Belbahri, Lassaâd

2016-4-21, Singer, David, Lara, Enrique, Steciow, Mónica M., Seppey, Christophe, Noelia, Paredes, Pillonel, Amandine, Tomasz, Oszako, Belbahri, Lassaâd

Oomycete diversity has been generally underestimated, despite their ecological and economic importance. Surveying unexplored natural ecosystems with up-to-date molecular diversity tools can reveal the existence of unsuspected organisms. Here, we have explored the molecular diversity of five microhabitats located in five different oligotrophic peat bogs in the Jura Mountains using a high-throughput sequencing approach (Illumina HiSeq 2500). We found a total of 34 different phylotypes distributed in all major oomycete clades, and comprising sequences affiliated to both well-known phylotypes and members of undescribed, basal clades. Parasitic species, including obligate forms were well-represented, and phylotypes related to highly damaging invasive pathogens (Aphanomyces astaci: X1100 and Saprolegnia parasitica: X1602) were retrieved. Microhabitats differed significantly in their community composition, and many phylotypes were strongly affiliated to free water habitats (pools). Our approach proved effective in screening oomycete diversity in the studied habitat, and could be applied systematically to other environments and other fungal and fungal-like groups.

2001, Roetschi, Alexandra, Si-Ammour, Azeddine, Belbahri, Lassaâd, Mauch, Felix, Mauch-Mani, Brigitte

Arabidopsis accessions were screened with isolates of Phytophthora porri originally isolated from other crucifer species. The described Arabidopsis–Phytophthora pathosystem shows the characteristics of a facultative biotrophic interaction similar to that seen in agronomically important diseases caused by Phytophthora species. In susceptible accessions, extensive colonization of the host tissue occurred and sexual and asexual spores were formed. In incompatible combinations, the plants reacted with a hypersensitive response (HR) and the formation of papillae at the sites of attempted penetration. Defence pathway mutants such as jar1 (jasmonic acid-insensitive), etr1 (ethylene receptor mutant) and ein2 (ethylene-insensitive) remained resistant towards P. porri. However, pad2, a mutant with reduced production of the phytoalexin camalexin, was hyper-susceptible. The accumulation of salicylic acid (SA) and PR1 protein was strongly reduced in pad2. Surprisingly, this lack of SA accumulation does not appear to be the cause of the hyper-susceptibility because interference with SA signalling in nahG plants or sid2 or npr1 mutants had only a minor effect on resistance. In addition, the functional SA analogue benzothiadiazol (BTH) did not induce resistance in susceptible plants including pad2. Similarly, the complete blockage of camalexin biosynthesis in pad3 did not cause susceptibility. Resistance of Arabidopsis against P. porri appears to depend on unknown defence mechanisms that are under the control of PAD2.

, Pawlowski, Jan, Audic, Stéphane, Adl, Sina, Bass, David, Belbahri, Lassaâd, Berney, Cédric, Bowser, Samuel S., Cepicka, Ivan, Decelle, Johan, Dunthorn, Micah, Fiore-Donno, Anna Maria, Gile, Gillian H., Holzmann, Maria, Jahn, Regine, Jirků, Miloslav, Keeling, Patrick J., Kostka, Martin, Kudryavtsev, Alexander, Lara, Enrique, Lukeš, Julius, Mann, David G., Mitchell, Edward, Nitsche, Frank, Romeralo, Maria, Saunders, Gary W., Simpson, Alastair G. B., Smirnov, Alexey V., Spouge, John L., Stern,Rowena F., Stoeck, Thorsten, Zimmermann, Jonas, Schindel, David, de Vargas, Colomban

2012, Pawlowski, Jan, Audic, Stephane, Adl, Sina M., Bass, David, Belbahri, Lassaâd, Berney, Cedric, Bowser, Samuel S., Cepicka, Ivan, Decelle, Johan, Dunthorn, Micah, Fiore-Donno, Anna Maria, Gile, Gillian H., Holzmann, Maria, Jahn, Regine, Jirku, Miloslav, Keeling, Patrick J., Kostka, Martin, Kudryavtsev, Alexander, Lara, Enrique, Lukes, Julius, Mann, David G., Mitchell, Edward, Nitsche, Frank, Romeralo, Maria, Saunders, Gary W., Simpson, Alastair G. B., Smirnov, Alexey V., Spouge, John L., Stern, Rowena F., Stoeck, Thorsten, Zimmermann, Jonas, Schindel, David, de Vargas, Colomban

2001, Roetschi, Alexandra, Si-Ammour, Azeddine, Belbahri, Lassaâd, Mauch, Felix, Mauch-Mani, Brigitte

, Steciow, Mónica M, Lara, Enrique, Pillonel, Amandine, Pelizza, Sebastián A, Lestani, Eduardo A, Rossi, Gustavo C, Belbahri, Lassaâd

The genus Geolegnia represents a poorly documented group of saprolegnialean oomycetes isolated from soils as free-living organisms. Although it is morphologically similar to the facultative parasitic genus Leptolegnia, Geolegnia presents the uncommon property of having lost a flagellate stage in its lifecycle. Based on ITS and large subunit (LSU) rRNA sequence data, we show Geolegnia to be basal to Leptolegnia, and also introduce Geolegnia helicoides sp. nov. Using sequence data of Leptolegnia available in GenBank, supplemented by data derived from culture collections, we show that Geolegnia is nested within Leptolegnia, a genus characterised by its “conventional” biflagellate life cycle. The emergence of Geolegnia is therefore seen as a recent event, and we suggest here an evolutionary context where this loss might have been advantageous. Based on this study, Leptolegnia remains paraphyletic, awaiting the redefinition of genera in this complex.

2011, Lara, Enrique, Belbahri, Lassaâd

Oomycetes are a group of heterokonts that have a huge impact on the environment as well as on human welfare, due the parasitic nature of many species. However, their evolutionary patterns are still not well understood, due in part to the lack of molecular markers suited to resolve the deep phylogeny of this group. Here, we propose a phylogeny of the whole clade based on the nuclear ribosomal small subunit gene, that comprises both culture and environmental studies derived sequences. Our analysis shows notably that i) plant pathogenesis occurred only rarely in oomycete evolution in comparison to animal parasitism ii) obligate symbiosis happened only in a few derived groups and iii) transitions from soil/freshwater to marine environment (and viceversa) are common unlike for most eukaryotic groups. This study illustrates the complexity of evolutionary patterns and will help to better understand the emergence of pathogenicity in the different oomycete groups.

, Geisen, Stefan, Mitchell, Edward, Wilkinson, David M, Adl, Sina, Bonkowski, Michael, Brown, Matthew W, Fiore-Donno, Anna Maria, Heger, Thierry, Jassey, Vincent E.J, Krashevska, Valentyna, Lahr, Daniel J.G, Marcisz, Katarzyna, Mulot, Matthieu, Payne, Richard, Singer, David, Anderson, Roger O, Charman, Dan J, Ekelund, Flemming, Griffiths, Bryan S, Rønn, Regin, Smirnov, Alexey, Bass, David, Belbahri, Lassaâd, Berney, Cédric, Blandenier, Quentin, Blandenier, Quentin, Chatzinotas, Antonis, Clarholm, Marianne, Dunthorn, Micah, Feest, Alan, Fernández, Leonardo D, Foissner, Wilhelm, Fournier, Bertrand, Gentekaki, Eleni, Hájek, Michal, Helder, Johannes, Jousset, Alexandre, Koller, Robert, Kumar, Santosh, La Terza, Antonietta, Lamentowicz, Mariusz, Mazei, Yuri, Santos, Susana S, Seppey, Christophe V.W, Spiegel, Frederick W, Walochnik, Julia, Winding, Anne, Lara, Enrique

Protists are the most diverse eukaryotes. These microbes are keystone organisms of soil ecosystems and regulate essential processes of soil fertility such as nutrient cycling and plant growth. Despite this, protists have received little scientific attention, especially compared to bacteria, fungi and nematodes in soil studies. Recent methodological advances, particularly in molecular biology techniques, have made the study of soil protists more accessible, and have created a resurgence of interest in soil protistology. This ongoing revolution now enables comprehensive investigations of the structure and functioning of soil protist communities, paving the way to a new era in soil biology. Instead of providing an exhaustive review, we provide a synthesis of research gaps that should be prioritized in future studies of soil protistology to guide this rapidly developing research area. Based on a synthesis of expert opinion we propose 30 key questions covering a broad range of topics including evolution, phylogenetics, functional ecology, macroecology, paleoecology, and methodologies. These questions highlight a diversity of topics that will establish soil protistology as a hub discipline connecting different fundamental and applied fields such as ecology, biogeography, evolution, plant-microbe interactions, agronomy, and conservation biology. We are convinced that soil protistology has the potential to be one of the most exciting frontiers in biology.