All plant cells are surrounded by one or more cell wall layers. The cell wall serves as a stiff
mechanical support while it allows cells to expand and provide a protective barrier to
invading pathogens. Cell walls are dynamic structures composed of entangled cell wall
polysaccharides that must adopt defined 3D organization to allow their
composition/interactions to be tweaked upon developmental need. Failure to build
functional cell wall architecture will affect plant growth and resistance to stresses. In this
PhD dissertation I explored the role of pectin acetylation in controlling these processes.
Prior to the start of the PhD we had knowledge that manipulating cell wall acetylation
affected the resistance towards pathogens although the underlying mechanism was
unknown. In Manuscript I we investigated a cell wall acetylation mutant called reduced
wall acetylation 2 (rwa2), which displayed reduction in pectin and hemicellulose
acetylation. We found that the increased resistance to pathogens in this mutant was due to
the constitutive upregulation of defenses responses and the concomitant loss of integrity in
the cell wall. Based on the results obtained in Manuscript I, we hypothesized that the loss of
structural integrity in the cell wall was the underlying cause for triggering defenses
response. This hypothesis was tested in Manuscript II. Through a suppressor screen of
30.000 Arabidopsis rwa2 plants and mapping of mutations by next generation sequencing,
we pinpointed pectin deacetylation to be the molecular basis of the structural defects in the
cell wall in rwa2 which in turn were leading to increased resistance to pathogen. Detailed
analysis of polymer dynamics and interactions by multidimensional solid-state NMR
techniques revealed that pectin deacetylation exerts significant impacts on the cell wall
organization, namely polysaccharides-to-polysaccharides interactions. These results suggest
that cell wall acetylation is a mechanism that plants evolved to control cell wall
organization. In Manuscript III, we report the characterization of Arabidopsis mutants
trichome birefringence like (tbl) 10-1 and 10-2, which exhibited specific reduction in
the acetylation in pectins but not hemicelluloses, leading to the suggestion that TBL10
encodes a putative pectin acetyltransferase.
Altogether these data describe the role of pectin acetylation in influencing the molecular
interactions within cell wall components and the environment.