Biology subjects

Wirthmueller, L.

Publications and source records attributed to Wirthmueller, L..

9 recordsLinked to original sources

bioRxiv2026

Decoy diversification underpins the regulation of an NLR-mediated autoimmunity

Appropriate activation of innate immune receptors is vital for the plant immune system. Immune activation must be strong and robust upon invasion by rapidly evolving pathogen species, while staying inactive in the absence of a pathogen to avoid constitutive defense responses that inhibit plant growth. Nucleotide-binding leucine-rich repeat receptors (NLRs) are intracellular proteins that surveil for pathogen invasion, often by direct or indirect perception of pathogen effector proteins. Indirect recognition of pathogen effector proteins, through monitoring the integrity of guardee or decoy proteins, can allow for a single NLR to detect a wide range of pathogen effectors. In this work, we investigated how the Solanaceae NLR NbPtr1 can recognize six different effector proteins from the bacterial pathogens Pseudomonas syringae, Xanthomonas perforans, and Ralstonia pseudosolanacearum. We identified several NOI-domain containing proteins that are guarded by NbPtr1. These NOI proteins share homology with, but are distinct from, RPM1 INTERACTING PROTEIN 4 (RIN4), a well-known guardee in Arabidopsis. Virus-induced gene silencing and CRISPR/Cas9-assisted deletion of NbNOI genes resulted in stunted growth dependent on NbPtr1 activity. Negative regulation of NbPtr1 requires the interaction between NbPtr1 and the suppressor NbNOIs. A conserved threonine residue of the NOI proteins is required for this interaction and fits into a putative binding pocket of NbPtr1 based on protein modeling. This threonine residue is modified by some of the recognized effector proteins. Our study uncovers the regulatory mechanism of an autoactive NLR and highlights the importance of decoy diversification in establishing compatibility with NLRs.

plant biology↗

bioRxiv2025

An oomycete effector that induces shade avoidance like growth and suppresses plant defenses targets the AUX/IAA protein IAA11

Filamentous pathogens, such as oomycetes, employ multiple strategies to suppress plant immunity, one of which involves manipulating phytohormone signaling pathways. The effector HaRxL106 from Hyaloperonospora arabidopsidis (Hpa), known to induce shade avoidance syndrome (SAS)-like growth, has previously been shown to interact with brassinosteroid signaling components. Here, we investigate the role of HaRxL106 in altering auxin signaling, revealing that HaRxL106 targets the AUX/IAA protein IAA11, a key negative regulator of auxin responses. Our data suggest that HaRxL106 impedes the repressive function of IAA11, enhancing auxin signaling and promoting SAS, which concurrently suppresses plant immune responses. These findings provide insights into how pathogen effectors manipulate plant growth and immunity to facilitate infection.

plant biology↗

bioRxiv2024

Downy mildew effector HaRxL106 interacts with the transcription factor BIM1 altering plant growth, BR signaling and susceptibility to pathogens

Hyaloperonospora arabidopsidis (Hpa) is an oomycete pathogen that causes downy mildew disease on Arabidopsis. This obligate biotroph manipulates the homeostasis of its host plant by secreting numerous effector proteins, among which are the RxLR-effectors. Identifying the host targets of effectors and understanding how their manipulation facilitates colonization of plants is key to improve plant resistance to pathogens. Here we characterize the interaction between the RxLR effector HaRxL106 and BIM1, an Arabidopsis transcription factor (TF) involved in Brassinosteroid (BR) signaling. We report that HaRxL106 interacts with BIM1 in vitro and in planta. BIM1 is required by the effector to increase the host plant susceptibility to (hemi)biotrophic pathogens, and thus can be regarded as a susceptibility factor. Mechanistically, HaRxL106 requires BIM1 to induce the transcriptional activation of BR-responsive genes and cause alterations in plant growth patterns that phenocopy the shade avoidance syndrome. Our results support previous observations of antagonistic interactions between activation of BR signaling and suppression of plant immune responses and reveal that BIM1, a new player in this crosstalk, is manipulated by the pathogenic effector HaRxL106. SIGNIFICANCE STATEMENTOur study reveals that the Arabidopsis transcription factor BIM1 plays a key role as a susceptibility factor that is manipulated by the oomycete effector HaRxL106 to induce the Brassinosteroid (BR) signaling pathway and suppress plant immunity. HaRxL106 induces BIM1-dependent expression of BR-responsive genes which affects normal plant growth generating a shade avoidance-like syndrome that impacts negatively on plant defenses against bacterial and oomycete pathogens.

plant biology↗

bioRxiv2023

Untargeted proteomics identifies plant substrates of the bacterial-derived ADP-ribosyltransferase AvrRpm1

One class of enzymes that plant pathogens employ to manipulate innate immunity and physiology of the infected cells are host-targeted ADP-ribosyltransferases. The bacterial pathogen Pseudomonas syringae uses its type III secretion system to inject several effector proteins with ADP-ribosyltransferase activity into plant cells. One of them, AvrRpm1, ADP-ribosylates the plasma membrane-associated RPM1-INTERACTING PROTEIN 4 (RIN4) in Glycine max and Arabidopsis thaliana to attenuate targeted secretion of defense-promoting compounds. Substrate identification of host-targeted ADP-ribosyltransferases is complicated by the biochemical lability of the protein modification during plant protein extraction and in several cases required prior knowledge on plant immune signaling pathways that are impaired by the ADP-ribosylating type III effector. Using the AvrRpm1-RIN4 pair as a proof-of-concept, we present an untargeted proteomics workflow for enrichment and detection of ADP-ribosylated proteins and peptides from plant cell extracts that in several cases provides site-resolution for the modification.

plant biology↗

bioRxiv2021

The superior salinity tolerance of wheat cultivar Shanrong No. 3 cannot be attributed to elevated Ta-sro1 poly(ADP-ribose) polymerase activity

Saline soils limit the production of important staple crops such as wheat, particularly in arid and semiarid regions. Salt tolerance is a multi-gene trait and this complicates breeding of wheat varieties that deliver high yields under saline soil conditions. Notably, the elevated salinity tolerance of wheat cultivar Shanrong No. 3 (SR3) has been linked to a specific proteoform of the wheat SIMILAR TO RCD1 ONE (SRO1) protein that was created in an asymmetric genome hybridization with tall wheat grass. The two amino acid polymorphisms of the Ta-sro1 proteoform enhance the poly(ADP-ribose) polymerase (PARP) activity of the protein suggesting that altered poly-ADP-ribosylation of unknown substrate proteins or nucleic acids underlie the elevated salinity tolerance of cultivar SR3. To elucidate the molecular basis for the elevated PARP activity of the Ta-sro1 proteoform we solved a crystal structure of the catalytic PARP domain. Surprisingly, the structure revealed that the postulated binding site for the co-substrate NAD+ substantially differs from the structurally conserved NAD+ binding sites of canonical PARP enzymes. Consistently, we find that Ta-sro1 does not bind NAD+ and lacks ADP-ribosyltransferase activity. Therefore, although the structure revealed that one of the polymorphic amino acids is located close to the proposed active site, the elevated salinity tolerance of cultivar SR3 cannot be explained by altered ADP-ribosyltransferase activity of Ta-sro1.

plant biology↗

bioRxiv2020

Arabidopsis Poly(ADP-ribose)-binding protein RCD1 interacts with Photoregulatory Protein Kinases in nuclear bodies

Continuous reprogramming of gene expression in response to environmental signals is required for plant survival in changing environment. One mechanism responsible for this is signaling through hub proteins that integrate external stimuli and transcriptional responses. RADICAL-INDUCED CELL DEATH1 (RCD1) functions as a nuclear hub protein, that interacts with a variety of transcription factors through its C-terminal RST domain and acts as a co-regulator of numerous stress responses in plants. Here, a previously unknown function for RCD1 as a novel plant poly(ADP-ribose) (PAR) reader protein is described. RCD1 localizes to specific locations inside the nucleus, in a PAR-dependent manner; its N-terminal WWE domain o binds PAR and together with the PARP-like domain determines its localization to nuclear bodies (NBs), which is prevented by inhibition of PAR synthesis. RCD1 also interacts with Photoregulatory Protein Kinases (PPKs) that co-localize with RCD1 in the NBs. The PPKs, that have been associated with circadian clock, abscisic acid, and light signaling pathways, phosphorylate RCD1 at multiple sites in the intrinsically disordered region between the WWE and PARP-like domains. This affects its stability and functions in the nucleus and1 provides a mechanism where the turnover of a PAR-binding transcriptional co-regulator is controlled by nuclear protein kinases.

plant biology↗

bioRxiv2020

Functional requirement of the Arabidopsis importin-α nuclear transport receptor family in autoimmunity mediated by the NLR protein SNC1

IMPORTIN-3/MOS6 (MODIFIER OF SNC1, 6) is one of nine importin- isoforms in Arabidopsis that recruit nuclear localization signal (NLS)-containing cargo proteins to the nuclear import machinery. IMP-3/MOS6 is required genetically for full autoimmunity of the nucleotide-binding leucine-rich repeat (NLR) immune receptor mutant snc1 (suppressor of npr1-1, constitutive 1) and MOS6 also contributes to basal disease resistance. Here, we investigated the contribution of the other importin- genes to both types of immune responses, and we analyzed potential interactions of all importin- isoforms with SNC1. By using reverse-genetic analyses in Arabidopsis and protein-protein interaction assays in N. benthamiana we provide evidence that among the nine -importins in Arabidopsis, IMP-3/MOS6 is the main nuclear transport receptor of SNC1, and that IMP-3/MOS6 is required selectively for autoimmunity of snc1 and basal resistance to mildly virulent Pseudomonas syringae in Arabidopsis. SIGNIFICANCE STATEMENTSpecific requirement for the Arabidopsis -importin MOS6 in snc1-mediated autoimmunity is explained by selective formation of MOS6-SNC1 nuclear import complexes.

plant biology↗

bioRxiv2018

Nuclear import of Arabidopsis POLY(ADP-RIBOSE) POLYMERASE 2 is mediated by importin-α and a nuclear localization sequence located between the predicted SAP domains

Proteins of the poly(ADP-ribose) polymerase (PARP) family modify target proteins by covalent attachment of ADP-ribose moieties onto amino acid side chains. In Arabidopsis, PARP proteins contribute to repair of DNA lesions and modulate plant responses to various abiotic and biotic stressors. Arabidopsis PARP1 and PARP2 are nuclear proteins and given that their molecular weights exceed the diffusion limit of nuclear pore complexes, an active import mechanism into the nucleus is likely. Here we use confocal microscopy of fluorescent protein-tagged Arabidopsis PARP2 and PARP2 deletion constructs in combination with site-directed mutagenesis to identify a nuclear localization sequence in PARP2 that is required for nuclear import. We report that in co-immunoprecipitation assays PARP2 interacts with several isoforms of the importin- group of nuclear transport adapters and that PARP2 binding to IMPORTIN-2 is mediated by the identified nuclear localization sequence. Our results demonstrate that PARP2 is a cargo protein of the canonical importin-/{beta} nuclear import pathway.

plant biology↗

bioRxiv2017

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

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 RCD1s 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.

plant biology↗