Mating Type Sequences in Asexually Reproducing Fusarium Species

Abstract

To assess the potential for mating in several Fusarium species with no known sexual stage, we developed degenerate and semidegenerate oligonucleotide primers to identify conserved mating type (MAT) sequences in these fungi. The putative ␣ and high-mobility-group (HMG) box sequences from Fusarium avenaceum, F. culmorum, F. poae, and F. semitectum were compared to similar sequences that were described previously for other members of the genus. The DNA sequences of the regions flanking the amplified MAT regions were obtained by inverse PCR. These data were used to develop diagnostic primers suitable for the clear amplification of conserved mating type sequences from any member of the genus Fusarium. By using these diagnostic primers, we identified mating types of 122 strains belonging to 22 species of Fusarium. The ␣ box and the HMG box from the mating type genes are transcribed in F. avenaceum, F. culmorum, F. poae, and F. semitectum. The novelty of the PCR-based mating type identification system that we developed is that this method can be used on a wide range of Fusarium species, which have proven or expected teleomorphs in different ascomycetous genera, including Calonectria, Gibberella, and Nectria.The genus Fusarium contains filamentous ascomycete fungi with a worldwide distribution. Fusarium species can parasitize cultivated plants (1) and/or produce mycotoxins that pose serious hazards to human and animal health (9, 18). Species of Fusarium can grow successfully on a variety of substrates, can tolerate diverse environmental conditions, and have high levels of intraspecific genetic and genotypic diversity (for examples, see references 8, 12, 17, and 26). Neither the origins of this diversity nor the mechanisms that maintain it are well understood.Meiotic recombination can generate and maintain genotypic variation and result in the reassortment of genes that govern traits such as virulence or toxin production (7). The sexual spores (ascospores) produced by some Fusarium species also may function as infectious propagules (11,19). Although several Fusarium species have a known sexual cycle, i.e., they mate in either a homothallic or heterothallic manner followed by subsequent meiosis and the production of ascospores, important pathogenic species, including Fusarium avenaceum, Fusarium cerealis, Fusarium culmorum, Fusarium equiseti, Fusarium poae, and Fusarium sporotrichioides, have no known sexual stage.Assessing the potential for mating by toxigenic strains of Fusarium would increase our understanding of the genetic mechanisms that maintain intraspecific diversity and biological and evolutionary species integrity. The frequency of sexual reproduction is also an important parameter for the design of strategies to control plant pathogens, since these strategies are often different for clonally and sexually reproducing organisms. High levels of race-specific resistance can be developed in plant cultivars against clonally reproducing organisms, whereas horizontal resistance could be more effective against pathogen...

Tagging target genes of the MAT1-2-1 transcription factor in Fusarium verticillioides (Gibberella fujikuroi MP-A)

“…Filamentous ascomycetes require light for mating and sexual morphogenesis, furthermore, asexual spore production is light-dependent in most fungi. The MAT1-2-1 transcription factor, produced constitutively both in sexually and asexually reproducing Fusarium species (Keré nyi et al 2004) may enhance photoreception in these organisms by up-regulating such an opsin-like protein encoding gene. This stimulating effect could be important under insufficient illumination that frequently occurs in natural habitats of fungi.…”

“…Fungi with no known sexual stage have been reported to contain fully functional, constitutively transcribed MAT genes (Sharon et al 1996;Wirsel et al 1998;Arie et al 2000;Yun et al 2000;Keré nyi et al 2004) indicating that the absence of sexuality in these fungi is not due to adverse mutations of the mating type genes. The reasons of the presence of functional MAT genes in fungi, in which sexual structures have never been observed, are unknown.…”

Association of mating-type with mycelium growth rate and genetic variability of Fusarium culmorum

“…To determine the mating type of F. culmorum isolates, conserved portions of the ALPHA or HMG box of the MAT1-1 and MAT1-2 idiomorph were amplified using degenerate oligonucleotide primer pairs [33]. The PCRs were carried out using a Taq PCR Core Kit (QIAGEN, Inc., Hilden, Germany) as described earlier [2].…”

Asexual Cephalosporin C Producer Acremonium chrysogenum Carries a Functional Mating Type Locus

“…A BLASTX search of the EMBL databases with the cDNA sequence of clone AcEST.4.5311 as the query showed similarity between the sequence of the putative A. chrysogenum ␣-box protein and those of ␣-box mating type proteins of other filamentous ascomycetes. The highest degrees of sequence similarity (with E values of 6eϪ41 and 3eϪ37) were those to MAT1-1-1 of the entomopathogenic fungus Cordyceps takaomontana (anamorphs, Paecilomyces tenuipes and Isaria tenuipes) (77-79) and MAT1-1-1 of the asexual fungal pathogen Fusarium poae (32). By using the sequence of the MAT1-1-2 protein of Cordyceps takaomontana as the query sequence for a TBLASTN search, the product of a 549-bp EST clone (AcEST.4.20371) was found to show the highest degree of sequence identity.…”

“…Among these are plant and human pathogens like Bipolaris sacchari and Aspergillus fumigatus, as well as biotechnologically relevant fungi such as Penicillium chrysogenum and Aspergillus oryzae (3,17,21,26,32,49,50,67,76). Analyses of the genome sequences of the asexual human pathogens Aspergillus fumigatus and Penicillium marneffei and that of Penicillium chrysogenum revealed the presence of transcriptionally active genes associated with sexual reproduction, including genes for pheromone production and recognition (21,26,49,50,76).…”