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Auto-activated maize R protein recognizes a bacterial effector to trigger incomplete disease resistance in Arabidopsis thaliana

Qi Li: Virginia Tech

<div>Rice bacterial leaf streak (BLS) disease caused by the gram-negative bacterium <em>Xanthomonas oryzae</em> pv. <em>oryzicola</em> (<em>Xoc</em>) is one of the most important rice diseases in Asia and Africa. We previously identified a maize disease resistance gene, <em>Rxo1</em>, which conditions resistance to <em>Xoc</em> strains carrying the type 3 effector AvrRxo1 in transgenic maize and rice plants. However, the mechanism of Rox1/AvrRxo1-mediated disease resistance is still elusive. It is also unclear if Rxo1 can be functional transferred to other plant species. To this end, we generated transgenic Arabidopsis plants expressing <em>Rxo1</em>. However, the Arabidopsis-Rxo1 plants failed to confer disease resistance to <em>Pseudomonas syringae </em>pv. <em>tomato (Pst) </em>DC3000 expressing the <em>Xoc-avrRxo1 </em>gene. To understand why <em>Rxo1</em> is not functional in <em>Arabidopsis,</em> and test the possibility of modifying <em>Rxo1</em> to reconstitute its functionality in Arabidopsis, we generated an <em>Rxo1</em> autoactivation mutant D508V. We demonstrated that Rxo1-D508V triggers cell death in <em>N. benthamiana </em>and <em>Arabidopsis</em> plants. Interestingly, transgenic Arabidopsis plants expressing <em>Rxo1-D508V</em> can specifically recognize <em>Xoc-avrRxo1, </em>and trigger incomplete disease resistance to <em>Pst </em>DC3000 carrying <em>Xoc-avrRxo1</em>. We further demonstrated that Xoc-avrRxo1 directly interacts with the NBS domain alone but not the full length of Rxo1 <em>in vitro </em>and <em>in vivo</em>. We hypothesize that Rxo1-D508V may have altered protein structure allowing it to expose the NBS domain and interact with AvrRxo1 in Arabidopsis plant cells. The direct interaction may partially explain the functionality of Rox1-D508V/AvrRxo1 in <em>Arabidopsis</em>.</div>