Pectin remodelling enzymes of flax and their roles in fiber development

• Author / Creator

  Pinzon Latorre, David

• Linum usitatissimum (flax) is an annual eudicot for which two types are cultivated: linseed and fiber flax. The stem fibers of linseed are not generally used commercially because they are of lower quality and yield than those obtained from fiber flax. Moreover, the extraction of fibers by dew-retting is not possible in the climate of Canada. Our goal was to study the pectin composition in the cell wall of the fibers and surrounding cells and find a set of candidate pectin-modifying genes with roles in fiber development. Flax phloem fibers elongate intrusively by diffuse growth, so, they need to penetrate between adjacent cells during elongation through the middle lamella. This is hypothesized to require dissolution of the middle lamella and sufficient rigidity of the fiber to allow penetration, while maintaining flexibility for cell wall expansion. The degree and pattern of methylesterification of galacturonic acid (GalA) residues in homogalacturonan (HG) influences the rigidity of the middle lamella and cell wall. Pectin methylesterases (PME) mediate the demethylesterification of GalA in muro, in either a block-wise fashion (resulting in rigidification), or random fashion (resulting in wall loosening via the subsequent action of polygalacturonases (PG) or pectate lyase like proteins (PLL). Through immunohistochemistry, I defined some of the modifications that occur in pectin during fiber elongation, and generated a model of fiber development, in which low methylesterification of elongating fibers is associated with abundant galactan side chains that help to regulate interactions between pectins and prevent premature rigidification of fiber cell wall during its growth. I characterized the PME, PMEI and PLL gene families in flax using the recently sequenced genome, and using transcript profiling assays on nine different stages of development I defined a set of candidate genes with roles in fiber development. I expressed one of these PMEIs in E. coli and demonstrated that it was able to inhibit most of the native PME activity in the upper portion of the flax stem. Together, these results clarify the role of pectin modification during bast fiber development and identify targets for crop improvement.

• Subjects / Keywords

  • Cell wall
  • Galactan
  • Homogalacturonan
  • Flax fiber
  • Pectinesterase
  • Pectin methylesterase

• Graduation date

  Fall 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3VT18

• 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.