RT Journal Article SR Electronic T1 An oomycete effector protein induces shade avoidance in Arabidopsis and attenuates salicylate signaling by binding to host proteins of the RADICAL-INDUCED CELL DEATH1 family JF bioRxiv FD Cold Spring Harbor Laboratory SP 137844 DO 10.1101/137844 A1 Lennart Wirthmueller A1 Shuta Asai A1 Ghanasyam Rallapalli A1 Jan Sklenar A1 Georgina Fabro A1 Dae Sung Kim A1 Ruth Lintermann A1 Pinja Jaspers A1 Michael Wrzaczek A1 Jaakko Kangasjärvi A1 Daniel MacLean A1 Frank L. H. Menke A1 Mark J. Banfield A1 Jonathan D. G. Jones YR 2017 UL http://biorxiv.org/content/early/2017/05/14/137844.abstract AB The oomycete pathogen Hyaloperonospora arabidopsidis (Hpa) causes downy mildew disease on Arabidopsis. During infection, Hpa like other biotrophic pathogens, suppresses activation of plant innate immunity by translocating effector proteins into host cells. Some of these effectors localize to the host cell nucleus where they may manipulate transcriptional reprogramming of plant defense genes. Here we report that the nuclear-localized Hpa effector HaRxL106, when expressed in Arabidopsis, induces shade avoidance and attenuates the transcriptional response to the defense signaling molecule salicylic acid. HaRxL106 interacts with RADICAL-INDUCED CELL DEATH1 (RCD1) and loss of RCD1 function renders Arabidopsis resilient against HaRxL106-mediated suppression of immunity. To further characterize the molecular functions of RCD1 we solved a crystal structure of RCD1’s Poly-(ADP-ribose)-Polymerase (PARP) domain and, based on non-conservation of amino acids constituting the active site of canonical PARPs, conclude that RCD1 has no PARP activity. We report that RCD1-type proteins are phosphorylated and identified histone-modifying Mut9-like kinases (MLKs) as RCD1-interacting proteins. A mlk1,3,4 triple mutant exhibits stronger SA-induced defense marker gene expression compared to wild-type plants. Our data suggest that HaRxL106 suppresses Arabidopsis innate immunity by manipulating the function(s) of RCD1 in the host cell nucleus and point towards a role of RCD1 as a transcriptional co-regulator that integrates signals from light and pathogen sensors.