of fungal penetration. Insect feeding studies will be performed using isolated leaves from staged plants at a fixed position. Phenolic metabolites will be analyzed by GC-MS in lines exhibiting fungal or insect resistance. Global gene expression will be analyzed using a newly developed Agilent sorghum genome microarray.
3. Progress Report
This new Agreement was initiated in February 2011. This series of experiments will examine how modifying a critical biochemical pathway, the synthesis of the cell wall polymer lignin, will affect the susceptibility of sorghum plants to insect pests and fungal diseases that cause significant crop losses. The plant transformation experiments to modify lignin content through biotechnology are underway. The experiments to measure the susceptibility of sorghum plants to insect pests and fungal pathogens are underway using the brown midrib 6 and 12 mutants, which are impaired in their ability to synthesize lignin. The knowledge gained from this research will be critical for deployment decisions of sorghum and other bioenergy grasses, because lignin is a major target for bioenergy crop improvement.