Biology subjects

Ollivier, B.

Publications and source records attributed to Ollivier, B..

5 recordsLinked to original sources

bioRxiv2025

Molecular investigation of Rlm3 from rapeseed as a broad-spectrum resistance gene against fungal pathogens producing structurally conserved effectors

Recognition of a pathogen avirulence (AVR) effector protein by its cognate plant resistance (R) protein triggers immune responses that render the plant resistant, representing an efficient disease control strategy. While (AVR) effectors have long been considered species- or genotype-specific, based on a lack of homology in sequence databases, a growing number of studies have now shown that these proteins belong to a limited set of structural families. This is an important finding because it paves the way for the identification or engineering of broad- spectrum R proteins capable of recognizing several members of the same structural family. In the Leptosphaeria maculans / rapeseed (Brassica napus) pathosystem, 13 AVR genes have been cloned, of which four encode effectors belonging to the LARS (Leptosphaeria AviRulence and Supressing) structural family that has also been found in thirteen other phytopathogenic fungi. Homologues of the L. maculans AvrLm3 AVR protein, a LARS family member, have been identified in other fungal species, including an AVR protein from Fulvia fulva called Ecp11-1. We have previously shown that Ecp11-1 is recognized by rapeseed varieties carrying the Rlm3 R gene, and that this recognition is masked by the presence of another LARS AVR gene, AvrLm4-7. In this study, we expanded our characterization of the Rlm3 resistance spectrum to putative effectors from Fusarium oxysporum and Zymoseptoria ardabiliae and showed that one effector from F. oxysporum f. sp. narcissi behaves like Ecp11-1, being recognized by Rlm3, and this recognition also being masked by the presence of AvrLm4-7. We finally investigated which protein regions and amino acids were necessary for the recognition of AvrLm3 and Ecp11-1 by Rlm3. This analysis is a first step towards the identification or engineering of broad- spectrum R proteins that confer protection against multiple phytopathogens through the recognition of structural effector families.

plant biology↗

bioRxiv2023

Predicting hERG repolarization power at 37°C from recordings at room temperature

Mutations in the KCNH2 gene cause long or short QT syndromes (LQTS or SQTS) predisposing to life-threatening arrhythmias. KCNH2 encodes for the voltage-gated K+ channel hERG involved in the late repolarization phase of the cardiac action potential (AP). For the last decades, sequencing KCNH2 has provided a plethora of variants associated or not with clear pathological cardiac phenotypes. Identifying pathogenic or likely pathogenic variants from the benign ones would provide useful information to clarify the genetic background of LQTS patients and relatives, and to stratify the risk of adverse events. In face of a wide spectrum of hERG biophysical defects, we looked for a way to summarize the net loss or gain of function in a unique index. In a previous work, we defined as the repolarization power the time integral of the K+ currents developed during an AP clamp. Here, with the aim of accelerating the functional characterization of hERG variants using automated patch-clamp, we adapted the AP-clamp protocol to establish, at room temperature, at which the recording success rate is high, a repolarization power index, as reliable and informative as the one measured at physiological temperature. We also illustrate that the repolarization power determined at room temperature is predictive of the repolarization power at physiological temperature for 2 pathogenic hERG variants with different biophysical dysfunctions.

physiology↗

bioRxiv2022

SARS-CoV2 E and 3a proteins are inducers of pannexin currents

Controversial reports have suggested that SARS-CoV E and 3a proteins may be viroporins that conduct currents through the plasma membrane of the infected cells. If true, these proteins would represent accessible targets for the development of new antiviral drugs by using high-throughput patch-clamp techniques. Here we aimed at better characterizing the cell responses induced by E or 3a protein with a particular focus on the ion conductances measured at the cell surface. First, we show that expression of SARS-CoV-2 E or 3a protein in CHO cells gives rise to cells with newly-acquired round shape, tending to detach from the Petri dish. This suggests that cell death is induced upon expression of E or 3a protein. We confirmed this hypothesis by using flow cytometry, in agreement with earlier reports on other cell types. In adhering cells expressing E or 3a protein, whole-cell currents were in fact not different from the control condition indicating that E and 3a proteins are not plasma membrane viroporins. In contrast, recording currents on detached cells uncovered outwardly-rectifying currents, much larger than those observed in control. The current characteristics are reminiscent of what was previously observed in cells expressing SARS-CoV-1 E or 3a proteins. Herein, we illustrate for the first time that carbenoxolone blocks these outward currents suggesting that they are conducted by pannexin channels, mostly likely activated by cell morphology change and/or cell death. Alongside we also demonstrate that truncation of the C-terminal PDZ binding motifs reduces the proportion of dying cells but does not prevent pannexin currents suggesting distinct pathways for cell death and pannexin currents induced by E and 3a proteins. We conclude that SARS-CoV-2 E and 3a proteins are not acting as viroporins expressed at the plasma membrane. Author SummaryA viroporin (or viral porin) is a class of proteins that is encoded by a virus genome. It is named porin because its biological role is to conduct ions through a pore that it created in a lipid membrane such as the one surrounding a human cell. if such viroporin is present at the external membrane of a human cell infected by a virus, it can be an easy target of an antiviral agent which thus does not have to enter the cell to be active. One example of viroporin is the flu M2 protein that is the target of amantadine, an antiviral agent used against flu. In previous studies, two proteins of SARS-CoV viruses, named E protein and 3a protein, have been suggested to be viroporins at the surface of infected human cells, potentially opening a new research avenue against SARS. Here we demonstrate that both proteins are not viroporins at the external membrane but they rather trigger changes in the cell shape and promote cell death. They only indirectly induce the activity of a porin that is encoded by the cell genome, named pannexin.

cell biology↗

bioRxiv2020

A new family of structurally conserved fungal effectors displays epistatic interactions with plant resistance proteins

Recognition of a pathogen avirulence (AVR) effector protein by a cognate plant resistance (R) protein triggers a set of immune responses that render the plant resistant. Pathogens can escape this so-called Effector-Triggered Immunity (ETI) by different mechanisms including the deletion or loss-of-function mutation of the AVR gene, the incorporation of point mutations that allow recognition to be evaded while maintaining virulence function, and the acquisition of new effectors that suppress AVR recognition. The Dothideomycete Leptosphaeria maculans, causal agent of oilseed rape stem canker, is one of the few fungal pathogens where suppression of ETI by an AVR effector has been demonstrated. Indeed, AvrLm4-7 suppresses Rlm3- and Rlm9- mediated resistance triggered by AvrLm3 and AvrLm5-9, respectively. The presence of AvrLm4-7 does not impede AvrLm3 and AvrLm5-9 expression, and the three AVR proteins do not appear to physically interact. To decipher the epistatic interaction between these L. maculans AVR effectors, we determined the crystal structure of AvrLm5-9 and obtained a 3D model of AvrLm3, based on the crystal structure of Ecp11-1, a homologous AVR effector candidate from Fulvia fulva. Despite a lack of sequence similarity, AvrLm5-9 and AvrLm3 are structural analogues of AvrLm4-7 (structure previously characterized). Structure-informed sequence database searches identified a larger number of putative structural analogues among L. maculans effector candidates, including the AVR effector AvrLmS-Lep2, all produced during the early stages of oilseed rape infection, as well as among effector candidates from other phytopathogenic fungi. These structural analogues are named LARS (for Leptosphaeria AviRulence and Suppressing) effectors. Remarkably, transformants of L. maculans expressing one of these structural analogues, Ecp11-1, triggered oilseed rape immunity in several genotypes carrying Rlm3. Furthermore, this resistance could be suppressed by AvrLm4-7. These results suggest that Ecp11-1 shares a common activity with AvrLm3 within the host plant which is detected by Rlm3, or that the Ecp11-1 structure is sufficiently close to that of AvrLm3 to be recognized by Rlm3. Author summaryAn efficient strategy to control fungal diseases in the field is genetic control using resistant crop cultivars. Crop resistance mainly relies on gene-for-gene relationships between plant resistance (R) genes and pathogen avirulence (AVR) genes, as defined by Flor in the 1940s. However, such gene-for-gene relationships can increase in complexity over the course of plant-pathogen co-evolution. Resistance against the plant-pathogenic fungus Leptosphaeria maculans by Brassica napus and other Brassica species relies on the recognition of effector (AVR) proteins by R proteins; however, L. maculans produces an effector that suppresses a subset of these specific resistances. Using a protein structure approach, we revealed structural analogy between several of the resistance-triggering effectors, the resistance-suppressing effector, and effectors from other plant-pathogenic species in the Dothideomycetes and Sordariomycetes classes, defining a new family of effectors called LARS. Notably, cross-species expression of one LARS effector from Fulvia fulva, a pathogen of tomato, in L. maculans resulted in recognition by several resistant cultivars of oilseed rape. These results highlight the need to integrate knowledge on effector structures to improve resistance management and to develop broad-spectrum resistances for multi-pathogen control of diseases.

plant biology↗

bioRxiv2020

Two independent approaches converge to the cloning of a new Leptosphaeria maculans avirulence effector gene, AvrLmS-Lep2

Leptosphaeria maculans, the causal agent of blackleg disease, interacts with Brassica napus (oilseed rape, canola) in a gene-for-gene manner. The avirulence genes AvrLmS and AvrLep2 were described to be perceived by the resistance genes RlmS and LepR2, respectively, present in the cultivar Surpass 400. Here we report cloning of AvrLmS and AvrLep2 using two independent methods. AvrLmS was cloned using combined in vitro crossing between avirulent and virulent isolates with sequencing of DNA bulks from avirulent or virulent progeny (Bulked-Segregant-Sequencing) to rapidly identify one candidate avirulence gene present in the effector repertoire of L. maculans. AvrLep2 was cloned using a bi-parental cross of avirulent and virulent L. maculans isolates and a classical map-based cloning approach. Taking these two approaches independently, we found that AvrLmS and AvrLep2 are the same gene. Complementation of virulent isolates with this gene confirmed its role in inducing resistance on Surpass 400 and Topas-LepR2. The gene renamed AvrLmS-Lep2 encodes for a small cysteine-rich protein of unknown function with an N-terminal secretory signal peptide, which are common features of the majority of effectors from extracellular fungal plant pathogens. The AvrLmS-Lep2 / LepR2 interaction phenotype was found to vary from a typical hypersensitive response to intermediate resistance sometimes at the edge of, or evolving toward, susceptibility depending on the inoculation conditions. AvrLmS-Lep2 was nevertheless sufficient to significantly reduce the stem lesion size on plant genotypes with LepR2, indicating the potential efficiency of this resistance to control the disease in the field.

molecular biology↗