Search bioRxiv⌕ Search

Biology subjects

Koch, B. L.

Publications and source records attributed to Koch, B. L..

4 recordsLinked to original sources

Extracellular vesicles associate with infectious geminiviral particles in the apoplast of infected plants.

Plant viruses have evolved diverse strategies to facilitate their movement and survival within the host. Among them, geminiviruses co-opt host cellular machinery to replicate and disseminate. Traditionally, viral propagation has been associated with intercellular symplastic trafficking mediated by plasmodesmata and viral movement proteins. However, recent evidence demonstrated that the plant RNA virus turnip mosaic virus (TuMV) components are associated with extracellular vesicles (EVs). EVs are membrane-bound structures secreted to the extracellular space to potentially mediate several plant-pathogen interactions such as cross-kingdom RNA interference or the delivery of stress response proteins. In animals, EVs facilitate viral transmission both within the host and across species, but knowledge about their potential roles in plant viral infection is scarce. In this study, we demonstrate that EVs isolated from geminivirus-infected plants contain complete viral genomes and both capsid and viral movement proteins. Furthermore, these EV fractions were demonstrated to be infectious when mechanically inoculated onto naive plants. This discovery suggests that EVs may serve as alternative carriers for geminivirus components, enabling long-range transport or potentially modulating host immune responses, and highlights geminiviral capacity to transverse membrane boundaries, essential for circulative arbovirus propagation in their insect vectors. Significance StatementViruses are obligate intracellular parasites that shape ecological communities and crucially challenge animal and plant health worldwide. Conversely to animal viruses, plant-infecting viruses rely on plasmodesmata to disseminate through their host and establish systemic infection. Nonetheless, most plant viruses are insect-transmitted whose ecological cycle relies on their insect vector spread. Thus, strategies to cross continuous membrane barriers are essential for their dissemination and may be potentially conserved in plant hosts. Our discovery that infectious viral entities are associated with EVs reveals an alternative pathway for geminiviral movement within plant hosts that could facilitate vector transmission, challenging our long-standing understanding of plant virus biology and expanding the current conception of plant viral pathology.

plant biology↗

A specialized ARGONAUTE enables trans-species RNA interference in plant immunity

Trans-species RNA interference (tsRNAi), in which plants produce small RNAs (sRNAs) to silence target genes in pathogens, has emerged as a promising strategy for disease control. However, whether tsRNAi constitutes an endogenous, regulated immune response remains unclear. Here, we show that ARGONAUTE10 (AGO10) plays a critical role in pathogen-induced tsRNAi. Loss of AGO10 in Arabidopsis abolished pathogen gene silencing during infection, leading to hypersusceptibility to oomycete and fungal pathogens. Importantly, AGO10 rapidly responds to pathogen infection through increased protein accumulation and re-location into discrete cytoplasmic condensates, thus promoting the production of trans-species sRNAs at the pathogen infection sites. This immune responsiveness relies on the N terminal intrinsically disordered region (IDR) of AGO10, which is responsible for sensing and responding to immune activation. Specific features in the IDR partitions AGO10 into two deeply diverged subgroups, AGO10a and AGO10b, with the immune responsiveness and defense function evolutionarily conserved in AGO10a but not AGO10b. Together, these findings establish tsRNAi as a bona fide, evolutionarily conserved immune response and position AGO10 as a signal-responsive hub linking pathogen perception to tsRNAi-based defense.

plant biology↗

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↗

Arabidopsis produces distinct subpopulations of extracellular vesicles that respond differentially to biotic stress

Extracellular vesicles (EVs) secreted by mammalian cells are highly heterogenous in contents and function. Whether this is also true for EVs secreted by plant cells is not yet known. To address this knowledge gap, we used high-resolution density gradient ultracentrifugation to separate distinct subpopulations of Arabidopsis EVs. We analyzed the protein content, morphology, and purity of these subpopulations, confirming the presence of three distinct EV subpopulations. The EV marker protein TETRASPANIN 8 (TET8) was detected only in medium-density EVs and was not associated with cell wall nanofilaments, which was unique among EV proteins. TET8 and PENETRATION 1 (PEN1) were confirmed to be secreted on mostly separate EV populations using total internal fluorescence microscopy. We found that EV marker proteins are differentially secreted in response to phytohormones, changes in growth temperature, and infection with fungal pathogens Colletotrichum and Golovinomyces cichoracearum. EV subpopulations marked by TET8, PEN1, and RPM1-INTERACTING PROTEIN 4 (RIN4) were highly increased as soon as one day after fungal infection, while other EV populations remained unaffected. Together these data indicate that Arabidopsis EVs are highly heterogenous and suggest that specific EV subpopulations may contribute to plant immunity.

plant biology↗