Ph.D. 2002, Stanford University
Synthesis & Regulation of Grass Cell Walls
Grasses have diverged from other flowering plants in terms of cell wall content and patterning. The Bartley Lab uses molecular genetics, systems biology, and biochemistry to develop and test hypotheses of grass-diverged aspects of cell wall content biosynthesis and regulation.
Cell Wall Synthesis
Research on grass cell wall synthesis in the Bartley Lab is focused on understanding the function of a grass diverged clade of so-called BAHD acyltransferases that appear to function in incorporating hydroxycinnamic acids into grass cell walls. Hydroxycinnamic acids are a type of aromatic compound called phenylpropanoids (Figure A). Hydroxycinnamates can be linked to lignin, xylan, and possibly other polymers in grass cell walls. These linkages are not abundant in other classes of plants and their function in grasses is only now being tested directly as mutants with altered hydoxycinnamates become available. What is known is that ferulic acid attachment on xylan correlates with an increase in cell wall cross-linking, and is associated with reduced suitability for biofuel production via biochemical methods. In addition to examining genes and the enzymes that they encode for function in this process, the Bartley Lab is interested in how these modifications affect interactions with fungal symbionts and pathogens. To date, we have reported that the rice acyltransferase, AT10, functions in the incorporation of p-coumarate onto arabinoxylan (Bartley et al. 2013). Studies of At10 and related genes is on-going.
Figure A. Hydroxycinnamtes are abundant cell wall modifications in grass cell walls that may effect suitability for biofuels and aspects of grass biology. Image: (Bartley, 2013).
Cell Wall Regulation
Virtually every plant cell is surrounded by its own cell wall, which determines the shape of that cell and is often related to the cell’s function. The walls of cells in different organs (e.g., stems vs. leaves) have different compositions and change as organs grow and mature. For example, cell walls in stems function to provide structural support to the plant and facilitate passage of water and nutrients. Still, when a cell in the stem first forms, its cell wall must be flexible to allow the stem to elongate and grow. When growth ceases, the walls of stems then thicken and become stronger. This project seeks to understand the regulation of cell wall development, especially the gene products that control secondary cell wall growth.
Genetics & Genomics of Switchgrass and Other Grasses for Biofuels and Carbon Storage
Why switchgrass? To achieve the DOE goal of 30% production of transportation fuel from alternative sources by 2030, bioenergy crops need to be improved for large-scale implementation of biofuel production from lignocellulosic material. Cultivated grasses are the most abundant sustainable class of biomass that can be produced in the U.S. (~57%). Switchgrass is a particularly attractive native species for development as a biofuel crop given that largely unimproved varieties exhibit large biomass (up to 36.7 Mg/ha) and marked stress tolerance. The latter is especially important in the Southern and Central Plains, including Oklahoma, where drought is common and food crop production relatively marginal. Key criteria for switchgrass selection and engineering are biomass yield per area and biomass quality, which refers to the impact of cell wall content and structure on the efficiency of conversion to fuel.
- Population genetics and transcriptomics in switchgrass to identify genes associated with superior cell wall quality and switchgrass genotypes that convert to biofuels more efficiently.
- Identification of the cell wall components that correlate with improved thermal degradation products that might lead to the improvement of bio-oil composition.
- Switchgrass resequencing.
- In addition to being a potential source of chemical energy, cell walls are also the major source of soil carbon. In collaboration with ecologist Dr. Lara Souza (link)
Cell Wall Remodeling During Lateral Root Formation
Various plant organs and cells must grow through extant tissues to function, requiring remodeling of the normally tough and contiguous cell walls that surround each plant cell. For example, lateral roots (LRs) emerge past 10 cell layers from deep within the root cortex. This project will illuminate the molecular mechanisms by which plants form new lateral organs during development and in response to stress.
This understanding will allow optimization of cereal plant root branching toward improving drought tolerance and provide insight into how plants rearrange their own cell walls, a process related to next-generation biofuel production. More specifically, the project will address the hypothesis that cell shape and wall remodeling is driven by transcription factors that are expressed in cells overlying the emerging lateral roots. To test this, the project will develop a quantitative spatiotemporal model of the changes to cell shape and cell wall content that occur during rice lateral root emergence using various light microscopy and immunofluorescence with cell wall epitope antibodies.
The project will distinguish between genes required for new cell wall synthesis in the LR primordium and those functioning in cell wall remodeling and separation using quantitative reverse transcription and RNA Seq analysis methods. Plans are to follow up this work by testing for activation of the expression of cell wall remodeling genes by identified transcription factors in transient assays and via creation and analysis of transcription factor mutants.