Transcription Regulatory Circuits of Grass Cell Wall Biosynthesis

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The costs of degrading cellulosic biomass currently impede its widespread use as a competitive domestic renewable alternative to fossil fuels. A promising route to renewable liquid fuels is the conversion of various biomass sources by microbial organisms. The goal for this project is to develop a basic understanding of the genes that control biomass accumulation. This will enable our long-term goal of producing ecologically and economically sustainable sources of feedstocks for biofuels. The research specifically addresses the genes that regulate a key aspect of plant growth, which is the creation of cell walls. In specific cells the walls are very thick and it is these that account for the bulk of all plant biomass. Grasses include many of our most important food and forage crops including maize, wheat, rice, ryegrass, and tall fescue. Despite the importance of the plant cell wall for plant growth, our knowledge of the precise regulatory mechanisms that give rise to the coordinated synthesis of the wall polymers is limited. This is especially true of grasses. This project will provide interdisciplinary training in development, genetics, genomics, and biochemistry for at least two University of Massachusetts graduate students and facilitate an internship program with the National Technical Institute for the Deaf.This proposal aims at understanding the transcription networks that regulate secondary cell wall biosynthesis in grasses. The cell wall is a complex composite of polysaccharides, proteins, and lignin. Much of what is currently understood about the transcriptional regulation of cell wall biosynthesis is from the study of Arabidopsis thaliana xylem vessels and fibers, yet this understanding may not be generalizable across land plants. The cell walls of grasses, including domesticated cereals that provide the majority of human calories and the perennials under development as biofuel energy crops, differ significantly in morphology and composition from the eudicot A. thaliana. The research will explore the function of three Brachypodium distachyon transcription factors: GRASS NAC REPRESSOR OF FLOWERING (GNRF), WALL REGULATOR INTERACTING bHLH (WRIB), KNOTTED-LIKE HOMEOBOX OF BRACHYPODIUM DISTACHYON7 (KNOB7). The researchers hypothesize that these proteins regulate wall biosynthesis through protein-protein and protein-DNA interactions that make-up a system of feed forward and negative feedback loops that are influenced by external cues. Transcription factors will be characterized by using methods such as chromatin immunoprecipitation to determine the gene promoter targets of the proteins and the effect of binding on cell wall biosynthesis. Protein-protein interactions will be evaluated using co-immunoprecipitation. A possible role for photo and thermocycles in the function of cell wall regulation will be tested by measuring function under varying time course conditions in plants of different mutant backgrounds.