2013 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, 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 developed for cellulosic and thermal bioenergy. In FY 2013, 8 transgenic sorghum lines, their parental line Tx 430, a resistant check SC 748-5, and susceptible checks BTx 623, ATx 623, and TAM 428 were evaluated in the greenhouse for resistance to Colletotrichum sublineolum, the causal agent of sorghum anthracnose. Several germplasm types including 11-6078 pZ-CYP98A1; 11-6138 pZP-CCR 1; 11-10239 pZP-Pal 1; and 11-6331 Myb 68 ZG 129-4-10a exhibited low amounts of lesions on the infected leaves. The results showed that these transgenic sorghum lines can reduce the ability of the anthracnose pathogen to cause infection. Work by this project, as it continues, will determine the effect on fungal pathogen infection by modified lignin content in host sorghum lines. In its totality, the work will guide ongoing research by others to develop new sorghum types for use in bioenergy production that are resistant to key insects and fungal pathogens, and that are thus more productive and profitable for U.S. farmers.