<p>Systemic Acquired Resistance (SAR) is a plant defense response induced by an initial infection in one part of the plant that leads to broad-spectrum resistance to normally virulent pathogens in distant naïve leaves. As part of the Cameron research team, I contributed to demonstrating that the lipid transfer protein, DIR1 is required for SAR long distance signaling in <em>Arabidopsis</em> and travels from induced to distant tissues during SAR. A highly similar<em> Arabidopsis</em> protein DIR1-like was identified and is thought to be responsible for the occasional SAR-competent phenotype observed in the <em>dir1-1</em> mutant. This work provides evidence for the idea that DIR1 and DIR1-like are paralogs created by a recent duplication event and that similar to DIR1, DIR1-like may travel to distant tissues during SAR. To better understand DIR1 and DIR1-like contribution during SAR, <em>dir1-1dir1-like</em> double mutant transgenic plants were created as well as transgenic plants expressing epitope- (HA and FLAG) and fluorescent- (iLOV and phiLOV) tagged DIR1 and DIR1-like to facilitate visualization of movement during SAR. Several putative DIR1 orthologs were identified in crop plants and cucumber CucDIR1 was shown to be functionally equivalent to AtDIR1 in <em>dir1-1</em> complementation studies providing further evidence that DIR1 plays an important role in SAR across plant species. By analyzing conservation between DIR1, DIR1-like and the putative DIR1 orthologs, several protein residues were identified that may be important for DIR1 function during SAR. DIR1 proteins were modified at these sites and the importance of these residues was supported by the reduced binding of the TNS hydrophobic probe in these DIR1 variants. Taken together, this thesis suggests that DIR1 and DIR1-like both participate in SAR in <em>Arabidopsis</em>, that DIR1 crop orthologs are also important for the SAR response and that DIR1 possesses several sites that are critical for its function in long distance SAR signaling.</p> / Doctor of Philosophy (PhD)