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Departments: Biomass & Bioenergy

Ian Wallace


Ian Wallace received his B.S. and Ph.D. in Biochemistry, both from the University of Tennessee, Knoxville. He graduated in 2008. Wallace has also been a Postdoctoral Research Associate at the Energy Biosciences Institute, UC Berkeley.  Before his upcoming position with the CCRC, he was faculty at the University of Nevada, Reno for nine years, becoming Associate Professor and Graduate Program Director for their Biochemistry and Molecular Biology Department.

Research Interests:

Wallace studies the biosynthesis, deposition, and regulation occurring in plant cell walls, particularly the regulation of cellulose synthase catalytic subunits. He also researches plant protein kinase and phosphorylation-based signal transduction. Furthermore, he is interested in lignocellulosic biofuel and forage crop applications that come from understanding and manipulating plant cell wall digestibility.

More interests include the following:

  • Hormonal regulation of plant metabolism and development
  • Pollen-pistil interaction signalling
  • Antimicrobial drug discovery and mechanistic analysis


Maria Peña

Short Biography:

Dr. Peña received her B.S. in Biology in 1989 and her M.S. and Ph.D. degrees in Plant Science in 1994 and 1996, respectively, from the University of Santiago de Compostela (Spain). Prior to joining the CCRC in 2003, she was a Postdoctoral Fellow from 1998 to 2002 in the Department of Botany and Plant Pathology of Purdue University (IN). Currently, Dr. Peña is an Associate Research Scientist at the CCRC and funded investigator of the DOE Center for Bioenergy Innovation (CBI).

Dr. Peña has over 60 full publications, 1 book charter and 1 patent.


Research Interests:

Dr. Peña’s research focuses on several topics related to plant cell walls including i) synthesis, structure, and biological function of cell wall polysaccharides, ii) plant biomass deconstruction by microorganisms, and iii) production of plant cell wall-derived biomaterials. This research involves the application of advance mass spectrometry and NMR spectroscopy techniques for the determination of polysaccharide structure, functional characterization of carbohydrate-active enzymes and protein-carbohydrate interactions.


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Breeanna Urbanowicz

Short Biography:
Dr. Urbanowicz received her B.S. in Biology in 2001 from Purdue University and her Ph.D. in 2008 from Cornell University. Prior to her junior faculty position at the Complex Carbohydrate Research Center, Dr. Urbanowicz was a Postdoctoral Fellow (2008-2013) in the Department of Biochemistry and Molecular Biology at the University of Georgia.

Research Interests:
Biological molecules, including proteins, polysaccharides, and nucleic acids, are assembled to create complex structures with biochemical and biomechanical properties that are greater than the sum of their parts. My current research focuses on understanding the structure and function of plant carbohydrate active enzymes involved in polysaccharide biosynthesis and modification. Plant cell walls are complex macrostructures comprised of cellulose, hemicellulose, and pectins, together with lesser amounts of protein and phenolic molecules. These components assemble and interact with one another to produce dynamic structures with many capabilities, including providing mechanical support to plant structures and determining the size and shape of plant cells.
The research of my group focuses on understanding the integral steps in the molecular pathways used by plants to synthesize complex polysaccharides. A key area of interest is development of methods to express and analyze recombinant plant enzymes, which has allowed us to investigate plant biochemical pathways in vitro. We have now generated a large collection of recombinant enzymes that are able to catalyze highly specific, covalent modifications of polysaccharides, which we utilize as nature-inspired molecular tools for targeted functionalization and labeling of glycopolymers that greatly expand our toolkit for producing glycopolymer-based products with valuable properties.

High throughput expression of plant biocatalysts. In collaboration with Kelley Moremen at the CCRC, we have designed and evaluated over 75 constructs for heterologous expression in HEK293 cells encoding plant glycosyltransferases (GTs) from diverse families in addition to both polysaccharide O-methyltransferases (O-MTs) and O-acetyltransferases (O-AcTs). Assessment of these constructs for both protein expression levels and retention of in vitro activity determined that this is a robust heterologous expression system for plant derived enzymes. We have applied this system to the in vitro synthesis of decorated hemicellulosic polymers, resulting in the first proof-of-concept generation of enzymatically synthesized, high degree of polymerization (DP), substituted plant polysaccharides in vitro (Urbanowicz et al., 2014).

Polysaccharide Methyltransferases. We have shown that Arabidopsis GXMT1 encodes a glucuronoxylan (GX)-specific 4-O-methyltransferase responsible for methylating 75% of the GlcA residues in GX isolated from mature Arabidopsis inflorescence stems. Reduced methylation of GX in gxmt1-1 plants is correlated with altered lignin composition and increased release of GX by mild hydrothermal pretreatment (Urbanowicz et al., 2012). The ability to selectively manipulate polysaccharide O-methylation may provide new opportunities to modulate biopolymer interactions in the plant cell wall. We are currently investigating the role of other members in this family on polysaccharide methyletherfication.

Investigating the mechanism of polysaccharide O-acetylation. Despite the high degree of O-acetyl substituents found in plant glycopolymers, the biochemical and mechanisms of polysaccharide O-acetylation employed by plants are still lacking. An unsolved question is the source of the acetyl group used by acetyltransferases. We have developed robust methods to biochemically analyze O-acetyltransferases and are applying these techniques to investigate the molecular details of polysaccharide methylation.

Debra Mohnen

Short Biography:

Debra Mohnen is a Distinguished Research Professor at the Complex Carbohydrate Research Center, as well as the Department of Biochemistry and Molecular Biology at the University of Georgia. Dr. Mohnen received her B.A. in Biology (1979) at Lawrence University, Appleton, WI and her M.S. in Botany (1981) and Ph.D. in Plant Biology (1985) from the University of Illinois, Urbana, IL, with research conducted at the Friedrich Miescher Institute, Basel, Switzerland. Prior to joining the CCRC, she carried out five years of postdoctoral research at the CCRC and USDA, ARS, Russell Research Center in Athens, Georgia. Dr. Mohnen has served as Chair of the Plant Cell Wall Gordon Conference and since 1990 has lead a research team focusing on pectin synthesis, structure and function, with emphasis on the role of pectin glycan domains in wall architecture and plant cell growth. In 2008 she was awarded the Bruce Stone Award for research in pectin synthesis and elected as a fellow of the American Association for the Advancement of Science in 2013. Her research on synthesis of the two pectin glycan backbones, homogalacturonan and rhamnogalacturonan, led to the discovery of the GAUT and RGGAT families of glycosyltransferases and the recognition that pectin exists and functions as a family of glycan domains in cell wall heteroglycans and glycoconjugates. Since 2007 part of her research has been directed at improving plant biomass yield, sustainability and composition for the production of biofuel and biomaterials. As Focus Area Lead of Plant Biomass Formation and Modification in the DOE-funded BioEnergy Science Center (BESC), she directed a team of researchers aimed at understanding and overcoming biomass recalcitrance to deconstruction and since 2017 she serves as Research Domain Lead for Integrative Analysis and Understanding in the Center for Bioenergy Innovation (CBI). Her current efforts are focused on a new model for pectin function in cell expansion and wall structure. 

Research Interests:
Dr. Mohnen’s research focuses on the biosynthesis, function and structure of plant cell wall polysaccharides and glycoconjugates, with emphasis on pectin, matrix polysaccharides and wall proteoglycans.

The research goals include:

*Understanding the structure, biosynthesis and function of wall polymers that contain pectic glycans.

*Improving plant growth and development, and the use and conversion of plant cell wall biomass to biofuels and bioproducts, through modification of wall structure and synthesis.

*Reevaluation of plant cell wall models based on recently identified wall matrix glycan-containing proteoglycan structures, and glycosyltransferase gene family member functionalities, that are inconsistent with current wall models.

The research includes biochemical, chemical, molecular genetic and genomic methods and use of both model systems (e.g. Arabidopsis and rice) and biomass feedstock (e.g. Populus and switchgrass).

Michael G Hahn

Short Biography:
Dr. Hahn received a B.S. in chemistry and a B.A. in Independent Studies in 1974 from the University of Oregon and his Ph.D. in biochemistry in 1981 from the University of Colorado. A postdoctoral research associate appointment at the University of Wisconsin-Madison in plant pathology followed, after which Dr. Hahn went to the Albert-Ludwigs-Universiät (Freiburg, Germany) with the support of an Alexander-von-Humboldt stipend. Following another postdoctoral research associate appointment at the Salk Institute (San Diego, CA), Dr. Hahn joined the CCRC in July 1986. Full publications: 77.

Research Interests:
Our laboratory studies the cell biology and biosynthesis of plant cell walls. Plant cell walls play major roles in the biology of plants. Examples of these roles include controlling the growth and shape of plant cells, tissues, organs, and ultimately the entire plant, regulating the movement of nutrients and signals within the apoplast and toward the plasma membrane, serving as the first line of defense against pathogens and environmental stresses, and acting as a source of signaling molecules important in plant development and defense. Plant cell walls are also the principal component of plant biomass, which has become a focal point in the search for alternative and renewable sources of energy (biofuels).
We are pursuing two broad research goals:

(A) We are investigating plant cell wall biosynthesis by looking at two families of genes, primarily in Arabidopsis, thought to encode glycosyltransferases involved in plant cell wall glycan biosynthesis: 1) GAlacturonosylTransferase-Like (GATL) proteins thought to be involved in pectin biosynthesis; 2) FUcosylTransferase (FUT) proteins thought to add fucosyl residues to diverse plant cell wall glycans.

(B) We have developed a large and diverse library of monoclonal antibodies against plant cell wall glycans. These antibodies are being used to determine the locations of diverse cell wall carbohydrate structures (epitopes) in Arabidopsis, switchgrass and poplar. These antibodies are also proving useful for plant cell wall mutant characterization studies, and for quantitating glycans in cell wall extracts.

Our laboratory utilizes a broad range of experimental approaches in these studies, including molecular genetic, biochemical, immunological and microscopic techniques.

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Alan Darvill

Short Biography:
Alan Darvill received his B.S. in plant biology in 1973 from Wolverhampton Polytechnic (England) and his Ph.D. in plant physiology in 1976 from the Aberystwyth (Wales). He founded the CCRC with Dr. Peter Albersheim in September 1985. Dr. Darvill is Director Emeritus of the CCRC, former Director of the Department of Energy (DOE)-funded Center for Plant and Microbial Complex Carbohydrates, and was University of Georgia lead in the DOE-funded BioEnergy Science Center. He was elected chairman for 1994-95 of the Carbohydrate Division of the American Chemical Society, and was appointed a member in 1993 and chairman in 1996 of the Martin Gibbs Medal Committee of the American Society of Plant Physiologists. He served on the editorial boards of Glycobiology and of the Plant Journal for Cell and Molecular Biology. Dr. Darvill received the Outstanding Faculty Award of the UGA Chapter of the Golden Key National Honor Society in 1995. In 2003, Dr. Darvill was appointed Regents Professor of Biochemistry and Molecular Biology and Senior Faculty Fellow. In 2008, he was appointed to the University of Georgia Research Foundation Board, and in 2010 was named Fellow of the American Association for the Advancement of Science. Full publications: 220.

Research Interests:
Characterization of the non-cellulosic polysaccharides that constitute the primary cell walls of plants has been a major research goal of our laboratory for many years. We have emphasized the structural studies of five major non-cellulosic polysaccharides, namely, the pectic polysaccharides rhamnogalacturonan I (RG-I), rhamnogalacturonan II (RG-II), and homogalacturonan, and the hemicellulosic polysaccharides xyloglucan and arabinoxylan. We have characterized the structures of these polysaccharides isolated from angiosperm and gymnosperm cell walls. We have come to realize that these polysaccharides are the predominant non-cellulosic polysaccharides of cell walls. These polysaccharides, although varying in quantity in the cell walls of angiosperms and gymnosperms, are structurally conserved, indicating their importance in primary cell wall structure and function.

These cell wall, non-cellulosic polysaccharides represent a group of carbohydrates with considerable structural complexity that offer a major challenge to those wishing to decipher their structures. RG-II, for example, is probably the most structurally complex polysaccharide so far isolated from nature. RG-II was first discovered to be a component of the primary cell walls of plants by our laboratory in 1978 and has now been found in the walls of angiosperms, gymnosperms, lycophytes, and pteridophytes. RG-II is a small polysaccharide consisting of approximately 30 glycosyl residues. However, this polysaccharide contains at least 12 different glycosyl residues linked together in over 20 different glycosyl linkages. RG-II is characterized by several unusual sugar components including 2-O-methyl fucose, 2-O-methyl xylose, apiose, 3-C-carboxy 5-deoxy-L-xylose (aceric acid), 3-deoxy-D-manno-2-octulosonic acid (KDO), and 3-deoxy-D-lyxo-2-heptulosaric acid (DHA). Both aceric acid and DHA have been found in no natural source other than RG-II.

We have characterized oligosaccharide fragments of RG-II that contain 28 of the possible 30 glycosyl residues of this pectic polysaccharide. We have obtained evidence that the backbone of RG-II consists of seven a-1,4-linked galactosyluronic acid residues to which two disaccharide, one heptasaccharide, and one octasaccharide side chains are attached. These side chains are attached to the backbone via the acid labile ketosidic and glycosidic linkages of KDO, DHA, and apiose. The demonstration that RG-II exists in primary walls as a dimer that is covalently cross-linked by a borate diester was a major advance in our studies of this polysaccharide. Dimer formation results in the cross-linking of the two homogalacturonan chains upon which the RG-II molecules are constructed and is required for the formation of a three dimensional pectic network “in muro” (Annual Review of Plant Biology, 2004, 55:109-139).

Research in our laboratory continues to emphasize the structural characterization of the non-cellulosic polysaccharides of cell walls. The availability of cell wall mutants is assisting us in these structural studies. Structural analysis is accomplished by release of polysaccharides from cell walls and generation of defined polysaccharide fragments with purified enzymes or chemical treatments, chromatographic purification of the oligo- and polysaccharides, chemical structural characterization techniques, and a combination of several analytical techniques including gas-liquid chromatography, liquid chromatography, gas-liquid chromatography-mass spectrometry, liquid chromatography-mass spectrometry, MALDI-TOF mass spectrometry, and 1H- and 13C-NMR spectroscopy.

We are also collaborating with Dr. Michael Hahn in the production of monoclonal antibodies to cell wall polysaccharides and the oligosaccharides derived from these polysaccharides. These antibodies will be used in both purification of oligosaccharides and, more importantly, to begin to decipher the arrangement and location of the polysaccharides within the primary cell wall using monoclonal labeling of specific epitopes on the wall polysaccharides.