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Petit-Houdenot Y, Degrave A, Meyer M, Blaise F, Ollivier B, Marais CL, Jauneau A, Audran C, Rivas S, Veneault-Fourrey C, Brun H, Rouxel T, Fudal I, Balesdent MH. A two genes - for - one gene interaction between Leptosphaeria maculans and Brassica napus. THE NEW PHYTOLOGIST 2019; 223:397-411. [PMID: 30802965 DOI: 10.1111/nph.15762] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2019] [Accepted: 02/18/2019] [Indexed: 05/26/2023]
Abstract
Interactions between Leptosphaeria maculans, causal agent of stem canker of oilseed rape, and its Brassica hosts are models of choice to explore the multiplicity of 'gene-for-gene' complementarities and how they diversified to increased complexity in the course of plant-pathogen co-evolution. Here, we support this postulate by investigating the AvrLm10 avirulence that induces a resistance response when recognized by the Brassica nigra resistance gene Rlm10. Using genome-assisted map-based cloning, we identified and cloned two AvrLm10 candidates as two genes in opposite transcriptional orientation located in a subtelomeric repeat-rich region of the genome. The AvrLm10 genes encode small secreted proteins and show expression profiles in planta similar to those of all L. maculans avirulence genes identified so far. Complementation and silencing assays indicated that both genes are necessary to trigger Rlm10 resistance. Three assays for protein-protein interactions showed that the two AvrLm10 proteins interact physically in vitro and in planta. Some avirulence genes are recognized by two distinct resistance genes and some avirulence genes hide the recognition specificities of another. Our L. maculans model illustrates an additional case where two genes located in opposite transcriptional orientation are necessary to induce resistance. Interestingly, orthologues exist for both L. maculans genes in other phytopathogenic species, with a similar genome organization, which may point to an important conserved effector function linked to heterodimerization of the two proteins.
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Affiliation(s)
- Yohann Petit-Houdenot
- UMR BIOGER, INRA, AgroParisTech, Université Paris-Saclay, Avenue Lucien Brétignières, BP 01, Thiverval-Grignon, F-78850, France
| | - Alexandre Degrave
- UMR BIOGER, INRA, AgroParisTech, Université Paris-Saclay, Avenue Lucien Brétignières, BP 01, Thiverval-Grignon, F-78850, France
| | - Michel Meyer
- UMR BIOGER, INRA, AgroParisTech, Université Paris-Saclay, Avenue Lucien Brétignières, BP 01, Thiverval-Grignon, F-78850, France
| | - Françoise Blaise
- UMR BIOGER, INRA, AgroParisTech, Université Paris-Saclay, Avenue Lucien Brétignières, BP 01, Thiverval-Grignon, F-78850, France
| | - Bénédicte Ollivier
- UMR BIOGER, INRA, AgroParisTech, Université Paris-Saclay, Avenue Lucien Brétignières, BP 01, Thiverval-Grignon, F-78850, France
| | - Claire-Line Marais
- UMR BIOGER, INRA, AgroParisTech, Université Paris-Saclay, Avenue Lucien Brétignières, BP 01, Thiverval-Grignon, F-78850, France
| | - Alain Jauneau
- Plateforme Imagerie, Pôle de Biotechnologie Végétale, Fédération de Recherche 3450, Castanet-Tolosan, F-31326, France
| | - Corinne Audran
- LIPM, Université de Toulouse, INRA, CNRS, Castanet-Tolosan, F-31326, France
| | - Susana Rivas
- LIPM, Université de Toulouse, INRA, CNRS, Castanet-Tolosan, F-31326, France
| | - Claire Veneault-Fourrey
- Laboratoire d'Excellence ARBRE, Centre INRA-Lorraine, INRA, UMR 1136, INRA-Université de Lorraine Interactions Arbres/Microorganismes, Champenoux, F-54280, France
- Laboratoire d'Excellence ARBRE, Faculté des Sciences et Technologies, UMR 1136 INRA-Université de Lorraine Interactions Arbres/Microorganismes, Université de Lorraine, Vandoeuvre les Nancy, F-54506, France
| | | | - Thierry Rouxel
- UMR BIOGER, INRA, AgroParisTech, Université Paris-Saclay, Avenue Lucien Brétignières, BP 01, Thiverval-Grignon, F-78850, France
| | - Isabelle Fudal
- UMR BIOGER, INRA, AgroParisTech, Université Paris-Saclay, Avenue Lucien Brétignières, BP 01, Thiverval-Grignon, F-78850, France
| | - Marie-Hélène Balesdent
- UMR BIOGER, INRA, AgroParisTech, Université Paris-Saclay, Avenue Lucien Brétignières, BP 01, Thiverval-Grignon, F-78850, France
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Zhang YJ, Hou JX, Zhang S, Hausner G, Liu XZ, Li WJ. The intronic minisatellite OsMin1 within a serine protease gene in the Chinese caterpillar fungus Ophiocordyceps sinensis. Appl Microbiol Biotechnol 2016; 100:3599-610. [PMID: 26754819 DOI: 10.1007/s00253-016-7287-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2015] [Revised: 12/24/2015] [Accepted: 12/29/2015] [Indexed: 12/01/2022]
Abstract
Repetitive DNA sequences make up a significant portion of all genomes and may occur in intergenic, regulatory, coding, or even intronic regions. Partial sequences of a serine protease gene csp1 was previously used as a population genetic marker of the Chinese caterpillar fungus Ophiocordyceps sinensis, but its first intron region was excluded due to ambiguous alignment. Here in this study, we report the presence of a minisatellite OsMin1 within this intron, where a 20(19)-bp repeat motif is duplicated two to six times in different isolates. Fourteen intron alleles and 13 OsMin1 alleles were identified among 125 O. sinensis samples distributed broadly on the Tibetan Plateau. Two OsMin1 alleles were prevalent, corresponding to either two or five repeats of the core sequence motif. OsMin1 appears to be a single locus marker in the O. sinensis genome, but its origin is undetermined. Abundant recombination signals were detected between upstream and downstream flanking regions of OsMin1, suggesting that OsMin1 mutate by unequal crossing over. Geographic distribution, fungal phylogeny, and host insect phylogeny all significantly affected intron distribution patterns but with the greatest influence noted for fungal genotypes and the least for geography. As far as we know, OsMin1 is the first minisatellite found in O. sinensis and the second found in fungal introns. OsMin1 may be useful in designing an efficient protocol to discriminate authentic O. sinensis from counterfeits.
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Affiliation(s)
- Yong-Jie Zhang
- School of Life Sciences, Shanxi University, Taiyuan, 030006, China.
| | - Jun-Xiu Hou
- School of Life Sciences, Shanxi University, Taiyuan, 030006, China
| | - Shu Zhang
- Institute of Applied Chemistry, Shanxi University, Taiyuan, 030006, China
| | - Georg Hausner
- Department of Microbiology, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada
| | - Xing-Zhong Liu
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, 100101, China.
| | - Wen-Jia Li
- Sunshine Lake Pharma Co., LTD, Dongguan, 523808, China
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Vincenot L, Balesdent MH, Li H, Barbetti MJ, Sivasithamparam K, Gout L, Rouxel T. Occurrence of a new subclade of Leptosphaeria biglobosa in Western Australia. PHYTOPATHOLOGY 2008; 98:321-329. [PMID: 18944083 DOI: 10.1094/phyto-98-3-0321] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Stem canker of crucifers is caused by an ascomycete species complex comprising of two main species, Leptosphaeria maculans and L. biglobosa. These are composed of at least seven distinct subclades based on biochemical data or on sequences of internal transcribed spacer (ITS), the mating type MAT1-2 or fragments of actin or beta-tubulin genes. In the course of a wide-scale characterization of the race structure of L. maculans from Western Australia, a few isolates from two locations failed to amplify specific sequences of L. maculans, i.e., the mating-type or minisatellite alleles. Based on both pathogenicity tests and ITS size, these isolates were classified as belonging to the L. biglobosa species. Parsimony and distance analyses performed on ITS, actin and beta-tubulin sequences revealed that these isolates formed a new L. biglobosa subclade, more related to the Canadian L. biglobosa 'canadensis' subclade than to the L. biglobosa 'australensis' isolates previously described in Australia (Victoria). They are termed here as L. biglobosa 'occiaustralensis'. These isolates were mainly recovered from resistant oilseed rape cultivars that included the Brassica rapa sp. sylvestris-derived resistance source, but not from the susceptible cv. Westar. The pathogenicity of L. biglobosa 'occiaustralensis' to cotyledons of most oilseed rape genotypes was higher than that of L. biglobosa 'canadensis' or L. biglobosa 'australensis' isolates.
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Affiliation(s)
- L Vincenot
- INRA, UMR 1290 (BIOGER-CPP), Route de Saint Cyr, 78026 Versailles Cedex, France
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Gout L, Kuhn ML, Vincenot L, Bernard-Samain S, Cattolico L, Barbetti M, Moreno-Rico O, Balesdent MH, Rouxel T. Genome structure impacts molecular evolution at the AvrLm1 avirulence locus of the plant pathogen Leptosphaeria maculans. Environ Microbiol 2007; 9:2978-92. [DOI: 10.1111/j.1462-2920.2007.01408.x] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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Hayden HL, Cozijnsen AJ, Howlett BJ. Microsatellite and Minisatellite Analysis of Leptosphaeria maculans in Australia Reveals Regional Genetic Differentiation. PHYTOPATHOLOGY 2007; 97:879-87. [PMID: 18943938 DOI: 10.1094/phyto-97-7-0879] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
ABSTRACT The population genetic structure of the fungal pathogen Leptosphaeria maculans was determined in Australia using six microsatellite and two minisatellite markers. Ascospores were sampled from Brassica napus stubble in disease nurseries and commercial fields in different sites over 2 years. The 13 subpopulations of L. maculans exhibited high gene (H = 0.393 to 0.563) and genotypic diversity, with 357 haplotypes identified among 513 isolates. Although the majority of genetic variation was distributed within subpopulations (85%), 10% occurred between the regions of eastern and Western Australia, and 5% within regions. F(ST) analysis of subpopulation pairs also showed the east-west genetic differentiation, whereas factorial correspondence analysis separated Western Australian subpopulations from eastern ones. Bayesian model-based population structure analyses of multilocus haplotypes inferred three distinct populations, one in Western Australia and an admixture of two in eastern Australia. These two regions are separated by 1,200 km of arid desert that may act as a natural barrier to gene flow, resulting in differentiation by random genetic drift. The genetic differentiation of L. maculans isolates between eastern and Western Australia means that these regions can be treated as different management units, and reinforces the need for widespread disease nurseries in each region to screen breeding lines against a range of genetic and pathogenic populations of L. maculans.
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Gout L, Eckert M, Rouxel T, Balesdent MH. Genetic variability and distribution of mating type alleles in field populations of Leptosphaeria maculans from France. Appl Environ Microbiol 2006; 72:185-91. [PMID: 16391041 PMCID: PMC1352181 DOI: 10.1128/aem.72.1.185-191.2006] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2005] [Accepted: 10/03/2005] [Indexed: 11/20/2022] Open
Abstract
Leptosphaeria maculans is the most ubiquitous fungal pathogen of Brassica crops and causes the devastating stem canker disease of oilseed rape worldwide. We used minisatellite markers to determine the genetic structure of L. maculans in four field populations from France. Isolates were collected at three different spatial scales (leaf, 2-m2 field plot, and field) enabling the evaluation of spatial distribution of the mating type alleles and of genetic variability within and among field populations. Within each field population, no gametic disequilibrium between the minisatellite loci was detected and the mating type alleles were present at equal frequencies. Both sexual and asexual reproduction occur in the field, but the genetic structure of these populations is consistent with annual cycles of randomly mating sexual reproduction. All L. maculans field populations had a high level of gene diversity (H = 0.68 to 0.75) and genotypic diversity. Within each field population, the number of genotypes often was very close to the number of isolates. Analysis of molecular variance indicated that >99.5% of the total genetic variability was distributed at a small spatial scale, i.e., within 2-m2 field plots. Population differentiation among the four field populations was low (GST < 0.02), suggesting a high degree of gene exchange between these populations. The high gene flow evidenced here in French populations of L. maculans suggests a rapid countrywide diffusion of novel virulence alleles whenever novel resistance sources are used.
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Affiliation(s)
- Lilian Gout
- Phytopathologie et Méthodologies de la Détection, INRA, Unité PMDV, Route de Saint Cyr, 78026 Versailles Cedex, France
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Balesdent MH, Barbetti MJ, Li H, Sivasithamparam K, Gout L, Rouxel T. Analysis of Leptosphaeria maculans Race Structure in a Worldwide Collection of Isolates. PHYTOPATHOLOGY 2005; 95:1061-1071. [PMID: 18943304 DOI: 10.1094/phyto-95-1061] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
ABSTRACT Leptosphaeria maculans, the causal agent of stem canker of oilseed rape, develops gene-for-gene interactions with its hosts. To date, eight L. maculans avirulence (Avr) genes, AvrLm1 to AvrLm8, have been genetically characterized. An additional Avr gene, AvrLm9, that interacts with the resistance gene Rlm9, was genetically characterized here following in vitro crosses of the pathogen. A worldwide collection of 63 isolates, including the International Blackleg of Crucifers Network collection, was genotyped at these nine Avr loci. In a first step, isolates were classified into pathogenicity groups (PGs) using two published differential sets. This analysis revealed geographical disparities as regards the proportion of each PG. Genotyping of isolates at all Avr loci confirmed the disparities between continents, in terms of Avr allele frequencies, particularly for AvrLm2, AvrLm3, AvrLm7, AvrLm8, and AvrLm9, or in terms of race structure, diversity, and complexity. Twenty-six distinct races were identified in the collection. A larger number of races (n = 18) was found in Australia than in Europe (n = 8). Mean number of virulence alleles per isolate was also higher in Australia (5.11 virulence alleles) than in Europe (4.33) and Canada (3.46). Due to the diversity of populations of L. maculans evidenced here at the race level, a new, open terminology is proposed for L. maculans race designation, indicating all Avr loci for which the isolate is avirulent.
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Hayden HL, Howlett BJ. Genetic structure of a population of the fungus Leptosphaeria maculans in a disease nursery of Brassica napus in Australia. Curr Genet 2005; 48:142-9. [PMID: 16032414 DOI: 10.1007/s00294-005-0006-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2005] [Revised: 06/10/2005] [Accepted: 06/12/2005] [Indexed: 10/25/2022]
Abstract
Microsatellite, minisatellite and mating type markers were used to determine the genetic structure of the fungus Leptosphaeria maculans within a disease nursery, where Brassica napus lines were screened for resistance to blackleg disease under high inoculum pressure. Fungal isolates were collected from pseudothecia in infected stubble and pycnidia within cotyledon lesions on seedlings within the nursery. Genetic diversity was high with gene diversity at H=0.700 across four polymorphic loci, and genotypic diversity at D=0.993. Among the 159 isolates analysed, 102 multilocus genotypes were identified. The even distribution of mating type idiomorphs MAT1-1 and MAT1-2 and gametic equilibrium within the population provided further evidence of random mating. Genetic diversity was distributed on a very fine scale in the disease nursery. The majority of genetic diversity (67%) was distributed among conidia within a lesion or among ascospores from a piece of stubble, while the remainder (33%) was distributed within lesions on seedlings or different stubble pieces. There were no among-group differences between samples from stubble and seedlings. This is consistent with the low level of genetic differentiation between the ascospore and conidia samples (F (ST)=0.017) indicating that all isolates of L. maculans from the disease nursery most likely belong to one population, and that ascospores form the primary inoculum in the disease nursery.
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Affiliation(s)
- Helen L Hayden
- School of Botany, The University of Melbourne, Melbourne, VIC 3010, Australia.
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Rouxel T, Balesdent MH. The stem canker (blackleg) fungus, Leptosphaeria maculans, enters the genomic era. MOLECULAR PLANT PATHOLOGY 2005; 6:225-41. [PMID: 20565653 DOI: 10.1111/j.1364-3703.2005.00282.x] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
UNLABELLED SUMMARY Leptosphaeria maculans is the most ubiquitous pathogen of Brassica crops, and mainly oilseed brassicas (oilseed rape, canola), causing the devastating 'stem canker' or 'blackleg'. This review summarizes our current knowledge on the pathogen, from taxonomic issues to specific life traits. It mainly illustrates the importance of formal genetics approaches on the pathogen side to dissect the interaction with the host plants. In addition, this review presents the main current research topics on L. maculans and focuses on the L. maculans genome initiative recently begun, including its main research issues. TAXONOMY Leptosphaeria maculans (Desm.) Ces. & de Not. (anamorph Phoma lingam Tode ex Fr.). Kingdom Fungi, Phylum Ascomycota, Class Dothideomycetes (Loculoascomycetes), Order Pleosporales, Genus Leptosphaeria, Species maculans. HOST RANGE cultivated Brassicas such as Brassica napus (oilseed rape, canola), B. rapa, B. juncea, B. oleracea, etc., along with numerous wild crucifers species. Arabidopsis thaliana was recently reported to be a potential host for L. maculans. Primary disease symptoms are greyish-green collapse of cotyledon or leaf tissue, without a visible margin, bearing tiny black spots (pycnidia). The fungus then develops an endophytic symptomless growth for many months. Secondary symptoms, at the end of the growing season, are dry necroses of the crown tissues with occasional blackening (stem canker or blackleg) causing lodging of the plants. Pseudothecia differentiate on leftover residues. Seedling damping-off and premature ripening are also reported under certain environmental conditions. USEFUL WEBSITES Leptosphaeria maculans sequencing project at Genoscope: http://www.genoscope.cns.fr/externe/English/Projets/Projet_DM/organisme_DM.html; the SECURE site: http://www.secure.rothamsted.ac.uk/ the 'Blackleg' group at the University of Melbourne: http://www.botany.unimelb.edu.au/blackleg/overview.htm.
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Affiliation(s)
- T Rouxel
- INRA-PMDV, Route de Saint Cyr, 78026 Versailles Cedex, France
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Eckert M, Gout L, Rouxel T, Blaise F, Jedryczka M, Fitt B, Balesdent MH. Identification and characterization of polymorphic minisatellites in the phytopathogenic ascomycete Leptosphaeria maculans. Curr Genet 2004; 47:37-48. [PMID: 15614492 DOI: 10.1007/s00294-004-0539-z] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2004] [Revised: 09/14/2004] [Accepted: 09/28/2004] [Indexed: 10/26/2022]
Abstract
Leptosphaeria maculans causes phoma stem canker, the most serious disease of oilseed rape world-wide. Sexual recombination is important in the pathogen life cycle and increases the risk of plant resistance genes being overcome rapidly. Thus, there is a need to develop easy-to-use molecular markers suitable for large-scale population genetic studies. The minisatellite MinLm1, showing six alleles in natural populations, has previously been used as a marker to survey populations. Here, we report the characterization of five new minisatellites (MinLm2-MinLm6), of which four were identified by a systematic search for tandemly repeated polymorphic regions in BAC-end sequencing data from L. maculans. Of 782 BAC-end sequences analysed, 43 possessed putative minisatellite-type repeats and four of these (MinLm3-MinLm6) displayed both consistent PCR amplification and size polymorphism in a collection of L. maculans isolates of diverse origins. Cloning and sequencing of each allele confirmed that polymorphism was due to variation in the repeat number of a core motif ranging from 11 bp (MinLm3) to 51 bp (MinLm4). The number of alleles found for each minisatellite ranged from three (MinLm4) to nine (MinLm2), with eight, five and six for MinLm3, MinLm5 and MinLm6, respectively. MinLm2-MinLm6 are all single locus markers specific to L. maculans and share some common features, such as conservation of core motifs and incomplete direct repeats in the flanking regions. To our knowledge, L. maculans is the first fungal species for which six polymorphic single locus minisatellite markers have been reported.
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Mendes-Pereira E, Balesdent MH, Brun H, Rouxel T. Molecular phylogeny of the Leptosphaeria maculans-L. biglobosa species complex. ACTA ACUST UNITED AC 2004; 107:1287-304. [PMID: 15000231 DOI: 10.1017/s0953756203008554] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Leptosphaeria maculans (anamorph Phoma lingam), the ascomycete causing stem canker of crucifers, is a species complex that can be separated into at least seven distinct subgroups using a combination of biochemical and molecular criteria. In the present study sequences of the entire ITS region, including the 5.8S rDNA, of 38 isolates representing the seven subgroups, along with specimens from culture collections, were analysed, compared to those of closely related Leptosphaperia species, and the phylogeny inferred using parsimony and distance analyses. A well-supported clade encompassed all isolates of the seven subgroups along with L. conferta, a known saprobe of dried crucifer stems. The L. maculans isolates were further separated into two well-supported clades corresponding to L. maculans s. str. and the recently named L. biglobosa. Parsimony and distance analyses further separated groups within both species, usually corresponding to specific host plants or geographic origin, e.g. L. maculans 'brassicae' from cultivated Brassica, L. maculans 'lepidii'. from Lepidium sp., L. biglobosa 'brassicae', from various Brassica species, L. biglobosa 'thlaspii' from Thlaspi arvense, L. biglobosa 'erysimii' from Erysimum sp., and L. biglobosa 'canadensis' mostly found in central Canada. The oldest L. maculans specimens maintained in international collections clustered with either L. maculans 'brassicae', L. biglobosa 'brassicae', or a still different group closely related to L. biglobosa 'thlaspii'. The evolutionary relationships between the seven infraspecific groups are discussed in terms of phytopathological relevance and species isolation linked with specific life cycle, geographic isolation or host specificity.
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Affiliation(s)
- Edouard Mendes-Pereira
- Unité Phytopathologie et Méthodologies de la Détection Versailles, Institut National de la Recherche Agronomique, Route de Saint Cyr, F-78026 Versailles, France
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Balesdent MH, Attard A, Kühn ML, Rouxel T. New Avirulence Genes in the Phytopathogenic Fungus Leptosphaeria maculans. PHYTOPATHOLOGY 2002; 92:1122-33. [PMID: 18944223 DOI: 10.1094/phyto.2002.92.10.1122] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
ABSTRACT Leptosphaeria maculans, the causal agent of stem canker of oilseed rape (Brassica napus), develops gene-for-gene interactions with oilseed rape, and four L. maculans avirulence (AVR) genes (AvrLm1, AvrLm2, AvrLm4, and alm1) were previously genetically characterized. Based on the analysis of progeny of numerous in vitro crosses between L. maculans isolates showing either already characterized or new differential interactions, this work aims to provide an overview of the AVR genes that may specify incompatibility toward B. napus and the related species B. juncea and B. rapa. Two novel differential interactions were thus identified between L. maculans and B. napus genotypes, one of them corresponding to a complete resistance to European races of L. maculans. In both cases, a single gene control of avirulence was established (genes AvrLm3 and AvrLm7). Similarly, a single gene control of avirulence toward a B. rapa genotype, also resistant to European L. maculans isolates, was demonstrated (gene AvrLm8). Finally, a digenic control of avirulence toward B. juncea was established (genes AvrLm5 and AvrLm6). Linkage analyses demonstrated that at least four unlinked L. maculans genomic regions, including at least one AVR gene cluster (AvrLm1-AvrLm2-AvrLm6), are involved in host specificity. The AvrLm3-AvrLm4-AvrLm7 region may correspond either to a second AVR gene cluster or to a multiallelic AVR gene.
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Attard A, Gout L, Gourgues M, Kühn ML, Schmit J, Laroche S, Ansan-Melayah D, Billault A, Cattolico L, Balesdent MH, Rouxel T. Analysis of molecular markers genetically linked to the Leptosphaeria maculans avirulence gene AvrLm1 in field populations indicates a highly conserved event leading to virulence on Rlm1 genotypes. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2002; 15:672-682. [PMID: 12118883 DOI: 10.1094/mpmi.2002.15.7.672] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Map-based cloning of the avirulence gene AvrLm1 of Leptosphaeria maculans was initiated utilizing a genetic map of the fungus and a BAC library constructed from an AvrLm1 isolate. Seven polymorphic DNA markers closely linked to AvrLm1 were identified. Of these, two were shown to border the locus on its 5' end and were present, with size polymorphism, in both the virulent and the avirulent isolates. In contrast, three markers, J19-1.1, J53-1.3 (in coupling phase with avirulence), and Vir1 (in repulsion phase with avirulence), cosegregated with AvrLm1 in 312 progeny from five in vitro crosses. J19-1.1 and J53-1.3 were never amplified in the virulent parents or progeny, whereas Vir1 was never amplified in the avirulent parents or progeny. J19-1.1 and J53-1.3 were shown to be separated by 40 kb within a 184-kb BAC contig. In addition, the 1.6-cM genetic distance between J53-1.3 and the nearest recombinant marker corresponded to a 121-kb physical distance. When analyzing a European Union-wide collection of 192 isolates, J53-1.3, J19-1.1, and Vir1 were found to be closely associated with the AvrLm1 locus. The results of polymerase chain reaction amplification with primers for the three markers were in accordance with the interaction phenotype for 92.2% (J53-1.3), 90.6% (J19-1.1), and 88.0% (Vir1) of the isolates. In addition, genome organization of the AvrLm1 region was highly conserved in field isolates, because 89.1% of the avirulent isolates and 79.0% of the virulent isolates showed the same association of markers as that of the parents of in vitro crosses. The large-scale analysis of field isolates with markers originating from the genetic map therefore confirms (i) the physical proximity between the markers and the target locus and (ii) that AvrLm1 is located in (or close to) a recombination-deficient genome region. As a consequence, map-based markers provided us with high-quality markers for an overview of the occurrence of race "AvrLm1" at the field scale. These data were used to propose hypotheses on evolution towards virulence in field isolates.
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Affiliation(s)
- Agnès Attard
- Institute National de la Recherche Agronomique, Pathologie Végétale, Versailles, France
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