Oomycete Effector HARXL106 Interacts With Arabidopsis Radica Induced Cell Death and Suppresses NPR1-dependent and - independent immune pathways

LENNART WIRTHMUELLER; SHUTA ASAI; GANASHYAM RALLAPALLI; GEORGINA FABRO; WRZACZEK M; KANGASJARVI J; MARK BANFIELD; JONATHAN D G JONES

Rodas

Congreso; IS-MPMI Congress Rhodes 2014; 2014

International Society of Molecular Plant Microbe Interactions

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 and we are aiming to understand how these effectors suppress immunity. Hpa effector HaRxL106 renders plants more susceptible to biotrophic pathogens when expressed as a transgene in Arabidopsis. Transcriptome profiling of transgenic lines expressing HaRxL106 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 co-expression of HaRxL106. NPR1-GFP protein accumulation and localization are not affected by HaRxL106, suggesting that the effector may interfere with PR gene expression at the chromatin level. HaRxL106 expression also reverts NPR1-independent constitutive defense gene expression and stunted growth in the snc1 mutant. Therefore, HaRxL106 likely targets nuclear defense regulators that function downstream of snc1 and NPR1. HaRxL106 interacts with Arabidopsis RADICAL INDUCED CELL DEATH1 (RCD1) and a mutant variant of HaRxL106 that does not bind RCD1 fails to suppress immunity. The cellular NPR1 pool distributes between disulfide-linked oligomers and the defense activating monomeric forma. Knocking out RCD1 results in elevated NO levels and therefore might affect NPR1 redox status. Consistently, we find that NPR1 target genes are underexpressed in an rcd1 mutant. Therefore, RCD1 is a novel regulator of NPR1 activity. We will present our work addressing how Hpa effector HaRxL106 modifies RCD1 function and how this suppresses plant immunity.