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β-Galactosidases and Fasciclin-like Arabinogalactan Proteins in Flax (Linum usitatissimum) Phloem Fibre Development Open Access


Other title
Linum usitatissimum
Fasciclin-like Arabinogalactan Protein
glycosyl hydrolase 35
Type of item
Degree grantor
University of Alberta
Author or creator
Hobson, Neil Robert
Supervisor and department
Deyholos, Michael (Biological Sciences)
Examining committee member and department
Douglas, Carl (Botany, University of British Columbia)
Hall, Jocelyn (Biological Sciences)
Scarpella, Enrico (Biological Sciences)
Hacke, Uwe (Renewable Resources)
Deyholos, Michael (Biological Sciences)
Department of Biological Sciences
Plant Biology
Date accepted
Graduation date
Doctor of Philosophy
Degree level
The phloem fibres of flax (Linum usitatissimum) have specialized, cellulose-rich secondary walls of the gelatinous type (G-type), which give the fibres remarkable strength. G-type walls are also found in tension wood of many trees. β-galactosidases (BGAL) and fasciclin-like arabinogalactan (FLA) genes are expressed during development of G-type walls in flax, but the functions of these genes and their possible interactions are not well understood. The recent assembly of the flax genome, to which I contributed, afforded an opportunity to characterize the BGAL and FLA gene families of flax. Each of these families comprises 43 predicted genes. Comparison of the BGAL family structure between species revealed the expansion and contraction of distinct sub-families, perhaps correlated with specialization of cell wall composition of flax tissues during its evolution and domestication. Phylogenetic analyses of the FLA gene family revealed a sub-family and an amino acid motif unique to the Rosids that is represented by many FLA genes known to be expressed in G-type walls. Transcript expression profiling of the BGAL and FLA families in 12 different flax tissues identified multiple genes from each family that were highly expressed in developing fibres. Transgenic analyses of selected, fibre-enriched genes (LuBGAL1 and LuFLA1) were conducted, first by generating promoter-reporter gene fusions. Within stems, the upstream regions of each of these genes directed reporter gene expression preferentially to developing phloem fibres. Because the RNAi loss-of-funtion phenotype of LuBGAL1 had been previously shown to reduce fibre strength and crystalinity, I extended this functional analysis by producing and characterizing lines overexpressing LuBGAL1 transcripts. I was unable to obtain evidence that LuBGAL1 overexpression affected the composition or mechanical properties of phloem fibres, suggesting that LuBGAL1 may be necessary but not sufficient for G-type wall development. I also characterized transgenic lines bearing an RNAi construct targeted towards LuFLA35 (which is closely related to LuFLA1 and whose transcripts are likewise highly enriched in fibres). LuFLA35-RNAi lines were slightly diminished in tensile strength in flax stems, providing the first evidence that FLAs are functionally required for G-type fibre development in flax.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Hobson N, and Deyholos MK (2013) LuFLA1PRO and LuBGAL1PRO promote gene expression in the phloem fibres of flax (Linum usitatissimum). Plant Cell Reports 32:517-528.Hobson N, and Deyholos MK (2013) Genomic and expression analysis of the flax (Linum usitatissimum) family of glycosyl hydrolase 35 genes. BMC 14: 344.Hobson N, Roach MJ, and Deyholos MK (2010) Gene expression in tension wood and bast fibers. Russian Journal of Plant Physiology 57:321-327.

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