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Mariehelene Balesdent - One of the best experts on this subject based on the ideXlab platform.
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fitness cost associated with loss of the avrlm4 avirulence function in leptosphaeria maculans phoma stem canker of oilseed rape
European Journal of Plant Pathology, 2006Co-Authors: Yongju Huang, Bruce D L Fitt, Ziqin Li, N Evans, Thierry Rouxel, Mariehelene BalesdentAbstract:Near-isogenic isolates of Leptosphaeria maculans differing at the AvrLm4 avirulence locus (AvrLm4 or avrLm4) were produced in vitro. Methods for inoculation of leaves of oilseed rape with Ascospores or conidia were compared. The ‘Ascospore shower’ inoculation was the most efficient method for use when inoculum is limited (e.g. Ascospores produced in vitro). It was used in controlled environments to compare fitness of AvrLm4 and avrLm4 isolates at 5, 10, 15, 20 or 25 °C on leaves of oilseed rape cultivars Eurol and Darmor lacking the resistance gene Rlm4, which corresponds to AvrLm4. At all temperatures tested, AvrLm4 Ascospores produced more lesions than avrLm4 Ascospores. The diameters of lesions produced by AvrLm4 Ascospores were greater than those of lesions produced by avrLm4 Ascospores. At 15–20 °C, more lesions initiated by AvrLm4 Ascospores produced pycnidia than did lesions initiated by avrLm4 Ascospores. However, there were no differences between AvrLm4 and avrLm4 isolates in incubation period (from inoculation to appearance of lesions) or rate of mycelial growth in leaves from lesions towards the stems. In field experiments with winter oilseed rape cultivars lacking Rlm4, the frequency of AvrLm4 isolates increased from 5.7% at the phoma leaf lesion stage (autumn) to 20.5% at the stem canker stage (summer) during 2002/2003 and from 7.9 to 11.5% during 2003/2004 growing seasons. Results of controlled environment and field experiments indicate that avrLm4 isolates have a fitness cost compared to AvrLm4 isolates.
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effects of temperature on germination and hyphal growth from Ascospores of a group and b group leptosphaeria maculans phoma stem canker of oilseed rape
Annals of Applied Biology, 2001Co-Authors: Yongju Huang, C Toscanounderwood, Bruce D L Fitt, A D Todd, J S West, B Koopmann, Mariehelene BalesdentAbstract:Ascospores of both A-group and B-group Leptosphaeria maculans germinated at temperatures from 5-20degreesC on distilled water agar or detached oilseed rape leaves. After 2 h of incubation on water agar, some A-group Ascospores had germinated at 10-20degreesC and some B-group Ascospores had germinated at 5-20degreesC. The percentages of both A-group and B-group Ascospores that had germinated after 24 h of incubation increased with increasing temperature from 5-20'C. The observed time (Vo(50)) which elapsed from inoculation until 50% of the spores had germinated was shorter for B-group than for A-group Ascospores. Germ tube length increased with increasing temperature from 5-20degreesC for both Ascospore groups. Germ tubes from B-group Ascospores were longer than germ tubes from A-group Ascospores at all temperatures tested, but the mean diameter of germ tubes from A-group Ascospores (1.8 mum) was greater than that of those from B-group Ascospores (1.2 mum) at 15degreesC and 20degreesC. The average number of germ tubes produced from A-group Ascospores (3.8) was greater than that from B-group Ascospores (3.1) after 24 h of incubation at 20degreesC, on both water agar and leaf surfaces. Germ tubes originated predominantly From interstitial cells or terminal cells of A-group or B-group Ascospores, respectively, on both water agar and leaf surfaces. Hyphae from A-group Ascospores grew tortuously with extensive branching, whilst those from B-group Ascospores were predominantly long and straight with little branching, whether the Ascospores were produced from oilseed rape debris or from crosses between single Ascospore isolates, and whether Ascospores were germinating on water agar or leaf surfaces.
Philippe Silar - One of the best experts on this subject based on the ideXlab platform.
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The PaAlr1 magnesium transporter is required for Ascospore development in Podospora anserina.
Fungal biology, 2012Co-Authors: Pierre Grognet, Hervé Lalucque, Philippe SilarAbstract:Abstract The PaAlr1 gene encoding a putative plasma membrane magnesium (Mg) transporter in Podospora anserina was inactivated. The PaAlr1 Δ mutants showed sensitivity to deprivation and excess Mg 2+ and Ca 2+ . They also exhibited an autonomous Ascospore maturation defect. Mutant Ascospores were arrested at an early stage when they contained two nuclei. These data emphasize the role of Mg ions during sexual development in a filamentous fungus.
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the crucial role of the pls1 tetraspanin during Ascospore germination in podospora anserina provides an example of the convergent evolution of morphogenetic processes in fungal plant pathogens and saprobes
Eukaryotic Cell, 2008Co-Authors: Karine Lambou, Philippe Silar, Fabienne Malagnac, Crystel Barbisan, Didier Tharreau, Marchenri LebrunAbstract:Pls1 tetraspanins were shown for some pathogenic fungi to be essential for appressorium-mediated penetration into their host plants. We show here that Podospora anserina, a saprobic fungus lacking appressorium, contains PaPls1, a gene orthologous to known PLS1 genes. Inactivation of PaPls1 demonstrates that this gene is specifically required for the germination of Ascospores in P. anserina. These Ascospores are heavily melanized cells that germinate under inducing conditions through a specific pore. On the contrary, MgPLS1, which fully complements a ΔPaPls1 Ascospore germination defect, has no role in the germination of Magnaporthe grisea nonmelanized Ascospores but is required for the formation of the penetration peg at the pore of its melanized appressorium. P. anserina mutants with mutation of PaNox2, which encodes the NADPH oxidase of the NOX2 family, display the same Ascospore-specific germination defect as the ΔPaPls1 mutant. Both mutant phenotypes are suppressed by the inhibition of melanin biosynthesis, suggesting that they are involved in the same cellular process required for the germination of P. anserina melanized Ascospores. The analysis of the distribution of PLS1 and NOX2 genes in fungal genomes shows that they are either both present or both absent. These results indicate that the germination of P. anserina Ascospores and the formation of the M. grisea appressorium penetration peg use the same molecular machinery that includes Pls1 and Nox2. This machinery is specifically required for the emergence of polarized hyphae from reinforced structures such as appressoria and Ascospores. Its recurrent recruitment during fungal evolution may account for some of the morphogenetic convergence observed in fungi.
Namboori B. Raju - One of the best experts on this subject based on the ideXlab platform.
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Meiotic silencing in the homothallic fungus Gibberella zeae.
Fungal biology, 2011Co-Authors: Hokyoung Son, Namboori B. Raju, Kyunghun Min, Jungkwan Lee, Yin-won LeeAbstract:The homothallic ascomycete fungus Gibberella zeae is an important pathogen on major cereal crops. The objective of this study was to determine whether meiotic silencing occurs in G. zeae. Cytological studies demonstrated that GFP and RFP-fusion proteins were not detected during meiosis, both in heterozygous outcrosses and homozygous selfings. The deletion of rsp-1, a homologue used for studies on meiotic silencing of Neurospora crassa, triggered abnormal Ascospores from selfing, but outcrosses between the mutant and wild-type strain resulted in some Ascospores with mutant phenotype (low occurrence of ascus dominance). When the ectopic mutants that carried an additional copy of rsp-1 were selfed, they primarily produced Ascospores with normal shape but a few Ascospores (0.23 %) were abnormal, in which both endogenous and ectopically integrated genes contained numerous point mutations. The ectopic mutants showed low occurrence of ascus dominance in outcrosses with strains that carried the wild-type allele. Approximately 10 % of Ascospores were abnormal but all of the single-Ascospore isolates produced normal-shaped Ascospores from selfing. However, no ascus dominance was observed when the mutants were outcrossed with a sad-1 deletion mutant, which lacks the putative RNA-dependent RNA polymerase essential for meiotic silencing in N. crassa. All results were consistent with those generated from an additional gene, roa, required for Ascospore morphogenesis. This study demonstrated that G. zeae possesses a functional meiotic silencing mechanism which is triggered by unpaired DNA, as in N. crassa.
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Functional heterothallism resulting from homokaryotic conidia and Ascospores in Neurospora tetrasperma
Fungal Biology, 1992Co-Authors: Namboori B. RajuAbstract:Each Ascospore of Neurospora tetrasperma normally contains haploid nuclei of both mating types, A and a , and produces a self-fertile culture. A majority of cultures from single conidia are also self-fertile, because most conidia are multinucleate and contain nuclei of both mating types. It has long been known that some single-mating type, self-sterile cultures are produced, either from exceptional homokaryotic Ascospores or from the minority of conidia that are homokaryotic. The homokaryotic, self-sterile cultures are crossfertile with strains of opposite mating type, and can be fertilized by compatible nuclei from either homokaryotic or heterokaryotic cultures. The present study shows that the spontaneous proportion of self-sterile propagules from nonmutant strains can be as high as 10% for Ascospores and 20% for conidia. Thus, although N. tetrasperma is predominantly inbred, the species is nevertheless capable of significant heterothallic behaviour and outcrossing. As shown by B. O. Dodge, the Eight-spore mutation E causes most of the asci to produce five to eight Ascospores by affecting spindle behaviour, pairwise association of nuclei, and Ascospore delimitation. Cytological events in crosses heterozygous for E have been re-examined and crosses have also been examined that involve two wild strains which superficially resemble E in producing many homokaryotic Ascospores by a somewhat different mechanism. Events in the developing wild type and mutant asci are documented photographically for the first time.
Yongju Huang - One of the best experts on this subject based on the ideXlab platform.
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fitness cost associated with loss of the avrlm4 avirulence function in leptosphaeria maculans phoma stem canker of oilseed rape
European Journal of Plant Pathology, 2006Co-Authors: Yongju Huang, Bruce D L Fitt, Ziqin Li, N Evans, Thierry Rouxel, Mariehelene BalesdentAbstract:Near-isogenic isolates of Leptosphaeria maculans differing at the AvrLm4 avirulence locus (AvrLm4 or avrLm4) were produced in vitro. Methods for inoculation of leaves of oilseed rape with Ascospores or conidia were compared. The ‘Ascospore shower’ inoculation was the most efficient method for use when inoculum is limited (e.g. Ascospores produced in vitro). It was used in controlled environments to compare fitness of AvrLm4 and avrLm4 isolates at 5, 10, 15, 20 or 25 °C on leaves of oilseed rape cultivars Eurol and Darmor lacking the resistance gene Rlm4, which corresponds to AvrLm4. At all temperatures tested, AvrLm4 Ascospores produced more lesions than avrLm4 Ascospores. The diameters of lesions produced by AvrLm4 Ascospores were greater than those of lesions produced by avrLm4 Ascospores. At 15–20 °C, more lesions initiated by AvrLm4 Ascospores produced pycnidia than did lesions initiated by avrLm4 Ascospores. However, there were no differences between AvrLm4 and avrLm4 isolates in incubation period (from inoculation to appearance of lesions) or rate of mycelial growth in leaves from lesions towards the stems. In field experiments with winter oilseed rape cultivars lacking Rlm4, the frequency of AvrLm4 isolates increased from 5.7% at the phoma leaf lesion stage (autumn) to 20.5% at the stem canker stage (summer) during 2002/2003 and from 7.9 to 11.5% during 2003/2004 growing seasons. Results of controlled environment and field experiments indicate that avrLm4 isolates have a fitness cost compared to AvrLm4 isolates.
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effects of temperature on germination and hyphal growth from Ascospores of a group and b group leptosphaeria maculans phoma stem canker of oilseed rape
Annals of Applied Biology, 2001Co-Authors: Yongju Huang, C Toscanounderwood, Bruce D L Fitt, A D Todd, J S West, B Koopmann, Mariehelene BalesdentAbstract:Ascospores of both A-group and B-group Leptosphaeria maculans germinated at temperatures from 5-20degreesC on distilled water agar or detached oilseed rape leaves. After 2 h of incubation on water agar, some A-group Ascospores had germinated at 10-20degreesC and some B-group Ascospores had germinated at 5-20degreesC. The percentages of both A-group and B-group Ascospores that had germinated after 24 h of incubation increased with increasing temperature from 5-20'C. The observed time (Vo(50)) which elapsed from inoculation until 50% of the spores had germinated was shorter for B-group than for A-group Ascospores. Germ tube length increased with increasing temperature from 5-20degreesC for both Ascospore groups. Germ tubes from B-group Ascospores were longer than germ tubes from A-group Ascospores at all temperatures tested, but the mean diameter of germ tubes from A-group Ascospores (1.8 mum) was greater than that of those from B-group Ascospores (1.2 mum) at 15degreesC and 20degreesC. The average number of germ tubes produced from A-group Ascospores (3.8) was greater than that from B-group Ascospores (3.1) after 24 h of incubation at 20degreesC, on both water agar and leaf surfaces. Germ tubes originated predominantly From interstitial cells or terminal cells of A-group or B-group Ascospores, respectively, on both water agar and leaf surfaces. Hyphae from A-group Ascospores grew tortuously with extensive branching, whilst those from B-group Ascospores were predominantly long and straight with little branching, whether the Ascospores were produced from oilseed rape debris or from crosses between single Ascospore isolates, and whether Ascospores were germinating on water agar or leaf surfaces.
P. Halama - One of the best experts on this subject based on the ideXlab platform.
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tetrad analysis of mating type mutations esterase and aggressiveness in phaeosphaeria nodorum
Fungal Biology, 1999Co-Authors: P. Halama, M. Skajennikoff, B DehorterAbstract:Ascospore progenies from two crosses between a wild single-Ascospore strain and two mutants of Phaeosphaeria nodorum were obtained in vitro. Cultural characters, sensitivity to carbendazim (MBC), nitrate utilization, mating type, esterase zymograms and aggressiveness of these progenies and parents were compared and differences were detected between the Ascospores. The single-Ascospore strains from each single ascus could always be grouped into four pairs using a combination of markers. Recombinations were observed between nitrate non-utilizing phenotype and mating type or esterase patterns for one cross. For the other cross, recombinations between MBC resistance and esterase patterns were detected. The values of aggressiveness in each progeny were distributed along a wide range confirming the polygenic character of aggressiveness in P. nodorum. No close relationship was observed between in vitro conidiogenesis, the intensity of leaf necrosis and the fertile pycnidia production on leaf lesions.
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La reproduction sexuée et l'agressivité de Phaeosphaeria nodorum Hedj (= Septoria nodorum Berk)
EDP Sciences, 1992Co-Authors: F. Rapilly, P. Halama, M. Skajennikoff, G. TouraudAbstract:La variabilité de l'agressivité, de Septoria nodorum, parasite du blé, a été l'objet de nombreuses études. Cet article présente la variabilité obtenue, chez ce parasite, après reproduction sexuée. Les 8 souches monoAscospores provenant d'un même asque de Phaeosphaeria nodorum sont comparées, sur diverses variétés de blé, par l'appréciation sur feuilles détachées de la progression des nécroses foliaires et par la mesure de la quantité d'éthylène produite après contamination. Ce champignon est hétérothallique; la comparaison des 2 groupes d'incompatibilité sexuelle montre que ceux-ci sont en moyenne d'agressivité comparable; au sein de chaque groupe, les amplitudes obtenues entre les Ascospores sont de même grandeur. Les 4 paires d'Ascospores jumelles reconnues sur la base des caractères culturaux ne sont pas identifiables sur la base des critères utilisés pour les feuilles en survie ou sur la base de la progression des épidémies. Par le pouvoir pathogène, la reconnaissance des Ascospores jumelles se révèle impossible. La descendance conidienne d'une même Ascospore est hétérogène. Des hypothèses sont formulées pour expliquer, d'une part, la non-reconnaissance des jumeaux, et d'autre part, l'hétérogénéité de la descendance d'une Ascospore.Sexual reproduction and aggressiveness of Phaeosphaeria nodorum Hedj (= Septoria nodorum Berk). The variability in aggressiveness of Septoria nodorum, a wheat pathogen, has been extensively studied. This article presents the variability obtained in this pathogen after sexual reproduction. The 8 mono-ascosporous strains originating from the same Phaeosphaeria nodorum ascus were compared by assessing the progression of leaf necroses on detached leaves of various wheat varieties and by measuring the quantity of ethylene produced after contamination. This fungus is heterothallic; the comparison between the 2 sexually incompatible groups showed that on average they are similarly aggressive. In each group the ranges obtained between Ascospores were of the same size. The 4 pairs of twin Ascospores identified on the basis of cultural characteristics were not identifiable on the basis of criteria used for detached leaves, or of the progression of epidemics. For pathogenicity, identification of twin Ascospores was impossible. Conidian progeny of the same Ascospore was shown to be heterogeneous. Hypotheses have been proposed to explain the non-identification of twins and, also, the heterogeneity of the Ascospore progeny
