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

• Author / Creator

  Hobson, Neil Robert

• 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.

• Subjects / Keywords

  • Fibre
  • Flax
  • Fasciclin-like Arabinogalactan Protein
  • Glycosyl hydrolase 35
  • Β-Galactosidase
  • Promoter
  • Phloem
  • Linum usitatissimum

• Graduation date

  Fall 2013

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3X05XK5B

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.