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Doctoral thesis, 2012

Synthesis of glucuronoxylan in higher and lower plants

Hörnblad, Emma


The hemicellulose glucuronoxylan (GX) is the second most abundant polysaccharide after cellulose in the secondary cell walls of angiosperms and contributes significantly to the properties of wood as raw materials. Despite this, very little is known about the biosynthesis of hemicellulose. The thesis is based on studies performed in Physcomitrella patens, Arabidopsis thaliana, and Populus plants with the aim to increase the understanding of glucuronoxylan synthesis, and with main focus on the role of the IRX10 gene family. A number of genes have proven to be involved in GX biosynthesis in Arabidopsis, namely IRREGULAR XYLEM (IRX) 9, IRX14, IRX8, FRAGILE FIBER (FRA) 8 and PARVUS. This thesis presents two new genes, IRX10 and its close homolog IRX10- LIKE (L), which can now be added to the group of presumed GX biosynthesis genes. In addition, identification and characterisation of three homologs (IRX9-L, IRX14-L and F8H) of previously identified GX synthesis genes is described. Complementation experiments and morphological studies confirmed redundancy between the IRX9 and IRX9-L, IRX14 and IRX14-L, and the FRA8 and F8H pairs of genes in Arabidopsis. A bioinformatics based approach has led to the identification of four putative homologs in Populus trichocarpa (PtGT47A-1, PtGT47A-2, PtGT47D-1, and PtGT47D-4) of AtIRX10, and one putative homolog from Physcomitrella (PpGT47D). Experiments further confirmed functional conservation between the Arabidopsis (IRX10) and Populus GT47A proteins, and partial functional conservation between the Populus GT47D, the Physcomitrella GT47D and Arabidopsis IRX10 proteins. The work supports the existence of an Arabidopsis GX backbone biosynthesis complex in which AtIRX10 and AtIRX10-L form an essential component together with AtIRX9 and AtIRX14. It also suggests that parts of the GX biosynthesis machinery are conserved across embryophytes. Finally, work presented in this thesis indicates that the IRX10 gene family has gone through a subfunctionalisation event during the evolution.


Glucuronoxylan; Wood formation; Secondary cell wall; Arabidopsis; Populus; Physcomitrella

Published in

Acta Universitatis Agriculturae Sueciae
2012, number: 2012:8
ISBN: 978-91-576-7692-4
Publisher: Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences

Authors' information

Hörnblad, Emma
Swedish University of Agricultural Sciences, Department of Forest Genetics and Plant Physiology

UKÄ Subject classification

Genetics and Breeding
Plant Biotechnology

URI (permanent link to this page)