The fate of mitochondria after infection of the Mucoralean fungus Absidia glauca by the fusion parasite Parasitella parasitica: comparison of mitochondrial genomes in zygomycetes.

Absidia glauca and Parasitella parasitica constitute a versatile experimental system for studying horizontal gene transfer between a mucoralean host and its fusion parasite. The A. glauca chondriome has a length of approximately 63 kb and a GC content of 28%. The chondriome of P. parasitica is larger, 83 kb, and contains 31% GC base pairs. These mtDNAs contain the standard fungal mitochondrial gene set, small and large subunit rRNAs, plus ribonuclease P RNA. Comparing zygomycete chondriomes reveals an unusually high number of homing endonuclease genes in P. parasitica, substantiating the mobility of intron elements independent of host-parasite interactions.

Post-translational regulation by structural changes of 4-dihydromethyltrisporate dehydrogenase, a key enzyme in sexual and parasitic communication mediated by the trisporic acid pheromone system, of the fungal fusion parasite Parasitella parasitica.

Sexual communication between complementary mating partners in the fungal group of zygomycetes is mediated by the trisporoid pheromone system. A key enzyme towards biosynthesis of hormonally active trisporoids is 4-dihydromethyltrisporate dehydrogenase (TSP1), an enzyme occurring in all zygomycetous fungi. Trisporic acid and some of its precursor molecules serve as pheromones for recognizing complementary mating partners and for induction of the differentiation program towards sexual spore formation. In the parasitic zygomycete Parasitella parasitica, a biotrophic fusion parasite infecting many other zygomycetes, these substances have an additional function: They are also responsible for host-parasite recognition and the formation of the characteristic infection structures. Parasitic interactions are mating type dependent as well. In the Mucor-related mycoparasite P. parasitica we can study both types of communication in parallel. We were interested in protein structures of TSP1 from P. parasitica, the genome of which was recently sequenced by us, and especially in the mechanisms involved in the switch from sexual to parasitic communication. P. parasitica contains at least six genes coding for TSP1-like proteins. We created models of tertiary structures and performed protein-protein docking with the resulting protein structures to simulate dimerization and to provide support for probable regulatory mechanisms at the protein level. The resulting structure models show differences in putative activity and binding preferences between the different TSP1-like proteins. Two of them seem to be able to form solid binding pockets for substrate and cosubstrate after dimerization. The other four TSP1-like proteins are more likely to represent regulating subunits for the two active isoforms. The ability to form homodimers with enzymatic activity could be the crucial difference between sexual and parasitic communication pathways. TSP1 PARPA_07791 forms enzymatically inactive homodimers. The second TSP1, PARPA_04105, forms active homodimers and could be responsible for the parasitic pathway of communication. Both TSP1 proteins can form more or less active heterodimers with the additional TSP1-like proteins. TSP1 PARPA_07791 mediates the sexual pathway probably as in other zygomycetous fungi like Mucor mucedo. High sequence identities between this TSP1 isomer and TSP1 proteins from other zygomycetes substantiate its function. This bioinformatic study supports previous experimental findings of post-translational regulation of 4-dihydromethyltrisporate dehydrogenases in zygomycetes and, for the first time, provides a substantiated hypothesis of the underlying mechanism.

Complete Mitochondrial DNA Sequence of the Mucoralean Fungus Absidia glauca, a Model for Studying Host-Parasite Interactions.

The mitochondrial DNA (mtDNA) ofAbsidia glaucahas been completely sequenced. It is 63,080 bp long, has a G+C content of 28%, and contains the standard fungal gene set.A. glaucais the recipient in a laboratory model for horizontal gene transfer withParasitella parasiticaas a donor of nuclei and mitochondria.

Complete Mitochondrial DNA Sequence of the Mucoralean Fusion Parasite Parasitella parasitica.

The complete mitochondrial DNA sequence of the Mucor-related fungus Parasitella parasitica has been sequenced. It has a G+C content of 30% and a total length of 83,361 bp. All protein-coding genes normally found in fungi are present in the sequence. A special feature is the remarkably high number of 27 homing endonucleases.

Mating type gene homologues and putative sex pheromone-sensing pathway in arbuscular mycorrhizal fungi, a presumably asexual plant root symbiont.

The fungal kingdom displays a fascinating diversity of sex-determination systems. Recent advances in genomics provide insights into the molecular mechanisms of sex, mating type determination, and evolution of sexual reproduction in many fungal species in both ancient and modern phylogenetic lineages. All major fungal groups have evolved sexual differentiation and recombination pathways. However, sexuality is unknown in arbuscular mycorrhizal fungi (AMF) of the phylum Glomeromycota, an ecologically vital group of obligate plant root symbionts. AMF are commonly considered an ancient asexual lineage dating back to the Ordovician, approximately 460 M years ago. In this study, we used genomic and transcriptomic surveys of several AMF species to demonstrate the presence of conserved putative sex pheromone-sensing mitogen-activated protein (MAP) kinases, comparable to those described in Ascomycota and Basidiomycota. We also find genes for high mobility group (HMG) transcription factors, homologous to SexM and SexP genes in the Mucorales. The SexM genes show a remarkable sequence diversity among multiple copies in the genome, while only a single SexP sequence was detected in some isolates of Rhizophagus irregularis. In the Mucorales and Microsporidia, the sexM gene is flanked by genes for a triosephosphate transporter (TPT) and a RNA helicase, but we find no evidence for synteny in the vicinity of the Sex locus in AMF. Nonetheless, our results, together with previous observations on meiotic machinery, suggest that AMF could undergo a complete sexual reproduction cycle.

Correlation between sequence, structure and function for trisporoid processing proteins in the model zygomycete Mucor mucedo.

Terpenoids, steroids, carotenoids, phytoenes and other chemically related substance groups fulfill multiple functions in all realms of the organismic world. This analysis focuses on trisporoids that operate as pheromones in the phylogenetically ancient fungal group of mucoralean zygomycetes. Trisporoids serve as pheromones for recognizing complementary mating partners and for inducing the differentiation program towards sexual spore formation. Trisporoids are synthesized by oxidative degradation of ß-carotene. Structurally, they are related to retinoids in mammals and abscisic acid in vascular plants. In order to evaluate evolutionary relationships between proteins involved in trisporoid binding and also for checking possibilities to recognize functionally related proteins by sequence and structure comparisons, we compared representative proteins of different origins. Towards this goal, we calculated three-dimensional structures for 4-dihydromethyltrisporate dehydrogenase (TSP1) and 4-dihydrotrisporin dehydrogenase (TSP2), the two proteins involved in trisporic acid synthesis that have unequivocally been correlated with their catalytic function for the model zygomycete Mucor mucedo. TSP1 is an aldo-keto reductase with a TIM-barrel structure, TSP2 belongs to short-chain dehydrogenases, characterized by a Rossmann fold. Evidently, functional conservation, even implying very similar substrates and identical cosubstrates of enzymes in a single organism, turns out to be essentially independent of basic protein structure. The binding sites for NADP and trisporoid ligands in the proteins were determined by docking studies, revealing those regions affecting substrate specificity. Despite the pronounced differences in amino acid sequence and tertiary structure, the surfaces around the active sites are comparable between TSP1 and TSP2. Two binding regions were identified, one sterically open and a second closed one. In contrast to TSP1, all docking models for TSP2 place the trisporoid into the second, channel-like region.