DIR1 Movement During Long Distance Signaling in Systemic Acquired Resistance & Development of a Florescence Based Screen for Age-Related Resistance Mutants

Abstract

<p>Systemic Acquired Resistancc (SAR) is an induced resistance mechanism in which certain localized pathogen infections lead to broad resistance against future attacks in distant tissues. Resistance is transmitted from induced tissues by long distance signals that are perceived in systemic tissue eliciting defence to normally virulent pathogens. Previous research in the Cameron laboratory indicates that DIR1 may function as a long distance signal during SAR. <em>Agrobacterium</em> transient transformation was used to study DIR1 movement in the <em>dir1-1</em> SAR-defective mutant. Lower leaves of <em>dir1-1</em> were infiltrated with <em>Agrobacterium</em> expressing 35S:DIR1-EYFP, followed by inoculation with SAR-inducing <em>Pseudomonas syringae</em> pv. <em>tomato</em> (Pst avrRpt2). Distant leaves were challenged with virulent <em>Pseudomonas syringae pv. tomato</em> (Pst) and bacterial levels were determined. The SAR defect was rescued in <em>dir1-1</em> plants expressing 35S:DIR1EYFP only if SAR was induced. Petiole exudates were collected from these induced leaves and DIR1 was present, suggesting that DIR1 is capable of movement during SAR. Additionally, when cucumber exudates induced for SAR were infiltrated into <em>dir1-1</em> rabidopsis, <em>dir1-1</em> became SAR-competent. Cucumber exudates contained a DIR1-like protein. Taken together, these data suggest that a DIR1-like protein exists in cucumber and functions like DIR1 in Arabidopsis during SAR.</p> <p>Age-Related Resistance (ARR) has been observed in numerous plant species, often resulting in increased disease resistance as plants mature. A genetic screen to identity potential ARR mutants has been developed. The screen used a florescence strain of <em>Pst</em> (<em>Pst</em>-GFPuv) to quantify bacterial levels in infected leaves. A number of parameters were investigated to improve the screen.</p>