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Lu F, Ren Y, Ding L, Lu J, Zhou X, Liu H, Wang N, Cai M. Minos and Restless transposon insertion mutagenesis of psychrotrophic fungus for red pigment synthesis adaptive to normal temperature. BIORESOUR BIOPROCESS 2022; 9:118. [PMID: 38647871 PMCID: PMC10992017 DOI: 10.1186/s40643-022-00604-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2022] [Accepted: 10/17/2022] [Indexed: 11/06/2022] Open
Abstract
The polar psychrotrophic fungus Geomyces sp. WNF-15A can produce high-quality natural red pigment for the potential use as edible pigment. However, it shows low-temperature-dependent synthesis of red pigment, which limits its large-scale industrial applications due to the difficult and high-cost bioprocess control. This study aims to develop transposon-mediated mutagenesis methods to generate mutants that are able to synthesize red pigment at normal temperature. Four transposable systems, including single and dual transposable systems, were established in this fungus based on the Minos from Drosophila hydei and the Restless from Tolypocladium inflatum. A total of 23 production-dominant mutants and 12 growth-dominant mutants were thus obtained by constructed transposable systems. At 14 °C and 20 °C, the MPS1 mutant strain achieved the highest level of red pigment (OD520 of 43.3 and 29.7, respectively), which was increased by 78.4% and 128.7% compared to the wild-type, respectively. Of note, 4 mutants (MPS1, MPS3, MPS4 and MPD1) successfully synthesized red pigment (OD520 of 5.0, 5.3, 4.7 and 4.9, respectively) at 25 °C, which broke the limit of the wild-type production under normal temperature. Generally, the dual transposable systems of Minos and Restless were more efficient than their single transposable systems for mutagenesis in this fungus. However, the positive mutation ratios were similar between the dual and single transposable systems for either Minos or Restless. This study provides alternative tools for genetic mutagenesis breeding of fungi from extreme environments.
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Affiliation(s)
- Fengning Lu
- State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, 200237, China
| | - Yanna Ren
- State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, 200237, China
| | - Lulu Ding
- State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, 200237, China
| | - Jian Lu
- State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, 200237, China
| | - Xiangshan Zhou
- China Resources Biopharmaceutical Co., Ltd, Unit 601, Building No. 2, YESUN Intelligent Community III, Guanlan Street, Shenzhen, China
| | - Haifeng Liu
- China Resources Angde Biotech Pharma Co., Ltd, 78 E-Jiao Street, Liaocheng, 252201, Shandong, China
| | - Nengfei Wang
- First Institute of Oceanography, Ministry of Natural Resources, Qingdao, 266061, China
| | - Menghao Cai
- State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, Shanghai, 200237, China.
- Shanghai Frontiers Science Center of Optogenetic Techniques for Cell Metabolism, East China University of Science and Technology, 130 Meilong Road, Shanghai, 200237, China.
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Dupeyron M, Baril T, Bass C, Hayward A. Phylogenetic analysis of the Tc1/mariner superfamily reveals the unexplored diversity of pogo-like elements. Mob DNA 2020; 11:21. [PMID: 32612713 PMCID: PMC7325037 DOI: 10.1186/s13100-020-00212-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2019] [Accepted: 04/08/2020] [Indexed: 01/18/2023] Open
Abstract
Background Tc1/mariner transposons are widespread DNA transposable elements (TEs) that have made important contributions to the evolution of host genomic complexity in metazoans. However, the evolution and diversity of the Tc1/mariner superfamily remains poorly understood. Following recent developments in genome sequencing and the availability of a wealth of new genomes, Tc1/mariner TEs have been identified in many new taxa across the eukaryotic tree of life. To date, the majority of studies focussing on Tc1/mariner elements have considered only a single host lineage or just a small number of host lineages. Thus, much remains to be learnt about the evolution of Tc1/mariner TEs by performing analyses that consider elements that originate from across host diversity. Results We mined the non-redundant database of NCBI using BLASTp searches, with transposase sequences from a diverse set of reference Tc1/mariner elements as queries. A total of 5158 Tc1/mariner elements were retrieved and used to reconstruct evolutionary relationships within the superfamily. The resulting phylogeny is well resolved and includes several new groups of Tc1/mariner elements. In particular, we identify a new family of plant-genome restricted Tc1/mariner elements, which we call PlantMar. We also show that the pogo family is much larger and more diverse than previously appreciated, and we review evidence for a potential revision of its status to become a separate superfamily. Conclusions Our study provides an overview of Tc1-mariner phylogeny and summarises the impressive diversity of Tc1-mariner TEs among sequenced eukaryotes. Tc1/mariner TEs are successful in a wide range of eukaryotes, especially unikonts (the taxonomic supergroup containing Amoebozoa, Opisthokonta, Breviatea, and Apusomonadida). In particular, ecdysozoa, and especially arthropods, emerge as important hosts for Tc1/mariner elements (except the PlantMar family). Meanwhile, the pogo family, which is by far the largest Tc1/mariner family, also includes many elements from fungal and chordate genomes. Moreover, there is evidence of the repeated exaptation of pogo elements in vertebrates, including humans, in addition to the well-known example of CENP-B. Collectively, our findings provide a considerable advancement in understanding of Tc1/mariner elements, and more generally they suggest that much work remains to improve understanding of the diversity and evolution of DNA TEs.
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Affiliation(s)
- Mathilde Dupeyron
- Centre for Ecology and Conservation, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE UK
| | - Tobias Baril
- Centre for Ecology and Conservation, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE UK
| | - Chris Bass
- Centre for Ecology and Conservation, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE UK
| | - Alexander Hayward
- Centre for Ecology and Conservation, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE UK
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Evangelinos M, Anagnostopoulos G, Karvela-Kalogeraki I, Stathopoulou PM, Scazzocchio C, Diallinas G. Minos as a novel Tc1/mariner-type transposable element for functional genomic analysis in Aspergillus nidulans. Fungal Genet Biol 2015; 81:1-11. [PMID: 26021704 DOI: 10.1016/j.fgb.2015.05.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Revised: 05/15/2015] [Accepted: 05/18/2015] [Indexed: 10/23/2022]
Abstract
Transposons constitute powerful genetic tools for gene inactivation, exon or promoter trapping and genome analyses. The Minos element from Drosophila hydei, a Tc1/mariner-like transposon, has proved as a very efficient tool for heterologous transposition in several metazoa. In filamentous fungi, only a handful of fungal-specific transposable elements have been exploited as genetic tools, with the impala Tc1/mariner element from Fusarium oxysporum being the most successful. Here, we developed a two-component transposition system to manipulate Minos transposition in Aspergillus nidulans (AnMinos). Our system allows direct selection of transposition events based on re-activation of niaD, a gene necessary for growth on nitrate as a nitrogen source. On average, among 10(8) conidiospores, we obtain up to ∼0.8×10(2) transposition events leading to the expected revertant phenotype (niaD(+)), while ∼16% of excision events lead to AnMinos loss. Characterized excision footprints consisted of the four terminal bases of the transposon flanked by the TA target duplication and led to no major DNA rearrangements. AnMinos transposition depends on the presence of its homologous transposase. Its frequency was not significantly affected by temperature, UV irradiation or the transcription status of the original integration locus (niaD). Importantly, transposition is dependent on nkuA, encoding an enzyme essential for non-homologous end joining of DNA in double-strand break repair. AnMinos proved to be an efficient tool for functional analysis as it seems to transpose in different genomic loci positions in all chromosomes, including a high proportion of integration events within or close to genes. We have used Minos to obtain morphological and toxic analogue resistant mutants. Interestingly, among morphological mutants some seem to be due to Minos-elicited over-expression of specific genes, rather than gene inactivation.
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Affiliation(s)
- Minoas Evangelinos
- Faculty of Biology, University of Athens, Panepistimioupolis, Athens 15784, Greece
| | | | | | | | - Claudio Scazzocchio
- Department of Microbiology, Imperial College London, London SW7 2AZ, United Kingdom; Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Bâtiment 400, 91405 Orsay Cedex, France
| | - George Diallinas
- Faculty of Biology, University of Athens, Panepistimioupolis, Athens 15784, Greece.
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Petit A, Rouleux-Bonnin F, Lambelé M, Pollet N, Bigot Y. Properties of the various Botmar1 transcripts in imagoes of the bumble bee, Bombus terrestris (Hymenoptera: Apidae). Gene 2007; 390:52-66. [PMID: 17088026 DOI: 10.1016/j.gene.2006.07.025] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2006] [Revised: 07/17/2006] [Accepted: 07/18/2006] [Indexed: 11/24/2022]
Abstract
Botmar1 elements are mariner-like elements (MLEs), class II transposable elements that occur in the genome of the bumble bee, Bombus terrestris. Each haploid B. terrestris genome contains about 230 Botmar1, consisting entirely of 1.3-kb and 0.85-kb elements. During their evolution in the B. terrestris genome, two Botmar1 lineages have been differentiated in terms of their nucleic acid sequences and the differences found in their 5' untranslated regions suggest that they could be transcribed differently in B. terrestris. Here, we show that small amounts of Botmar1 mRNA occur in RNA extracts purified from B. terrestris imagoes. This indicates that the Botmar1 transcription is either weak in imagoes, or is restricted to very few cells. The cloning of several mRNAs reveals that only lineage-2 Botmar1 elements are transcribed. This transcription is specific, and uses cardinal initiators and terminators of eukaryotic elements in the Botmar1 elements. The intrastrand stem-loop folds in the mRNA theoretically synthesized by elements of the first lineage suggest that mRNA maintenance in cells might be self-regulated by RNA interference.
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Affiliation(s)
- Agnès Petit
- Laboratoire d'Etude des Parasites Génétiques, FRE-CNRS 2969, Université François Rabelais, UFR des Sciences et Techniques, Bâtiment L, Parc de Grandmont, 37200 Tours, France
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Larrondo LF, Canessa P, Vicuña R, Stewart P, Vanden Wymelenberg A, Cullen D. Structure and transcriptional impact of divergent repetitive elements inserted within Phanerochaete chrysosporium strain RP-78 genes. Mol Genet Genomics 2006; 277:43-55. [PMID: 17033809 DOI: 10.1007/s00438-006-0167-z] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2006] [Accepted: 09/06/2006] [Indexed: 12/01/2022]
Abstract
We describe the structure, organization, and transcriptional impact of repetitive elements within the lignin-degrading basidiomycete, Phanerochaete chrysosporium. Searches of the P. chrysosporium genome revealed five copies of pce1, a ~1,750-nt non-autonomous, class II element. Alleles encoding a putative glucosyltransferase and a cytochrome P450 harbor pce insertions and produce incomplete transcripts. Class I elements included pcret1, an intact 8.14-kb gypsy-like retrotransposon inserted within a member of the multicopper oxidase gene family. Additionally, we describe a complex insertion of nested transposons within another putative cytochrome P450 gene. The disrupted allele lies within a cluster of >14 genes, all of which encode family 64 cytochrome P450s. Components of the insertion include a disjoint copia-like element, pcret3, the pol domain of a second retroelement, pcret2, and a duplication of an extended ORF of unknown function. As in the case of the pce elements, pcret1 and pcret2/3 insertions are confined to single alleles, transcripts of which are truncated. The corresponding wild-type alleles are apparently unaffected. In aggregate, P. chrysosporium harbors a complex array of repetitive elements, at least five of which directly influence expression of genes within families of structurally related sequences.
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Affiliation(s)
- Luis F Larrondo
- Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile and Instituto Milenio de Biología Fundamental y Aplicada, Santiago, Chile
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Fávaro LCDL, Araújo WLD, Azevedo JLD, Paccola-Meirelles LD. The biology and potential for genetic research of transposable elements in filamentous fungi. Genet Mol Biol 2005. [DOI: 10.1590/s1415-47572005000500024] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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Rep M, van der Does HC, Cornelissen BJC. Drifter, a novel, low copy hAT-like transposon in Fusarium oxysporum is activated during starvation. Fungal Genet Biol 2005; 42:546-53. [PMID: 15869889 DOI: 10.1016/j.fgb.2005.03.007] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2004] [Revised: 02/15/2005] [Accepted: 03/21/2005] [Indexed: 10/25/2022]
Abstract
The facultative pathogenic fungus Fusarium oxysporum is known to harbour many different transposable and/or repetitive elements. We have identified Drifter, a novel DNA transposon of the hAT family in F. oxysporum. It was found adjoining SIX1-H, a truncated homolog of the SIX1 avirulence gene in F. oxysporum f. sp. lycopersici. Absence of a target site duplication as well as the 5' part of SIX1-H suggests that transposition of Drifter into the ancestor of SIX1-H was followed by loss of a chromosomal segment through recombination between Drifters. F. oxysporum isolates belonging to various formae speciales harbour between 0 and 5 full-length copies of Drifter and/or one or more copies with an internal deletion. Transcription of Drifter is activated during starvation for carbon or nitrogen.
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Affiliation(s)
- Martijn Rep
- Plant Pathology, Swammerdam Institute for Life Sciences, University of Amsterdam, P.O. Box 94062, 1090 GB Amsterdam, The Netherlands.
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Li Destri Nicosia MG, Brocard-Masson C, Demais S, Hua Van A, Daboussi MJ, Scazzocchio C. Heterologous transposition in Aspergillus nidulans. Mol Microbiol 2004. [DOI: 10.1111/j.1365-2958.2001.02323.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Abstract
The past 10 years have been productive in the characterization of fungal transposable elements (TEs). All eukaryotic TEs described are found including an extraordinary prevalence of active members of the pogo family. The role of TEs in mutation and genome organization is well documented, leading to significant advances in our perception of the mechanisms underlying genetic changes in these organisms. TE-mediated changes, associated with transposition and recombination, provide a broad range of genetic variation, which is useful for natural populations in their adaptation to environmental constraints, especially for those lacking the sexual stage. Interestingly, some fungal species have evolved distinct silencing mechanisms that are regarded as host defense systems against TEs. The examination of forces acting on the evolutionary dynamics of TEs should provide important insights into the interactions between TEs and the fungal genome. Another issue of major significance is the practical applications of TEs in gene tagging and population analysis, which will undoubtedly facilitate research in systematic biology and functional genomics.
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Affiliation(s)
- Marie-Josée Daboussi
- Institut de Génétique et Microbiologie, Université Paris-Sud, F-91405 Orsay cedex, France.
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10
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Lo C, Adachi K, Shuster JR, Hamer JE, Hamer L. The bacterial transposon Tn7 causes premature polyadenylation of mRNA in eukaryotic organisms: TAGKO mutagenesis in filamentous fungi. Nucleic Acids Res 2003; 31:4822-7. [PMID: 12907724 PMCID: PMC169947 DOI: 10.1093/nar/gkg676] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
TAGKO is a Tn7-based transposition system for genome wide mutagenesis in filamentous fungi. The effects of transposon insertion on the expression of TAGKO alleles were examined in Magnaporthe grisea and Mycosphaerella graminicola. Northern analysis showed that stable, truncated transcripts were expressed in the TAGKO mutants. Mapping of the 3'-ends of TAGKO cDNAs revealed that they all contain Tn7 end sequences, regardless of the transposon orientation. Polyadenylation signals characteristic of eukaryotic genes, preceded by stop codons in all frames, are located in both ends of the bacterial transposon. Thus, TAGKO transcripts are prematurely polyadenylated, and truncated proteins are predicted to be translated in the fungal mutants. Depending on the extent of protein truncation, TAGKO mutations in HPD4 (encoding p-hydroxyphenylpyruvate dioxygenase) resulted in tyrosine sensitivity in the two fungi. Similarly, a particular M.grisea CBS1 (encoding cystathionine beta-synthase) TAGKO cDNA failed to complement cysteine auxotrophy in a yeast CBS mutant. TAGKO, therefore, represents a useful tool for in vivo study of truncated gene products in filamentous fungi.
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Affiliation(s)
- Clive Lo
- Paradigm Genetics, Inc., 108 Alexander Drive, Research Triangle Park, NC 27709, USA.
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Trouvelot S, Olivain C, Recorbet G, Migheli Q, Alabouvette C. Recovery of Fusarium oxysporum Fo47 Mutants Affected in Their Biocontrol Activity After Transposition of the Fot1 Element. PHYTOPATHOLOGY 2002; 92:936-45. [PMID: 18944018 DOI: 10.1094/phyto.2002.92.9.936] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
ABSTRACT To investigate the biocontrol mechanisms by which the antagonistic Fusarium oxysporum strain Fo47 is active against Fusarium wilt, a Fot1 transposon-mediated insertional mutagenesis approach was adopted to generate mutants affected in their antagonistic activity. Ninety strains in which an active Fot1 copy had transposed were identified with a phenotypic assay for excision and tested for their biocontrol activity against F. oxysporum f. sp. lini on flax in greenhouse experiments. Sixteen strains were affected in their capacity to protect flax plants, either positively (more antagonistic than Fo47) or negatively (less antagonistic). The molecular characterization of these mutants confirms the excision of Fot1 and its reinsertion in most of the cases. Moreover, we demonstrate that other transposable elements such as Fot2, impala, and Hop have no transposition activity in the mutant genomes. The phenotypic characterization of these mutants shows that they are affected neither in their in vitro growth habit nor in their competitiveness in soil compared with wild-type strain Fo47. These results show that mutants are not impaired in their saprophytic phase and suggest that the altered biocontrol phenotype should likely be expressed during the interaction with the host plant.
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12
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Daboussi MJ, Davière JM, Graziani S, Langin T. Evolution of the Fot1 transposons in the genus Fusarium: discontinuous distribution and epigenetic inactivation. Mol Biol Evol 2002; 19:510-20. [PMID: 11919292 DOI: 10.1093/oxfordjournals.molbev.a004106] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
To understand the evolution of Fot1, a member of the pogo family widely dispersed in ascomycetes, we have performed a phylogenetic survey across the genus Fusarium divided into six sections. The taxonomic distribution of Fot1 is not homogeneous but patchy; it is prevalent in the Fusarium oxysporum complex, absent in closely related sections, and found in five species from the most distant section Martiella. Multiple copies of Fot1 were sequenced from each strain in which the element occurs. In three species, the Fot1 nucleotide sequence is 98% identical to that from F. oxysporum (Fox), whereas nucleotide divergence for host genes is markedly higher: 11% for partial nuclear 28S rDNA and up to 30% for the gene encoding nitrate reductase (nia). In two species, sequence divergence of Fot1-related elements relative to Fox ranged from 7% to 23% (16% average). Most of the sequence differences (82%) were C-to-T and G-to-A transitions. These mutations are distributed throughout the Fot1 sequences, although they tend to be concentrated in the middle portion of the elements. Analysis of the local sequence context of transitions revealed a hierarchy of site preferences. These characteristics are typical of the repeat-induced point mutation process, first discovered in Neurospora crassa. The spotty distribution of Fot1 elements among species together with the high degree of similarity between Fot1 sequences present in distant species strongly suggests a case of horizontal transfer.
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Affiliation(s)
- Marie-Josée Daboussi
- Institut de Génétique et Microbiologie, Bât 400, Université Paris-Sud, 91405 Orsay, France.
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Davière JM, Langin T, Daboussi MJ. Potential role of transposable elements in the rapid reorganization of the Fusarium oxysporum genome. Fungal Genet Biol 2001; 34:177-92. [PMID: 11728156 DOI: 10.1006/fgbi.2001.1296] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The activity of several families of transposable elements (TEs) in the genome of Fusarium oxysporum represents a potential source of karyotypic instability. We investigated transposon-mediated chromosome rearrangements by analyzing the karyotypes of a set of strains in which transposition events had occurred. We uncovered exceptional electrophoretic karyotype (EK) variability, in both number and size of chromosomal bands. We showed that EK differences result from chromosomal translocations, large deletions, and even more complex rearrangements. We also revealed many duplicated chromosomal regions. By following transposition of two elements and analyzing the distribution of different families of TEs on whole chromosomes, we find (i) no evidence of chromosomal breakages induced by transposition, (ii) a clustering of TEs in some regions, and (iii) a correlation between the high level of chromosomal polymorphism and the concentration of TEs. These results suggest that chromosome length polymorphisms likely result from ectopic recombination between TEs that can serve as substrates for these changes.
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Affiliation(s)
- J M Davière
- Institut de Génétique et Microbiologie, UMR 8621, Université Paris-Sud, Orsay Cedex, 91405, France
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Migheli Q, Laugé R, Davière JM, Gerlinger C, Kaper F, Langin T, Daboussi MJ. Transposition of the autonomous Fot1 element in the filamentous fungus Fusarium oxysporum. Genetics 1999; 151:1005-13. [PMID: 10049918 PMCID: PMC1460518 DOI: 10.1093/genetics/151.3.1005] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Autonomous mobility of different copies of the Fot1 element was determined for several strains of the fungal plant pathogen Fusarium oxysporum to develop a transposon tagging system. Two Fot1 copies inserted into the third intron of the nitrate reductase structural gene (niaD) were separately introduced into two genetic backgrounds devoid of endogenous Fot1 elements. Mobility of these copies was observed through a phenotypic assay for excision based on the restoration of nitrate reductase activity. Inactivation of the Fot1 transposase open reading frame (frameshift, deletion, or disruption) prevented excision in strains free of Fot1 elements. Molecular analysis of the Nia+ revertant strains showed that the Fot1 element reintegrated frequently into new genomic sites after excision and that it can transpose from the introduced niaD gene into a different chromosome. Sequence analysis of several Fot1 excision sites revealed the so-called footprint left by this transposable element. Three reinserted Fot1 elements were cloned and the DNA sequences flanking the transposon were determined using inverse polymerase chain reaction. In all cases, the transposon was inserted into a TA dinucleotide and created the characteristic TA target site duplication. The availability of autonomous Fot1 copies will now permit the development of an efficient two-component transposon tagging system comprising a trans-activator element supplying transposase and a cis-responsive marked element.
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Affiliation(s)
- Q Migheli
- Institut de Génétique et Microbiologie, Université Paris-sud, Bâtiment 400, F-91405, France
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