Abstract
Pb1 (Panicle Blast1) is a panicle blast resistance gene derived from indica rice "Modan". The Pb1 resistance is durable and of broad spectrum for fungal races. We previously reported that Pb1 encodes a CC-NB-LRR-type R protein and the protein interacts with WRKY45, which plays a role in induced resistance via the salicylic pathway. To test the WRKY45 dependence of Pb1-mediated blast resistance, we knocked down WRKY45 in a Pb1 cultivar (Pb1-line/WRKY45-kd) and Pb1-ox Nipponbare (Pb1-ox/WRKY45-kd). In both the cases, Pb1-mediated blast resistance was largely compromised by WRKY45 knockdown, suggesting that Pb1 resistance is dependent on WRKY45. Addition of nuclear export sequence to Pb1 largely abolished the resistance upon its overexpression, indicating that nuclear localization is necessary for Pb1 function. Recently, WRKY45 was found to be regulated by ubiquitin proteasome system (UPS). We found that Pb1 protected WRKY45 from UPS via specific protein-protein interaction. Blast infection induced higher levels of WRKY45 accumulation in Pb1-ox rice than in control rice. These results suggest that Pb1 resistance is mediated by protection of WRKY45 from its proteasome degradation.
