Biology subjects

Thordal-Christensen, H.

Publications and source records attributed to Thordal-Christensen, H..

6 recordsLinked to original sources

bioRxiv2026

Powdery mildew fungi block plant vacuolar traffic to suppress immunity

Plant immunity can be activated by membrane-localized pattern recognition receptors or by cytosolic nucleotide-binding leucine-rich repeat (NLR) receptors, while it can be counteracted by pathogen secreted effectors. Manifestation of immunity often involves endomembrane traffic. However, limited evidence is available for such an involvement in NLR-mediated immunity, which typically includes a hypersensitive reaction (HR)-programmed cell death response. Here we show that the barley powdery mildew fungus uses several effectors to target and inhibit the vacuolar trafficking pathway, which causes endomembrane markers to stall in the endoplasmic reticulum (ER). We used this ER-stalling phenotype as a proxy to track fungal manipulation of the vacuolar pathway during different stages of the actual infection. Our data indicate that powdery mildew fungi interfere with the vacuolar pathway, but only temporarily, as the stalling is lifted once the fungal haustorial feeding structures are well-developed for nutrient uptake in epidermal cells. Notably, we show evidence that blocking the vacuolar pathway causes a general inhibition of NLR-mediated HR, and that this mechanism is taken advantage of by the pathogen. Finally, we provide an example that the fungus can secrete a different set of effectors at the haustorial stage that result in the re-opening of the vacuolar pathway by inhibiting the initial vacuolar traffic-suppressing effectors.

plant biology↗

bioRxiv2025

Molecular Insights into the Production of Extracellular Vesicles by Plants

Extracellular vesicles (EVs) produced by Arabidopsis are highly heterogeneous in protein content. Specific EV subpopulations have been proposed to participate in plant immunity, particularly during plant-fungal interaction. To understand the origins of plant EV heterogeneity, we used a proximity labeling approach to identify proteins and pathways involved in the secretion of distinct EV subpopulations. Proximity labeling, co-immunoprecipitation, and fluorescence microscopy in Nicotiana benthamiana all indicated a general role in EV secretion for EXO70 proteins (a subunit of the exocyst complex) and the immune-related protein RPM1-INTERACTING PROTEIN 4 (RIN4), while the ER-localized VAMP-ASSOCIATED PROTEIN 27(VAP27) was specifically associated with the EV marker protein TETRAPSANIN8 (TET8). Despite being secreted in separate EV populations, we found that TET8 and PENETRATION 1 (PEN1) co-localized in multivesicular body-like subcellular structures. Based on these results, we tested Arabidopsis mutants and identified several proteins involved in EV secretion, including members of the exo70 family, rin4, rabA2a, scd1 (a GTP-exchange factor for RabE GTPases), and vap27. We also uncovered a possible connection between trichomes and EVs, as the trichomeless mutant glabrous1 secreted approximately half the number of EVs as wild type. Furthermore, PEN1 MVB-like structures were prevalent in guard cells, suggesting that guard cells may contribute to secretion of PEN1+ EVs on the leaf surface. Lastly, we found that exo70 family mutants are more susceptible to infection with the fungal pathogen Colletotrichum higginsianum, underlining the importance of secretion for plant immunity. Together, our results unravel some of the complex mechanisms that give rise to EV subpopulations in plants.

plant biology↗

bioRxiv2024

A powdery mildew core effector protein targets host endosome tethering complexes HOPS and CORVET

Powdery mildew fungi are serious pathogens of many plant species. Their genomes encode extensive repertoires of secreted effector proteins that suppress host immunity. Here, we revised and analyzed the candidate secreted effector protein (CSEP) effectome of the barley powdery mildew fungus, Blumeria hordei (Bh) and identified seven CSEPs that are broadly conserved in powdery mildew fungal species, rendering them core effectors of these phytopathogens. We show that one of these, CSEP0214, interacts with the barley VPS18 protein, a core component of the CORVET and HOPS endosomal tethering complexes, mediating fusions of early endosomes and multivesicular bodies with the central vacuole, respectively. Overexpression of CSEP0214 and knockdown of either VPS18, HOPS-specific VPS41 or CORVET-specific VPS8 caused a block of the vacuolar pathway and the accumulation of the fluorescent vacuolar marker protein (SP)-RFP-AFVY in the endoplasmic reticulum. Co-immunoprecipitation and yeast two-hybrid experiments suggest that CSEP0214 blocks the interaction of VPS18 and VPS16, which are both core components of CORVET as well as HOPS. Additionally, expression of CSEP0214 blocked the hypersensitive cell death response associated with resistance gene-mediated immunity in barley, indicating that endomembrane traffic is required for this process. It also prevented callose deposition in cell wall appositions at attack sites and encasements of fungal infection structures. Our results indicate that this powdery mildew core effector is an essential immunity suppressor. One sentence summaryThe Blumeria hordei effector protein CSEP0214 interacts with barley VPS18, a core component of the CORVET and HOPS endosomal tethering complexes, thereby interfering with host endomembrane trafficking.

plant biology↗

bioRxiv2024

A frosty genetic screen unmasks a major regulatory role for SHORT VEGETATIVE PHASE of flowering in response to a cold snap

The control of flowering in plants is intricately governed by a combination of internal and environmental signals, with temperature playing a critical role. Thus, Arabidopsis thaliana plants display temperature-dependent variations in flowering time. As unexpected periods of cold temperatures can occur at any time, plants have evolved mechanisms to detect such cold snaps and to respond by delaying flowering. Plants are more tolerant to cold temperatures in the vegetative stage, while flowers are more sensitive and have reduced reproductive success due to damage to floral structures and gametes. At the molecular level, delayed flowering can be caused by repressing the FLOWERING LOCUS T (FT) gene, and several MADS box transcription factors have been shown to repress FT expression in response to cold and in this way prevent flowering. Here, we employed a forward genetic screen aimed at understanding the effect of a cold snap on the transition to flowering. We germinated a population of A. thaliana EMS M2 plants at 20{degrees}C and then gradually lowered the temperature to 10{degrees}C and selected early flowering mutants. Using whole-genome sequencing, we identified seven mutant alleles of the SHORT VEGETATIVE PHASE (SVP) gene. This finding establishes a central role for SVP in repressing flowering in response to a cold snap and provides novel alleles, several of which affect splice junctions. Our research thus presents valuable insights into the nuanced molecular mechanisms governing temperature-responsive flowering in Arabidopsis and sheds light on the dynamic interplay between SVP and environmental cues.

plant biology↗

bioRxiv2022

Barley powdery mildew effector CSEP0162 targets multivesicular body-associated MON1 important for immunity

Encasements formed around haustoria and biotrophic hyphae as well as hypersensitive reaction (HR) cell death are essential plant immune responses to filamentous pathogens. Here we study a possible reason why these responses are absent in susceptible barley attacked by the powdery mildew fungus. We find that the effector CSEP0162 from this pathogen targets plant MON1, important for fusion of multivesicular bodies to their target membranes. Over-expression of CSEP0162 and silencing of barley MON1 both inhibit encasement formation. We find that the Arabidopsis ecotype No-0 has partial resistance to powdery mildew, and that this is dependent on MON1. Surprisingly, we find the MON1-dependent resistance in No-0 not only include an effective encasement response, but also HR. Similarly, silencing of MON1 in barley also blocked Mla3-mediated HR-based powdery mildew resistance. These data indicate that MON1 is a vital plant immunity component, and we speculate that the barley powdery mildew fungus introduces the effector CSEP0162 to target MON1 and reduce encasement formation and HR. HighlightMON1 is essential for MVB fusion to plasma membrane. We find that MON1 also is important for immunity, and that it is targeted by the barley powdery mildew effector CSEP0162.

plant biology↗

bioRxiv2022

Powdery mildew effectors AVRA1 and BEC1016 target the ER J-domain protein HvERdj3B required for immunity in barley

The barley powdery mildew fungus, Blumeria hordei (Bh), secretes hundreds of candidate secreted effector proteins (CSEPs) to facilitate pathogen infection and colonization. One of these, CSEP0008, is directly recognized by the barley nucleotide-binding leucine-rich-repeat (NLR) receptor, MLA1, and therefore designated AVRA1. Here we show that AVRA1 and the sequence-unrelated Bh effector BEC1016 (CSEP0491) suppress immunity in barley. We used yeast two-hybrid next-generation interaction screens (Y2H-NGIS), followed by binary Y2H and in planta protein-protein interactions studies, and identified a common barley target of AVRA1 and BEC1016, the endoplasmic reticulum (ER)-localized J-domain protein, HvERdj3B. Silencing of this ER quality control (ERQC) protein increased the Bh penetration. HvERdj3B is ER luminal, and we showed using split GFP that AVRA1 and BEC1016 translocate into the ER - signal peptide-independently. Silencing of HvERdj3B and expression the two effectors hampered trafficking of a vacuolar marker through the ER as a shared cellular phenotype, agreeing with the effectors targeting this ERQC component. Together, these results suggest that the barley innate immunity, preventing Bh entry into epidermal cells, is dependent on ERQC, which in turn requires the J-domain protein, HvERdj3B, regulated by AVRA1 and BEC1016. Plant disease resistance often occurs upon direct or indirect recognition of pathogen effectors by host NLR receptors. Previous work has shown that AVRA1 is directly recognized in the cytosol by the immune receptor, MLA1. We speculate that the AVRA1 J-domain target being inside the ER, where it is inapproachable by NLRs, has forced the plant to evolve this challenging direct recognition. SIGNIFICANCEThe complex plant immune system is highly dependent on fundamental cellular machineries, such as the endomembrane system and the ER quality control (ERQC), essential for delivery of immunity-associated membrane-bound and endomembrane soluble proteins to their destinations. We now find that pathogen effectors can interact with an ERQC component and suppress immunity, thereby adding to the molecular insight in plant-pathogen interactions.

plant biology↗