| Staff Professor Tony Bacic (CI) Dr Carolyn Schultz (CI) (University of Adelaide) |
| Postgraduate Students Mr Umesh Nagasandra (University of Adelaide) Ms Yongmei Qu Mr Joel Youl |
This is a collaboration with Dr Carolyn Schultz (School of Agriculture & Wine, University of Adelaide) and is funded by an ARC grant (DP0343454).
Arabinogalactan-proteins (AGPs), the major constituent of gum arabic, have been used for centuries as emulsifiers and stabilizing agents. They are also abundant cell surface proteoglycans consisting of >90% carbohydrate linked to a minor (<10%) protein backbone. In many cases a glycosylphosphatidylinositol (GPI) anchor attaches then to the outer leaflet of the plasma membrane (see Figure). Despite their abundance and industrial utility, the in vivo function(s) of AGPs remains unknown. The broad objective of our program is to define the molecular mechanisms of AGP function using Arabidopsis thaliana as a model system.
Bioinformatics
We developed custom software in order to identify AGPs from the Arabidopsis genome based on the biased amino acid composition of AGP backbones (AGPs are rich in Pro, Ala, Ser, and Thr). More than 50 different genes encoding AGP protein backbones have been identified and these are classified into several sub-groups.
These include:
Molecular Biology
Most single gene Arabidopsis AGP mutant and transgenic plants do not show phenotypes under standard glasshouse conditions. We are challenging them under various conditions (e.g. hormones, pathogens) based on data from microarray and other experiments.
We are also crossing lines to make multiple mutants where data suggests that they are from the same functional class and/or expressed under similar conditions.
We are also using multiple RNAi for reducing the expression of several genes in a single plant. We have generated a construction vector where several independent RNAi modules can be inserted using GatewayTM. We have also generated several AGP native promoter::GFP/GUS lines to visualise expression of the genes.
Biosynthesis / Biochemistry
We are also focussing on the biosynthesis of AGPs. AGPs are extensively modified post-translationally. We have confirmed that AG-peptides are bona fide AGPs in that they precipitate with single Yariv reagent. using MALDI-TOF MS/MS sequencing we have also determined the precise cleavage site for GPI-anchor additions for 8/12 AG-peptides. Protein sequencing of AG-peptides has also revealed that, in addition to the expected Ala-Pro, Ser-Pro motifs, the Gly-Pro motif can be hydroxylated in vivo. The knowledge of the post-translational modification of the protein backbone assist in developing and refining prediction tools for the primary structure of AGPs.
The other significant modification of AGPs is the addition of AG polysaccharides. A family of Type II glycosyltransferases have been identified by bioinformatic analysis of the Arabidopsis genome and using the CAZY database. We are using a combination of molecular and biochemical approaches to test whether the genes are responsible for the synthesis of the ß(1-3) galactan backbone of AGPs.
The AGP research program benefits from an active collaboration with a group at INRA, Versailles, France (Professor Herman Hofte and Dr Gregory Mouille) to investigate changes to cell wall structures using Fourier Transform Infrared (FTIR) microspectroscopy. An understanding of the in planta function of AGPs has the potential to benefit both industrial and agricultural sectors of the economy.
Gaspar YM, Nam J, Schultz CJ, Lee L-Y, Gilson PR, Gelvin SB, Bacic A (2004) Reduced expression of an Arabidopsis lysine-rich arabinogalactan-protein, AtAGP17, results in a decreased efficiency of Agrobacterium transformation. Plant Physiology First published on July 30, 2004; 10.1104/pp.104.045542.
Schultz C, Ferguson, Bacic A (2004) Post-translational modifications of arabinogalactan-peptides of Arabidopsis thaliana: ER and GPI-anchor signal cleavage sites and hydroxylation of proline. Journal of Biological Chemistry (in press).
Eisenhaber BJ, Wildpaner M, Schultz CJ, Borner GHH, Dupree P, Eisenhaber F (2003) Glycosylphosphatidylinositol lipid anchoring of plant proteins. Sensitive prediction from sequence- and genome-wide studies for Arabidopsis and rice. Plant Physiology 133:1691-1701.
Johnson K, Jones B, Schultz CJ, Bacic A (2003) Non-enzymic cell wall (glyco)proteins. In: The Plant Cell Wall, J Rose (ed), Blackwell Publishing, UK, ch 4, pp. 111-154.
Johnson KL, Jones BJ, Bacic A, Schultz CJ (2003) The fasciclin-like arabinogalactan proteins of Arabidopsis. A multigene family of putative cell adhesion molecules. Plant Physiology 133:1911-25.
Schultz CJ, Rumsewicz MP, Johnson KL, Jones BJ, Gaspar YM, Bacic A (2002) Using genomic resources to guide research directions. The arabinogalactan protein gene family as a test case. Plant Physiology 129:1448-63.
Gaspar Y, Johnson KL, McKenna JA, Bacic A, Schultz CJ (2001) The complex structures of arabinogalactan-proteins and the journey towards understanding function. Plant Molecular Biology 47:161-76.
| Created: January 2004 by svgdesign.com.au |
| Last modified: July 29, 2005 |
| Authorised by: Prof. Antony Bacic & Assoc. Prof. Ed Newbigin |
| Access: Open |
| Copyright © 2004 The University of Melbourne. |
| Maintainer: Chris O'Brien, School of Botany |
