A pathogenic long non-coding RNA redesigns the epigenetic landscape of the infected cells by subverting host Histone Deacetylase 6 activity

[EN] Viroids - ancient plant-pathogenic long noncoding RNAs - have developed a singular evolutionary strategy based on reprogramming specific phases of host-metabolism to ensure that their infection cycle can be completed in infected cells. However, the molecular aspects governing this transregulatory phenomenon remain elusive. Here, we use immunoprecipitation assays and bisulfite sequencing of rDNA to shown that, in infected cucumber and Nicotiana benthamina plants, Hop stunt viroid (HSVd) recruits and functionally subverts Histone Deacetylase 6 (HDA6) to promote host-epigenetic alterations that trigger the transcriptional alterations observed during viroid pathogenesis. This notion is supported by the demonstration that, during infection, the HSVd-HDA6 complex occurs invivo and that endogenous HDA6 expression is increased in HSVd-infected cells. Moreover, transient overexpression of recombinant HDA6 reverts the hypomethylation status of rDNA observed in HSVd-infected plants and reduces viroid accumulation. We hypothesize that the host-transcriptional alterations induced as a consequence of viroid-mediated HDA6 recruitment favor spurious recognition of HSVd-RNA as an RNA Pol II template, thereby improving viroid replication. Our results constitute the first description of a physical and functional interaction between a pathogenic RNA and a component of the host RNA silencing mechanism, providing novel evidence of the potential of these pathogenic lncRNAs to physically redesign the host-cell environment and reprogram their regulatory mechanisms.The authors thank Dr M. Fares for the contribution to the statistical analysis of the data and Dr G. Martinez for the critical reading of this manuscript. This work was supported by grants AGL2013-47886-R and BIO2014-61826-EXP (GG) and BIO2014-54862-R (VP) from the Spanish Granting Agency (Direccion General Investigacion Cientifica).Castellano Perez, M.; Pallás Benet, V.; Gomez, GG. (2016). A pathogenic long non-coding RNA redesigns the epigenetic landscape of the infected cells by subverting host Histone Deacetylase 6 activity. New Phytologist. 211(4):1311-1322. doi:10.1111/nph.14001S13111322211

Protein-protein interactions in the RPS4/RRS1 immune receptor complex

Plant NLR (Nucleotide-binding domain and Leucine-rich Repeat) immune receptor proteins are encoded by Resistance (R) genes and confer specific resistance to pathogen races that carry the corresponding recognized effectors. Some NLR proteins function in pairs, forming receptor complexes for the perception of specific effectors. We show here that the Arabidopsis RPS4 and RRS1 NLR proteins are both required to make an authentic immune complex. Over-expression of RPS4 in tobacco or in Arabidopsis results in constitutive defense activation; this phenotype is suppressed in the presence of RRS1. RRS1 protein co-immunoprecipitates (co-IPs) with itself in the presence or absence of RPS4, but in contrast, RPS4 does not associate with itself in the absence of RRS1. In the presence of RRS1, RPS4 associates with defense signaling regulator EDS1 solely in the nucleus, in contrast to the extra-nuclear location found in the absence of RRS1. The AvrRps4 effector does not disrupt RPS4-EDS1 association in the presence of RRS1. In the absence of RRS1, AvrRps4 interacts with EDS1, forming nucleocytoplasmic aggregates, the formation of which is disturbed by the co-expression of PAD4 but not by SAG101. These data indicate that the study of an immune receptor protein complex in the absence of all components can result in misleading inferences, and reveals an NLR complex that dynamically interacts with the immune regulators EDS1/PAD4 or EDS1/SAG101, and with effectors, during the process by which effector recognition is converted to defense activation

Chloroplast Stromules Function during Innate Immunity

Inter-organellar communication is vital for successful innate immune responses that confer defense against pathogens. However, little is known about how chloroplasts, which are a major production site of pro-defense molecules, communicate and coordinate with other organelles during defense. Here we show that chloroplasts send out dynamic tubular extensions called stromules during innate immunity or exogenous application of the pro-defense signals, hydrogen peroxide (H(2)O(2)) and salicylic acid (SA). Interestingly, numerous stromules surround nuclei during defense response and these connections correlate with an accumulation of chloroplast-localized NRIP1 defense protein and H(2)O(2) in the nucleus. Furthermore, silencing and knockout of CHloroplast Unusual Positioning 1 (CHUP1) that encodes a chloroplast outer envelope protein constitutively induces stromules in the absence of pathogen infection and enhances programmed cell death (PCD). These results support a model in which stromules aid in the amplification and/or transport of pro-defense signals into the nucleus and other subcellular compartments during immunity