High mobility group (HMG-box) genes in the honeybee fungal pathogen Ascosphaera apis

Baylor College of Medicine, Houston, Texas, United States
Mycologia (Impact Factor: 2.47). 07/2007; 99(4):553-61. DOI: 10.3852/mycologia.99.4.553
Source: PubMed


The genome of the honeybee fungal pathogen Ascosphaera apis (Maassen) encodes three putative high mobility group (HMG-box) transcription factors. The predicted proteins (MAT1-2, STE11 and HTF), each of which contain a single strongly conserved HMG-box, exhibit high similarity to mating type proteins and STE11-like transcription factors previously identified in other ascomycete fungi, some of them important plant and human pathogens. In this study we characterized the A. apis HMG-box containing genes and analyzed the structure of the mating type locus (MAT1-2) and its flanking regions. The MAT1-2 locus contains a single gene encoding a protein with an HMG-box. We also have determined the transcriptional patterns of all three HMG-box containing genes in both mating type idiomorphs and discuss a potential role of these transcription factors in A. apis development and reproduction. A multiplex PCR method with primers amplifying mat1-2-1 and Ste11 gene fragments is described. This new method allows for identification of a single mating type idiomorph and might become an essential tool for applied and basic research of chalkbrood disease in honeybees.

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Available from: George Weinstock, Jan 17, 2016
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    • "The C. fimbriata MAT1-2-1 gene was flanked by MAT1-1-1 and a second MAT1-1 gene, MAT1-1-2 (Figure 1A), which is a peculiar arrangement for homothallic fungi. In addition, the SLA2 and APN2 genes usually flank the MAT-1 locus [44]–[47], but in C. fimbriata both were located upstream of MAT1-1-1 where they flanked the APC gene. While the APC gene has been associated with the MAT region in other fungi [36], [48], [49], to the best of our knowledge, it has not previously been reported to be positioned between the genes encoding APN2 and SLA2. "
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    ABSTRACT: Fungi have evolved a remarkable diversity of reproductive strategies. Some of these, most notably those of the model fungi, have been well studied but others are poorly understood. The latter is also true for uni-directional mating type switching, which has been reported in only five fungal genera, including Ceratocystis. Mating type switching allows a self-fertile fungal isolate to produce both self-fertile and self-sterile offspring. This study considered the molecular nature of uni-directional mating type switching in the type species of Ceratocystis, C. fimbriata. To do this, the genome of C. fimbriata was first examined for the presence of mating type genes. Three mating genes (MAT1-1-1, MAT1-2-1 and MAT1-1-2) were found in an atypical organisation of the mating type locus. To study the effect that uni-directional switching has on this locus, several self-sterile offspring were analysed. Using a combination of next generation and conventional Sanger sequencing, it was shown that a 3581 base pair (bp) region had been completely deleted from the MAT locus. This deletion, which includes the entire MAT1-2-1 gene, results in the permanent loss of self-fertility, rendering these isolates exclusively self-sterile. Our data also suggest that the deletion mechanism is tightly controlled and that it always occurs at the same genomic position. Two 260 bp direct repeats flanking the deleted region are strongly implicated in the process, although the exact mechanism behind the switching remains unclear.
    Full-text · Article · Mar 2014 · PLoS ONE
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    • "In this sequencing effort we have identified a transcript contig that is a BLASTX match to an A. capsulatus α-box protein (GenBank accession ABO87596), but does not align to the genome assembly. To determine whether this transcript is part of the A. apis MAT-1 allele, we designed primers to amplify this sequence from genomic DNA, under the assumption that it is flanked by the genes Sla2 and Apn2 as in the MAT-2 idiomorph [8]. "
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    ABSTRACT: We present a comprehensive transcriptome analysis of the fungus Ascosphaera apis, an economically important pathogen of the Western honey bee (Apis mellifera) that causes chalkbrood disease. Our goals were to further annotate the A. apis reference genome and to identify genes that are candidates for being differentially expressed during host infection versus axenic culture. We compared A. apis transcriptome sequence from mycelia grown on liquid or solid media with that dissected from host-infected tissue. 454 pyrosequencing provided 252 Mb of filtered sequence reads from both culture types that were assembled into 10,087 contigs. Transcript contigs, protein sequences from multiple fungal species, and ab initio gene predictions were included as evidence sources in the Maker gene prediction pipeline, resulting in 6,992 consensus gene models. A phylogeny based on 12 of these protein-coding loci further supported the taxonomic placement of Ascosphaera as sister to the core Onygenales. Several common protein domains were less abundant in A. apis compared with related ascomycete genomes, particularly cytochrome p450 and protein kinase domains. A novel gene family was identified that has expanded in some ascomycete lineages, but not others. We manually annotated genes with homologs in other fungal genomes that have known relevance to fungal virulence and life history. Functional categories of interest included genes involved in mating-type specification, intracellular signal transduction, and stress response. Computational and manual annotations have been made publicly available on the Bee Pests and Pathogens website. This comprehensive transcriptome analysis substantially enhances our understanding of the A. apis genome and its expression during infection of honey bee larvae. It also provides resources for future molecular studies of chalkbrood disease and ultimately improved disease management.
    Full-text · Article · Jun 2012 · BMC Genomics
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    • "Ascosphaera apis (Maassen ex Claussen) Spiltoir and Olive (1955) is an important fungal pathogen of the honey bee (Apis mellifera L.) and it is the causal agent of the chalkbrood disease (Gilliam and Vandenberg, 1997). A. apis only produces sexual spores and is heterothallic, thus spores are only produced when mycelia of the two opposite mating types come together and fruiting bodies are formed (Aronstein et al., 2007). The honey bee larvae primarily get infected upon ingesting these spores with their food. "
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    ABSTRACT: Chalkbrood susceptibility of in vitro reared honey bee larvae was investigated. Larvae were grafted from 3–4 colonies headed by pure mated queens of Apis mellifera carnica, A. m. ligustica and A. m. mellifera, respectively. Three day old larvae were fed with different dosages of Ascophaera apis spores and a clear dose-response relationship was shown. Over the whole experiment LD$_{50}$ estimates ranged from 55 to 905 spores. The response differed significantly (up to a factor ten) between colonies of the same subspecies. The mean time to death decreased with increased dose, with more larvae dying faster after eating more fungal spores. The A. m. ligustica larvae used in this study were less susceptible to A. apis than A. m. mellifera and A. m. carnica larvae. However due to the limited number of colonies included and the high variation shown we cannot predict that any A. m. ligustica colony is better adapted to cope with A. apis than colonies of A. m. carnica and A. m. mellifera.
    Full-text · Article · Sep 2009 · Apidologie
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