Biology subjects

Ahn, H.-K.

Publications and source records attributed to Ahn, H.-K..

8 recordsLinked to original sources

bioRxiv2026

Broad-spectrum polerovirus resistance conferred by a potato TIR-NLR immune receptor

Potato leafroll virus (PLRV) is an economically important viral disease of potato (S. tuberosum). Genetic resistance to this phloem-limited virus is rare, and no cloned resistance (R) genes have been reported. Rladg confers resistance to PLRV in an Andean potato landrace, LOP-868 (Velasquez et al. 2007). We identified the functional Rladg gene as a homolog of the tomato TIR-NLR-encoding Bs4. Rladg interacts with the serine protease domain of the PLRV protein P1, which is essential for virus replication. This recognition is independent of the proteases enzymatic activity, and the Rladg immune receptor oligomerizes upon direct association with the protease. Like PLRV, many poleroviruses contain a serine protease. Despite their diverse amino acid sequences, these proteases are predicted to share similar structures. Rladg recognizes all ten tested polerovirus proteases, suggesting a conserved structural recognition mechanism. We propose that Rladgs broad recognition capacity could enable resistance to poleroviruses in many crop species. Rladg is the first R-gene reported to confer resistance to a phloem-limited pathogen and could provide enhanced resistance to many economically important poleroviruses.

plant biology↗

bioRxiv2025

Structural basis for heat tolerance in plant NLR immune receptors.

Nucleotide-binding leucine-rich repeat (NLR) immune receptors sense pathogen molecules and oligomerize, initiating defense signaling. Some NLRs function poorly at elevated temperatures for unknown reasons. We show that temperature-sensitive NLRs retain ligand binding at elevated temperatures but are impaired in oligomerization. We identify key residues involved in temperature resilience. Structural modeling reveals stabilizing intramolecular interactions of the NB-ARC domain with surface residues of the adjacent leucine-rich repeat (LRR) that preserve receptor integrity and functionality under heat stress. These insights enable in silico classification of NLRs as temperature-sensitive or -tolerant and underpin design of temperature tolerant variants of temperature sensitive NLRs. These findings provide a mechanistic basis for temperature sensitivity in plant immune receptors and enable engineering of temperature-tolerant disease resistance in crops.

plant biology↗

bioRxiv2025

Recognition-dependent activation of the RRS1-R/RPS4 immune receptor complex

The Arabidopsis TIR-NLR immune receptors RPS4 and RRS1 function together to enable recognition of multiple effector proteins including AvrRps4 and PopP2. We show here that both in the presence and absence of effector, RPS4 and RRS1 form an oligomer that does not change in size upon effector provision. Oligomer formation involves interactions between the RPS4 and RRS1 TIR domains and requires nucleotide binding capacity in RPS4. RPS4 mutants that lose TIR domain NADase activity abrogate immune activation but retain oligomerization. A cysteine residue in the RPS4 LRR domain contributes to oligomer stabilization. We propose that upon effector recognition, conformational changes in the complex relieve inhibition of RPS4 TIR domains by RRS1 TIR domains, enabling proximity between RPS4 TIR domains to create NADase activity.

plant biology↗

bioRxiv2022

Oligomerisation of a plant helper NLR requires cell-surface and intracellular immune receptor activation

Plant disease resistance involves both detection of microbial molecular patterns by cell-surface pattern recognition receptors and detection of pathogen effectors by intracellular NLR immune receptors. NLRs are classified as sensor NLRs, involved in effector detection, or helper NLRs required for sensor NLR signalling. TIR-domain-containing sensor NLRs (TNLs) require helper NLRs NRG1 and ADR1 for resistance, and their activation of defense also requires the lipase-domain proteins EDS1, SAG101 and PAD4. We investigated how the helper NLR NRG1 supports TNL-initiated immunity with EDS1 and SAG101. We find that NRG1 associates with EDS1 and SAG101 at the plasma membrane and in the nucleus, but only self-associates at the plasma membrane. Activation of TNLs is sufficient to trigger NRG1-EDS1-SAG101 interaction, but cell-surface receptor-initiated defense is also required to form an oligomeric Resistosome. The data point to formation of NRG1-EDS1-SAG101 heterotrimers in the nucleus upon intracellular receptor activation alone and indicate formation of NRG1-EDS1-SAG101 Resistosomes at the plasma membrane upon co-activation of intracellular and cell surface-receptor pathways.

plant biology↗

bioRxiv2022

Sensor NLR immune proteins activate oligomerization of their NRC helper

Nucleotide-binding domain and leucine-rich repeat (NLR) immune receptors are important components of plant and metazoan innate immunity that can function as individual units or as pairs or networks. Upon activation, NLRs form multiprotein complexes termed resistosomes or inflammasomes. Whereas metazoan paired NLRs, such as NAIP/NLRC4, activate into hetero-complexes, the molecular mechanisms underpinning activation of plant paired NLRs, especially whether they associate in resistosome hetero-complexes is unknown. In asterid plant species, the NLR required for cell death (NRC) immune receptor network is composed of multiple resistance protein sensors and downstream helpers that confer immunity against diverse plant pathogens. Here, we show that pathogen effector-activation of the NLR proteins Rx (confers virus resistance) and Bs2 (confers bacterial resistance) leads to oligomerization of the helper NLR NRC2. Activated Rx does not oligomerize or enter into a stable complex with the NRC2 oligomer and remains cytoplasmic. In contrast, activated NRC2 oligomers accumulate in membrane-associated puncta. We propose an activation-and-release model for NLRs in the NRC immune receptor network. This points to a distinct activation model compared to mammalian paired NLRs.

plant biology↗

bioRxiv2022

Effector-dependent activation and oligomerization of NRC helper NLRs by Rpi-amr3 and Rpi-amr1

Plant pathogens compromise crop yields. Plants have evolved robust innate immunity that depends in part on intracellular Nucleotide-binding, Leucine Rich-Repeat (NLR) immune receptors that activate defense responses upon detection of pathogen-derived effectors. Most "sensor" NLRs that detect effectors require the activity of "helper" NLRs, but how helper NLRs support sensor NLR function is poorly understood. Many Solanaceae NLRs require the NRC (NLR-Required for Cell death) class of helper NLRs. We show here that Rpi-amr3, a sensor NLR from Solanum americanum, detects AVRamr3 from the potato late blight pathogen, Phytophthora infestans, and activates oligomerization of the helper NLR NRC2 into a high-molecular weight resistosome. The NRC2 resistosome also forms upon recognition of P. infestans effector AVRamr1 by another sensor NLR, Rpi-amr1. The ATP-binding motif of Rpi-amr3 is required for NRC2 resistosome formation, but not for interaction with the cognate effector. The NRC2 resistosome can be activated by AVRamr3 homologs from other Phytophthora species. Mechanistic understanding of NRC resistosome formation will underpin engineering crops with durable disease resistance.

plant biology↗

bioRxiv2020

Mutual Potentiation of Plant Immunity by Cell-surface and Intracellular Receptors

The plant immune system involves cell-surface receptors that detect intercellular pathogen-derived molecules, and intracellular receptors that activate immunity upon detection of pathogen-secreted effectors that act inside the plant cell. Surface receptor-mediated immunity has been extensively studied but in authentic interactions between plants and microbial pathogens, its presence impedes study of intracellular receptor-mediated immunity alone. How these two immune pathways interact is poorly understood. Here, we reveal mutual potentiation between these two recognition-dependent defense pathways. Recognition by surface receptors activates multiple protein kinases and NADPH oxidases, whereas intracellular receptors primarily elevate abundance of these proteins. Reciprocally, the intracellular receptor-dependent hypersensitive cell death response is strongly enhanced by activation of surface receptors. Activation of either immune system alone is insufficient to provide effective resistance against Pseudomonas syringae. Thus, immune pathways activated by cell-surface and intracellular receptors mutually potentiate to activate strong defense that thwarts pathogens. By studying the activation of intracellular receptors in the absence of surface receptor-mediated immunity, we have dissected the relationship between the two distinct immune systems. These findings reshape our understanding of plant immunity and have broad implications for crop improvement.

plant biology↗

bioRxiv2019

Estradiol-inducible AvrRps4 expression reveals distinct properties of TIR-NLR-mediated effector-triggered immunity

Plant nucleotide-binding domain, leucine-rich repeat receptor (NLR) proteins play important roles in recognition of pathogen-derived effectors. However, the mechanism by which plant NLRs activate immunity is still largely unknown. The paired Arabidopsis NLRs RRS1-R and RPS4, that confer recognition of bacterial effectors AvrRps4 and PopP2, are well studied, but how the RRS1/RPS4 complex activates early immediate downstream responses upon effector detection is still poorly understood. To study RRS1/RPS4 responses without the influence of cell-surface receptor immune pathways, we generated an Arabidopsis line with inducible expression of effector AvrRps4. Induction does not lead to hypersensitive cell death response (HR) but can induce electrolyte leakage, which often correlates with plant cell death. Activation of RRS1 and RPS4 without pathogens cannot activate mitogen-associated protein kinase cascades, but still activates upregulation of defense genes, and therefore resistance against bacteria.\n\nHighlightInducible expression of AvrRps4 activates RRS1/RPS4-mediated effector-triggered immunity without the presence of pathogens, allowing us to characterise downstream immune responses triggered by TIR-NLRs without cell-surface receptor-mediated immunity.

plant biology↗