SCAN: Association of pectin- and hemicellulose- gene expression with secondary growth in Eucalyptus

Abstract
Wood is a major source of land biomass. It is a valuable resource, not only for pulp and paper production, but also as a renewable source of energy and as a sink for excess atmospheric CO2. Wood quality is ultimately related to the morphology and biophysical properties of the xylem cell wall. Differences in wood structure and chemistry, like fiber length, cell wall thickness, cellulose and lignin content, have effects on the quality and economic value of wood.
Xylogenesis (wood formation) involves cell division and elongation, growth restriction, thickening of the cell walls and programmed cell death, in a co-ordinated process involving synthesis, integration and selective modifications of the cell wall matrix by a number of polysaccharide-modifying enzymes. Genes that intervene early in wood formation may significantly influence the characteristics of the wood formed. Cellulose and lignin biosynthesis have been extensively studied at the molecular level, but few studies have focused on wall-loosening and the extensive modifications of matrix components that occur during xylogenesis.
To date, the study of wood formation in trees has been conducted mainly using Populus as a model species. However, Eucalyptus is the most important commercial temperate hardwood species in the world. It possesses rapid growth rate and has a high quality wood fiber suited to pulp and paper making.
Here we report the identification of a set of Eucalyptus candidate cell wall-modifying genes acting on the cellulose-hemicellulose network and on the pectic polysaccharides. A total of 38 cDNAs from 9 families (4 xyloglucan endotransglycosylase/hydrolases, 3 endo-1,4-b-glucanases, 6 a-expansins, 2 b-expansins, 1 expansin-like, 3 mannan-hydrolases, 2 xylanases, 1 pectate lyase, 5 polygalacturonases, 7 pectin methylesterases, and 4 pectin acetylesterases), representing new entries to the GenBank databases were cloned from 1-year old trees by homology-based-cloning of candidate families. The pattern of mRNA accumulation of the each cDNA was assessed in histologically characterised wood-forming tissues. Distinct, gene-specific, expression patterns were obtained for each gene, which allowed the identification of genes preferentially expressed in stem regions undergoing secondary growth.
Wood is a highly heterogeneous material, and distinct differences occur not also between species and between trees, but also within the same individual tree. Therefore, differences in gene expression were also investigated in distincts xylogenic programmes like tension/opposite wood formation and in juvenile/mature wood. The results allow us to extend our discussion about the possible role of each gene and allow associating wood formation with the expression of pectin- and hemicellulose modifying genes.
Current work is now focused on the functional characterisation of selected genes, which may influence cellulose assembly. Four XTHs were produced heterologously and their substrate and mode of action is being characterized. The role of a KORRIGAN-like endoglucanase, putatively involved in cellulose biosynthesis, is being investigated using Agrobacterium-mediated transformation of Arabidopsis KORRIGAN-supressed mutants. The results obtained so far will be presented.

Short CV
2005 – Post-Doctoral Researcher, Plant Cell Wall Group, Instituto de Tecnologia
Química e Biológica, Oeiras.
2000-2006 – PhD in Agronomic Engineering, Instituto Superior de Agronomia,
Lisboa.
1997-2000 – Research Fellowship, Estação Nacional de Fruticultura Vieira
Natividade, Alcobaça / Universidade do Algarve, Faro / Instituto Superior de
Agronomia, Lisboa.
1996 - Degree in Agronomic Engineering (Plant Breeding), Instituto Superior de
Agronomia, Lisboa.