RESUMEN
In many fungal pathogens, infection is initiated by conidial germination. Subsequent stages involve germ tube elongation, conidiation, and vegetative hyphal fusion (anastomosis). Here, we used live-cell fluorescence to study the dynamics of green fluorescent protein (GFP)- and cherry fluorescent protein (ChFP)-labeled nuclei in the plant pathogen Fusarium oxysporum. Hyphae of F. oxysporum have uninucleated cells and exhibit an acropetal nuclear pedigree, where only the nucleus in the apical compartment is mitotically active. In contrast, conidiation follows a basopetal pattern, whereby mononucleated microconidia are generated by repeated mitotic cycles of the subapical nucleus in the phialide, followed by septation and cell abscission. Vegetative hyphal fusion is preceded by directed growth of the fusion hypha toward the receptor hypha and followed by a series of postfusion nuclear events, including mitosis of the apical nucleus of the fusion hypha, migration of a daughter nucleus into the receptor hypha, and degradation of the resident nucleus. These previously unreported patterns of nuclear dynamics in F. oxysporum could be intimately related to its pathogenic lifestyle.
Asunto(s)
Núcleo Celular/metabolismo , Fusarium/citología , Fusarium/fisiología , Germinación/fisiología , Hifa/citología , Hifa/fisiología , Esporas Fúngicas/fisiología , Polaridad Celular , Colorantes Fluorescentes/metabolismo , Fusarium/crecimiento & desarrollo , Fusarium/ultraestructura , Proteínas Fluorescentes Verdes/metabolismo , Histonas/metabolismo , Hifa/crecimiento & desarrollo , Solanum lycopersicum/microbiología , Solanum lycopersicum/ultraestructura , Mitosis , Enfermedades de las Plantas/microbiología , Raíces de Plantas/microbiología , Raíces de Plantas/ultraestructura , Esporas Fúngicas/citología , Factores de TiempoRESUMEN
Fusarium species are among the most important phytopathogenic and toxigenic fungi. To understand the molecular underpinnings of pathogenicity in the genus Fusarium, we compared the genomes of three phenotypically diverse species: Fusarium graminearum, Fusarium verticillioides and Fusarium oxysporum f. sp. lycopersici. Our analysis revealed lineage-specific (LS) genomic regions in F. oxysporum that include four entire chromosomes and account for more than one-quarter of the genome. LS regions are rich in transposons and genes with distinct evolutionary profiles but related to pathogenicity, indicative of horizontal acquisition. Experimentally, we demonstrate the transfer of two LS chromosomes between strains of F. oxysporum, converting a non-pathogenic strain into a pathogen. Transfer of LS chromosomes between otherwise genetically isolated strains explains the polyphyletic origin of host specificity and the emergence of new pathogenic lineages in F. oxysporum. These findings put the evolution of fungal pathogenicity into a new perspective.
Asunto(s)
Cromosomas Fúngicos/genética , Fusarium/genética , Fusarium/patogenicidad , Genoma Fúngico/genética , Genómica , Evolución Molecular , Fusarium/clasificación , Interacciones Huésped-Parásitos/genética , Familia de Multigenes/genética , Fenotipo , Filogenia , Proteoma/genética , Análisis de Secuencia de ADN , Sintenía/genética , Virulencia/genéticaRESUMEN
Saponin detoxification enzymes from pathogenic fungi are involved in the infection process of their host plants. Fusarium oxysporum f. sp lycopersici, a tomato pathogen, produces the tomatinase enzyme Tom1, which degrades alpha-tomatine to less toxic derivates. To study the role of the tom1 gene in the virulence of F. oxysporum, we performed targeted disruption and overexpression of the gene. The infection process of tomato plants inoculated with transformants constitutively producing Tom1 resulted in an increase of symptom development. By contrast, tomato plants infected with the knockout mutants showed a delay in the disease process, indicating that Tom1, although not essential for pathogenicity, is required for the full virulence of F. oxysporum. Total tomatinase activity in the disrupted strains was reduced only 25%, leading to beta(2)-tomatine as the main hydrolysis product of the saponin in vitro. In silico analysis of the F. oxysporum genome revealed the existence of four additional putative tomatinase genes with identities to tomatinases from family 3 of glycosyl hydrolases. These might be responsible for the remaining tomatinase activity in the Deltatom1 mutants. Our results indicate that detoxification of alpha-tomatine in F. oxysporum is carried out by several tomatinase activities, suggesting the importance of these enzymes during the infection process.
Asunto(s)
Proteínas Fúngicas/metabolismo , Fusarium/enzimología , Glicósido Hidrolasas/metabolismo , Solanum lycopersicum/microbiología , Cromatografía en Capa Delgada , Proteínas Fúngicas/genética , Fusarium/genética , Fusarium/patogenicidad , Regulación Enzimológica de la Expresión Génica , Regulación Fúngica de la Expresión Génica , Genoma Fúngico , Glicósido Hidrolasas/clasificación , Glicósido Hidrolasas/genética , Isoenzimas/genética , Isoenzimas/metabolismo , Mutación , Filogenia , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Tomatina/análogos & derivados , Tomatina/metabolismo , Virulencia/genéticaRESUMEN
Knockout mutants of Fusarium oxysporum lacking the putative photoreceptor Wc1 were impaired in aerial hyphae, surface hydrophobicity, light-induced carotenogenesis, photoreactivation after UV treatment, and upregulation of photolyase gene transcription. Infection experiments with tomato plants and immunodepressed mice revealed that Wc1 is dispensable for pathogenicity on plants but required for full virulence on mammals.