Systemic acquired resistance (SAR) is a defense response induced by an initial
localized infection that leads to the generation of long-distance immune signals that
travel to distant leaves to provide enhanced resistance to subsequent infections. The
lipid transfer protein (LTP) DEFECTIVE IN INDUCED RESISTANCE1 (DIR1) travels
via the phloem from induced to distant leaves during SAR and may chaperone
several long-distance signal candidates. In this thesis, the role of DIR1 during SAR is
explored by examining the route of DIR1 movement, investigating the conservation
of DIR1 structure and function, and by identifying DIR1-interacting proteins. I
demonstrate that Arabidopsis plant lines with restricted cell-to-cell movement through
plasmodesmata are negatively impacted in long-distance DIR1 movement,
suggesting that cell-to-cell movement is important for DIR1 to access distant leaves.
To elucidate the molecular function of DIR1, orthology analysis was performed with
putative DIR1 orthologs. Structurally important amino acid residues that contribute to
the hydrophobicity of the LTP cavity were identified, supporting the idea that DIR1
binds a hydrophobic ligand during SAR. RNAi-mediated knockdown of the DIR1
paralog DIR1-like did not impact the SAR response, supporting the idea that DIR1-
like plays a lesser role in SAR. In addition, targeted protein-protein interaction assays
determined that LTP1 and LTP2 interact with DIR1, and SAR phenotypic analysis of
an ltp2-1 mutant supported a role for LTP2 in SAR. Lastly, a comparative proteomics
approach identified several proteins with differential abundance in phloem exudates
collected during the induction of SAR. Of these proteins, m-type thioredoxins, a
major latex protein-like protein, and the UV-B photoreceptor UVR8 were essential for
the manifestation of SAR. Together, these data provide insight into DIR1 function by
identifying the importance of cell-to-cell movement through plasmodesmata, the
DIR1 hydrophobic cavity, and DIR1-interacting proteins for DIR1-mediated SAR. In
addition, this work identifies new phloem-localized proteins that contribute to the
SAR response, providing fundamental knowledge on protein composition within the
phloem during biotic stress. / Dissertation / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/20029 |
| Date | January 2016 |
| Creators | Carella, Philip |
| Contributors | Cameron, Robin K., Weretilnyk, Elizabeth A., Daniel, Juliet, Biology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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