1a.Objectives (from AD-416):
To determine which alterations to the lignin biosynthetic pathway affect resistance to fungal pathogens and insect herbivory in sorghum, thereby allowing for deployment of bioenergy sorghum containing the desired lignin modifications without increasing biotic pressures. To discover the metabolic and signaling changes that affect plant-biotic interactions.
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.
1b.Approach (from AD-416):
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.
The goal of this project is to determine the impacts of lignin modification on fungal pathogen and insect interactions in sorghum for cellulosic and thermal bioenergy. Lignin is a complex chemical compound that is an integral component of the cell walls of plants. In FY 2012, 17 sorghum lines judged to have bioenergy potential were evaluated for resistance against the anthracnose pathogen (Colletotrichum sublineolum) in greenhouses and fields in Texas and in Puerto Rico. All the lines were susceptible to the anthracnose pathogen; however, variation in the percentage of foliar area infected was observed among the lines, indicating that some genetic diversity with respect to anthracnose susceptibility/resistance was likely present in the lines tested. Work by this project, as it continues, will determine the relationship of reduced lignin in the host to fungal pathogen infection. The work will ultimately facilitate identification/development of sorghum types appropriate for exploitation as cellulosic bioenergy feedstocks.