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  • Author or Editor: L. HORNOK x
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In this review the organization of fungal chromosomes and the methods used for karyotype analysis are briefly summarized. The role of chromosome rearrangement, supernumerary chromosomes and repeated DNA sequences in the genetic change of fungi is evaluated.

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This work is an extended abstract of a presentation, held at the symposium ‘Non-specific and Specific Innate and Acquired Plant Resistance’ (August 31–September 3, 2006, Budapest, Hungary), devoted to the memory of the late Professor Dr. Zoltán Klement, member of the Hungarian Academy of Sciences. Fusarium species use different reproduction strategies, ranging from frequent heterothallic mating to clonal reproduction. Mating type genes, the major regulators of sexual reproduction are fully functional in “asexual” members of the genus and they may affect important events not only in the sexual but also in the asexual phase of the life cycle of these fungi. Female sterility, a lesser known trait, which greatly influences the frequency of mating and meiotic recombination in fungi, is also affected by genes not directly related to sexual reproduction.

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Conidium production was significantly reduced in three independent ΔFvMAT1-2-1 gene disruption mutants of F. verticillioides as compared to the wild type parental strain, when fungi were incubated on carrot agar either under diurnal illumination conditions or in total darkness. The conidiation specific con10 gene was expressed constitutively at low levels in the wild type strain, whereas levels of con10 transcripts were drastically reduced in the the ΔFvMAT1-2-1/M15 mutant. These findings demonstrate that mutants, lacking the functional mat1-2-1 mating type gene have lost not only their sexual reproduction capability, but became also retarded in asexual sporulation indicating that mating type genes have positive functions during the asexual phase of the fungal life cycle.

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Expression patterns of cel5A and cel5B , two endoglucanase encoding genes of Thermobifida fusca were compared by quantitative real-time PCR. With Avicel as carbon source the transcript level of cel5A continuously increased until the 10 th hour of incubation and then a sharp decrease was observed, whereas cel5B presented a slow constitutive expression on this substrate. When the microcrystalline cellulose powder MN300 was used as the inducing carbon source, the expression patterns of the two genes were similar. A low initial level of expression was followed by a rapid increase at the 5 th hour of incubation; a transient repression was then observed at the 10 th hour but after this sampling time, the expression levels started to increase again. The relative expression levels of cel5A were always higher than those of cel5B . Differences in transcription patterns of these two genes can be explained with the imperfect structure of the CelR binding regulatory region of cel5B .

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Species-specific PCR assay was used to monitor endophytic colonization of maize by F. proliferatum. The fungus could be detected in all parts of one-week-old seedlings, grown in artificially infected soil indicating that F. proliferatum entered into the host tissues during germination. However, the extent of colonization gradually decreased and by the third week no signs of infection were detected in any part of the plants. These findings confirmed that F. proliferatum is a weak pathogen of maize and the damage reportedly caused by this species originates from horizontal transmission of the fungus rather than from an unbalanced endophytic interaction.

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Fphog1 , a HOG-type mitogen-activated protein kinase (MAPK) encoding gene of Fusarium proliferatum was constitutively expressed in all types of fungal cells. Δ Fphog1 mutants grew normally on artificial media; sporulation and spore germination were also normal. The mating capability of M24, a representative strain of the Δ Fphog1 mutants, showed no detectable decline, indicating that this HOG-type MAPK gene is dispensable for growth and reproduction under optimal culture conditions. Strain M24 had increased tolerance to vinclozoline and fludioxonil fungicides. Invasive growth of the wild type and three Δ Fphog1 gene replacement mutants (M21, M24, M36) were assessed on tomato fruits. All strains behaved similarly, i.e. they produced visible symptoms on the second day after infection, and produced ∼3 cm lesion, overgrown by fungal mycelium after six days of incubation. These data suggest that the HOG-type MAPK pathway is not required for the invasive growth of this fungus.

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Dermacentor reticulatus is a tick species of high medical and veterinary importance, emerging in several parts of Europe. Up to now most studies focusing on zoonotic rickettsiae in D. reticulatus were based on ticks collected in a limited part of the questing period, and did not take into account the potential seasonal variations in the rate of infection with tick-borne rickettsiae. The aim of the present study was to investigate the latter phenomenon, i.e. to screen D. reticulatus adults, collected monthly in two urban habitats of Budapest, for the presence of three zoonotic Rickettsia spp. Altogether 852 D. reticulatus adults were collected, which showed significantly similar seasonal activity in the two evaluated habitats. Among the 413 molecularly analysed ticks, R. helvetica-infected D. reticulatus were only collected during autumn in habitat-1, in contrast to habitat-2. The overall prevalence of R. raoultii in D. reticulatus adults was significantly higher in habitat-1 than in habitat-2. In addition, the seasonal distribution of R. raoultii-infected ticks was different between the two habitats (in habitat-2 significantly more R. raoultii-infected ticks were collected in the autumn, in comparison with winter and spring). Rickettsia slovaca was not detected in any of the molecularly analysed ticks. The results clearly indicate that a single-time or seasonally biased collection of D. reticulatus adults and their subsequent molecular analysis may not be informative on the real prevalence of rickettsiae. This is because the availability/ activity of infected ticks shows significant seasonal fluctuations, both within and between habitats. Instead, for screening D. reticulatus-borne rickettsiae, it is important to collect monthly samples and then to assess seasonal prevalence and actual habitat-associated eco-epidemiological risks.

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Fvwc1 and Fvwc2, orthologues of the wc-1 and wc-2 genes encoding for proteins of the white collar complex (WCC) in Neurospora crassa were cloned from Fusarium verticillioides and lack-of-function wc mutants were obtained by targeted gene disruption. Photo-conidiation was found to be absent in F. verticillioides, on the contrary, the wild type strain produced less conidia under continuous illumination than in the dark. Inactivation of any of the wc genes led to total female sterility, without affecting male fertility or asexual conidiation. No loss in colonization capability/invasive growth of the wc mutants was observed, when assessed on tomato fruits. Both Fvwc1 and Fvwc2 showed constitutive expression in the wild type cultures incubated in the dark and exposure to light caused only negligible increases in their transcription. Both Fvwc1 and Fvwc2 were down-regulated in a ΔFvmat1-2-1 gene disruption mutant, lacking a functional mating type (mat1-2-1) gene, suggesting that the MAT1-2-1 product has a positive regulatory effect on the white collar genes.

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