Biology subjects

McLellan, H.

Publications and source records attributed to McLellan, H..

4 recordsLinked to original sources

bioRxiv2025

PaRXLR40, a broad cell death suppressor of the kauri dieback pathogen Phytophthora agathidicida, targets a plant ARM/BTB domain-containing protein

O_LIPhytophthora agathidicida, the causal agent of kauri dieback, secretes RXLR effector proteins to promote host colonisation. One of these, PaRXLR40, was previously shown to suppress immune responses in Nicotiana benthamiana, but its mechanism of action and contribution to virulence remained unclear. C_LIO_LITo investigate PaRXLR40 function, we used comparative approaches in N. benthamiana and Agathis australis (kauri), including RNA interference (RNAi), transient expression assays, confocal microscopy, yeast two-hybrid screens, and infection assays. We also examined host protein interactors and tested mutant variants to evaluate functional domains. C_LIO_LISilencing PaRXLR40 reduced P. agathidicida colonization in N. benthamiana and A. australis. PaRXLR40 interacted with a host BTB/ARM domain protein (ARIA), previously implicated in abscisic acid (ABA) signalling. ARIA suppressed immunity and promoted infection, while interacting with NbSOG1, a DNA damage-associated transcription factor that enhanced resistance when overexpressed. External application of ABA enhanced P. agathidicida infection in both hosts, supporting the hypothesis that PaRXLR40 may hijack host ABA signalling through ARIA to promote susceptibility. C_LIO_LIOur findings show that PaRXLR40 targets ARIA to manipulate host immunity and promote virulence. The interaction between ARIA and SOG1 suggests PaRXLR40 may interfere with host transcriptional reprogramming. PaRXLR40 represents a potential target for future RNAi-based strategies to reduce kauri dieback. C_LI

molecular biology↗

bioRxiv2025

Transcriptional response to Phytophthora root rot in raspberry identifies RiABP19, a Germin-like protein (GLP) gene with a putative role in resistance

Most phytophthora root rot (PRR) outbreaks in symptomatic commercially cultivated raspberry varieties are associated with the prevalence of Phytophthora rubi. Reduced availability of chemical actives and the persistent presence of Phytophthora oospores in the soil contribute to its devastating impact on raspberry-growing regions. In this study, we examined the variation in root morphology in two contrasting raspberry cultivars, Latham (PRR resistant) and Glen Moy (PRR susceptible). We performed RNA-sequencing on Latham roots challenged with P. rubi, to study the transcriptomic response and uncover mechanisms underpinning resistance. We established a new raspberry reference transcript dataset that allowed quantification of raspberry root gene expression. Transcripts significantly upregulated in Latham challenged with P. rubi, included many with characterised roles in resistance, such as Pathogenesis-related proteins and a Germin-like protein, designated RiABP19. The homologous Glen Moy RiABP19 gene showed no differential transcriptional response to PRR infection, indicating a resistance cultivar-specific induction signature following PRR challenge. Three-dimensional structural modelling predicts that RiABP19 contains conserved active sites implicated in auxin-binding and superoxide dismutase activity and can form a homo-hexamer like true germins. Co-immunoprecipitation assays confirmed that RiABP19 can form both homo- and heterodimers in planta. Virus-induced gene silencing of RiABP19 orthologs of in the model plant Nicotiana benthamiana strongly impacts immune signalling, enhancing Phytophthora infestans colonization and attenuating resistance and cell death triggered by the tomato Cf4/Avr4 interaction. These findings suggest that RiABP19 functions as a positive regulator of immunity and may represent a target for future crop improvement in raspberries.

plant biology↗

bioRxiv2025

Identification of MARVELlous Protein Markers for Phytophthora infestans Extracellular Vesicles

Extracellular vesicles (EVs) are released from cells by unconventional secretion, but little is known about the biogenesis routes, composition or cargoes of EVs from fungal or oomycete plant pathogens. We investigated the proteome of EV-associated proteins secreted by the oomycete Phytophthora infestans, cause of potato late blight disease. We found that vesicle-associated proteins, transmembrane proteins and RxLR effectors, which are delivered into host cells to suppress immunity, were enriched in the EV proteome. By contrast, the EV-independent secreted proteome was enriched in cell wall modifying enzymes and apoplastic effectors which act outside plant cells. Two proteins each containing two tetraspanning MARVEL domains, PiMDP1 and PiMDP2, were associated with P. infestans EVs. PiMDP1 and PiMDP2 were co-buoyant with RxLR effectors in sucrose density fractions containing EVs and co-localised frequently with each other and with RxLRs at vesicles within pathogen hyphae grown in vitro and during infection. Interestingly, PiMDP2, which is up-regulated during the early biotrophic phase of infection, accumulates at the haustorial interface, a major site of effector secretion during infection. We argue that PiMDP1 and PiMDP2 are molecular markers that will facilitate studies of the biogenesis and secretion of infection-associated P. infestans EVs.

plant biology↗

bioRxiv2020

The plant endoplasmic reticulum is both receptive and responsive to pathogen effectors

The endoplasmic reticulum (ER) is the entry point to the secretory pathway and, as such, is critical for adaptive responses to biotic stress, when the demand for de novo synthesis of immunity-related proteins and signalling components increases significantly. Comprised of a network of interconnected tubules and cisternae, the architecture of the ER is highly pleomorphic and dynamic, rapidly remodelling to meet new cellular requirements. During infection with the hemi-biotrophic phytopathogen, Pseudomonas syringae pv. tomato DC3000, the ER in cells immediately adjacent to established bacterial colonies condenses into knot-like structures, reminiscent of fenestrated sheets. Based on known temporal dynamics of pathogen effector delivery and initial bacterial multiplication, the timing of these observed morphological changes is rapid and independent of classical elicitor activation of pathogen-triggered immunity. To further investigate a role for ER reconfiguration in suppression of plant immunity we identified a conserved C-terminal tail-anchor domain in a set of pathogen effectors known to localize to the ER and used this protein topology in an in silico screen to identify putative ER-localised effectors within the effectorome of the oomycete Phytophthora infestans. Subsequent characterization of a subset of 15 candidate tail-anchored P. infestans effectors revealed that 11 localised to the ER and/or Golgi. Notably, transient expression of an ER-localised effector from the closely related oomycete, Plasmopara halstedii, reconfigured the ER network, revealing intimate association of labelled ER with perinuclear chloroplasts and clusters of chloroplasts, potentially facilitating retrograde signalling during plant defence.

plant biology↗