PI: Ewa Mellerowicz

Staff: Ajaya Biswal, postdoc; Christine Ratke, PhD student; Junko Takahashi, PhD student;

Background

Xylan is one of most abundant biopolymers on the Earth. Its main source is the wood of dicotyledonous species, where it is the main hemicellulose. Xylan is composed of beta-1,4-xylopyranose main chain with side chains of arabinose, acetyl and glucuronic acid, which may be or not methylesterified. It forms covalent linkages with lignin in cell wall and affects delignification process during pulping. Therefore, the amount and composition of xylan are good targets for genetic manipulation of trees.

Aims

The aims of this project are 1) to identify genes essential for xylan biosynthesis and modification in poplar and 2) to use well defined microbial genes to modify xylan in poplar for improved pulp characteristics.

Although several genes potentially involved in biosynthesis of xylan precursors are known in plants, the main backbone biosynthetic gene has not been yet reported. FRA8, a member of GT47, is a putative xylan glucuronyl transferase that has been recently described in Arabidopsis (Zhong et al. 2005). Recent identification of CAZY genes in poplar (Geisler-Lee et al. 2006) and the information on their expression during the normal wood formation (Schrader et al. 2004) as well as during the tension wood formation (Andersson-Gunnerås et al. 2006) allows us to pinpoint FRA8 homologue and other glycosyl transferases likely involved in the xylan biosynthesis as well as enzymes involved in xylan modification. Among the latter group, PttXYN10A, a xylan endohydrolase, has been found highly upregulated during the secondary wall formation in poplar (Aspeborg et al. 2005). The effects of suppression of this xylanase are currently being studied. Reverse genetic approach for poplar genes using both constitutive and inducible promoters, will be used to modify xylan. In addition to the poplar genes, well characterized microbial genes will be expressed in poplar to precisely target xylan composition.

References

• Andersson-Gunnerås S, Mellerowicz EJ, Love J, Segerman B, Ohmiya Y, Coutinho PM, Nilsson P, Henrissat B, Moritz T, Sundberg B (2006) Biosynthesis of cellulose-enriched tension wood in Populus: global analysis of transcripts and metabolites identifies biochemical and developmental regulators in secondary wall biosynthesis. Plant J 45: 144-165
• Aspeborg H, Schrader J, Coutinho PM, Stam M, Kallas Å, Djerbi S, Nilsson P, Denman S, Amini B, Sterky F, Master E, Sandberg G, Mellerowicz E, Sundberg B, Henrissat B, Teeri TT (2005) Carbohydrate-active enzymes involved in the secondary cell wall biogenesis in hybrid aspen. Plant Physiol 137: 983-997
• Geisler-Lee J, Geisler M, Coutinho PM, Segerman B, Nishikubo N, Takahashi J, Aspeborg H, Djerbi S, Master E, Andersson-Gunnerås S, Sundberg B, Karpinski S, Teeri TT, Kleczkowski LA, Henrissat B, Mellerowicz EJ (2006) Poplar carbohydrate-active enzymes. Gene identification and expression analyses. Plant Physiol 140: 946-962
• Schrader J, Nilsson J, Mellerowicz E, Berglund A, Nilsson P, Hertzberg M, Sandberg G (2004) A high-resolution transcript profile across the wood-forming meristem of poplar identifies potential regulators of cambial stem cell identity. Plant Cell 16: 2278-2292
• Zhong R, Pena MJ, Zhou G-K, Nairn CJ, Wood-Jones A, Richardson EA, Morrison III WH, Darvill AG, York WS, Ye Z-H (2005) Arabidopsis Fragile Fiber8, which encodes a putative glucuronyltransferase, is essential for normal secondary wall synthesis. Plant Cell 17: 3390–3408.