Pseudomonas syringae pv tomato DC3000 is a Gram-negative bacterium that utilizes a type three secretion system to translocate effector proteins into plant cells to promote pathogenesis. There are ~30 effectors secreted by Pst DC3000 and the effectors HopM1 and AvrPto have both been implicated in targeting host vesicle trafficking systems. HopM1 has been shown to promote disease by targeting HopM1 interactor 7 (MIN7). MIN7 contains the SEC7 domain, the catalytic domain of ADP-ribosylation factor (ARF) guanine nucleotide exchange factors (GEFs). ARF GEFs promote the exchange of GTP for GDP on ARF GTPases, but GEF activity has not been demonstrated for MIN7. In this research I show that the SEC7 domain of MIN7 is capable of promoting the exchange of GTP for GDP on an Arabidopsis ARF GTPase. In addition, I found that MIN7::DsRed was partially co-localized with at least five Arabidopsis ARFs. min7 plants are compromised in salicylic acid (SA)-dependent defense and display hypersensitive cell death to benzothiadiazole (BTH), a functional analogue of SA. Two Arabidopsis lines with T-DNA insertions in the ARF-like B1 (ARL-B1) gene are found to be hypersensitive to BTH. Unlike min7 plants, however, the ARL-B1 knockout plants are not compromised in BTH-induced defense. Thus, BTH hypersensitivity and deficient BTH-induced defense can be uncoupled. AvrPto is an effector that compromises plant cell wall-based defense. AvrPto interacts in the yeast two-hybrid system with the RabE1 GTPases, a family of Rab GTPases predicted to be involved in polarized secretion in Arabidopsis. I found that AvrPto interacts with wild type RAB-E1d and RAB-E1d-Q74L (predicted to be GTP bound and active) but not with RAB-E1d-S29N (predicted to be GDP-bound and inactive). To better understand the function of RabE1 in the cell, I used the yeast two-hybrid screen to identify two Arabidopsis interactors of RabE1, REI1 and REI2. REI1 is annotated as a receptor-like kinase, and REI2 contains a SEC14-like domain.
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