Oomycete effector HaRxL106 interacts with Arabidopsis RADICAL INDUCED CELL DEATH1 and suppresses NPR1-dependent immunity
L. WIRTHMUELLER (1), S. Asai (2), G. Rallapalli (3), D. Kim (3), G. Fabro (4), M. Wrzaczek (5), J. Kangasjarvi (6), J. Sklenar (3), F. Menke (3), M. Banfield (7), J. Jones (3) (1) Freie Universität Berlin, Germany; (2) RIKEN Center for Sustainable Resource Science, Japan; (3) The Sainsbury Laboratory, United Kingdom; (4) Research Centre in Biological Chemistry of Córdoba, Argentina; (5) University of Helsinki, Finland; (6) University of Helsinki, Finland; (7) John Innes Centre, United Kingdom

The oomycete pathogen Hyaloperonospora arabidopsidis (Hpa) causes downy mildew on Arabidopsis. We focus on Hpa effector proteins that are targeted to the host cell nucleus aiming to understand how these proteins suppress immunity. Hpa effector HaRxL106 renders plants more susceptible to biotrophic pathogens when expressed as a transgene in Arabidopsis. Transcriptome profiling of HaRxL106-expressing lines revealed that NPR1 target genes are underexpressed compared to wild type. Under short day conditions, non-infected 35S::NPR1-GFP plants show a stunted morphology and constitutively express PR genes. These hallmarks of constitutive defense activation are suppressed by HaRxL106. NPR1-GFP protein accumulation and localization are not affected by HaRxL106, suggesting that the effector may interfere with defense gene expression on chromatin level. Therefore, HaRxL106 likely targets nuclear defense regulators that function downstream of NPR1. The cellular NPR1 pool distributes between disulfide-linked oligomers and the defense activating monomeric form. HaRxL106 interacts with RADICAL INDUCED CELL DEATH1 (RCD1). Knocking out RCD1 results in elevated NO levels and therefore might affect NPR1’s redox status. Consistently, we find that NPR1 target genes are under-expressed in an rcd1 mutant. Therefore, RCD1 is a novel regulator of NPR1. We will present our work addressing how Hpa effector HaRxL106 modifies RCD1 function and how this suppresses plant immunity.

Abstract Number: P9-322
Session Type: Poster