THE PLANT
CELL
WALL-ACE LAB
Wallace Lab
@ the University of Georgia CCRC
Current Research
1. Investigating the post-translational phospho-regulation of the plant Cellulose Synthase Complex (CSC):
​
In plants, cellulose is synthesized at the plasma membrane by large multimeric protein complexes known as Cellulose Synthase Complexes (CSCs). CSCs contain multiple non-redundant Cellulose Synthase A (CESA) proteins, which serve as the catalytic subunits of the CSC. Additionally, several “accessory subunits”, including Cellulose Synthase Interactive 1 (CSI1), the KORRIGAN1 (KOR1) beta-glucanase, and the Companion of Cellulose synthase (CC) proteins, have been shown to directly associate with the core CSC and modulate its function.
Large-scale phosphoproteomic surveys indicate that CSC protein components are phosphorylated at greater than 30 different phosphorylation sites throughout the complex subunits. Post-translational phosphorylation events are known to regulate many aspects of protein behavior, such as enzymatic activity, subcellular localization, protein stability, and protein-protein interaction networks. Therefore, the goal of the Wallace lab is to 1) identify the protein kinases that catalyze CSC phosphorylation, 2) understand the consequences of each CSC phosphorylation event, and 3) utilize this information to improve cellulose biosynthetic output in model and agronomically relevant biomass species.
2. Using rationally designed glycosylation inhibitors to probe cell wall polysaccharide function:
​
Cell wall polysaccharides critically influence basic plant cellular growth and differentiation processes, such as cell division, cell elongation, and the acquisition of cell shape. Therefore, the glycosyltransferases that catalyze cell wall polysaccharide biosynthesis can be difficult to investigate genetically because disruption of these genes often leads to gametophytic lethality. We and other labs have demonstrated that synthetic monosaccharide analogs, such as alkynl or azido sugars compatible with click chemistry, can be directly incorporated into cell wall polysaccharides to facilitate glycan imaging. Additionally, fluorinated monosaccharide analogs are emerging as a new class of cell wall polysaccharide biosynthetic inhibitor.
​
We are currently utilizing fluorinated sugars and forward genetics to identify new components of the plant cell wall polysaccharide biosynthetic machinery and of plant cell wall integrity sensing pathways.
3. Investigating the function of the putative protein O-fucosyltransferase family in Arabidopsis:
​
Protein O-fucosyltransferases (POFTs) are important regulators of cell adhesion and cell-cell communication in metazoans. These enzymes utilize GDP-Fuc as a sugar nucleotide donor and transfer fucose onto Serine and Threonine residues in target proteins. The Arabidopsis genome contains nearly 40 genes that are annotated as putative POFTs, yet their precise biochemical functions remain enigmatic. Several other groups have demonstrated that plant POFT-like genes play a role in cell adhesion and cell wall polysaccharide deposition. We recently characterized an additional POFT-like protein that we refer to as Arabidopsis O-fucosylTransferase 1 (AtOFT1). This gene exhibits very similar primary sequence functional motifs to confirmed metazoan POFTs, and plays a unique role in pollen tube penetration through the female pistil during fertilization.
​
Our current goals in this area are to 1) develop a better functional understanding of POFT-like genes and the roles that they play during double fertilization, 2) identify the substrates and target proteins of POFT-like proteins, and 3) understand how these proteins directly or indirectly regulate plant cell adhesion.
4. Investigating glycosyltransferases implicated in cellwall pectic polysaccharide biosynthesis:
​
Pectin is a major component of the plant cell wall and makes up about one third of the primary cell wall. Despite the abundance of this polysaccharide and its importance in providing strength to the wall, its complexity has made it abundantly difficult to study. Previous work in our lab has been done to investigate a family of putative protein O-fucosyltransferases in Arabidopsis thaliana. Thus far, we have determined that several of these proteins have been misannotated and functionally act as O-rhamnosyltransferases among other GT activities that are not the canonical POFUT1 fucosylation event. These rhamnosyltransferases have been determined to be essential in pectic rhamnogalacturonan-I biosynthesis by working with other enzymes to build the pectic backbone.
​
​