Article

Structure, Function, and Phylogeny of the Mating Locus in the Rhizopus oryzae Complex

Department of Biology, Duke University, Durham, North Carolina, United States of America.
PLoS ONE (Impact Factor: 3.53). 12/2010; 5(12):e15273. DOI: 10.1371/journal.pone.0015273
Source: PubMed

ABSTRACT The Rhizopus oryzae species complex is a group of zygomycete fungi that are common, cosmopolitan saprotrophs. Some strains are used beneficially for production of Asian fermented foods but they can also act as opportunistic human pathogens. Although R. oryzae reportedly has a heterothallic (+/-) mating system, most strains have not been observed to undergo sexual reproduction and the genetic structure of its mating locus has not been characterized. Here we report on the mating behavior and genetic structure of the mating locus for 54 isolates of the R. oryzae complex. All 54 strains have a mating locus similar in overall organization to Phycomyces blakesleeanus and Mucor circinelloides (Mucoromycotina, Zygomycota). In all of these fungi, the minus (-) allele features the SexM high mobility group (HMG) gene flanked by an RNA helicase gene and a TP transporter gene (TPT). Within the R. oryzae complex, the plus (+) mating allele includes an inserted region that codes for a BTB/POZ domain gene and the SexP HMG gene. Phylogenetic analyses of multiple genes, including the mating loci (HMG, TPT, RNA helicase), ITS1-5.8S-ITS2 rDNA, RPB2, and LDH genes, identified two distinct groups of strains. These correspond to previously described sibling species R. oryzae sensu stricto and R. delemar. Within each species, discordant gene phylogenies among multiple loci suggest an outcrossing population structure. The hypothesis of random-mating is also supported by a 50:50 ratio of plus and minus mating types in both cryptic species. When crossed with tester strains of the opposite mating type, most isolates of R. delemar failed to produce zygospores, while isolates of R. oryzae produced sterile zygospores. In spite of the reluctance of most strains to mate in vitro, the conserved sex locus structure and evidence for outcrossing suggest that a normal sexual cycle occurs in both species.

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    • ") is currently hampered by the lack of appropriate single-copy markers. The biological species recognition concept (Mayr 1982) is difficult to apply in Mucorales because germination of zygospores has been observed in only a few species due to the lengthy period of dormancy and the particular conditions needed for every species (Gryganskyi et al. 2010). Therefore, the production of zygospores has been used instead as a single criterion (e.g. "
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    ABSTRACT: Compensatory base changes (CBCs) in helix II of rDNA ITS2, suggested as a molecular classifier for fungi, were analyzed in Mucor circinelloides and its varieties. Only a few CBCs were found in the complex. Three out of the four accepted formae (f. circinelloides, f. lusitanicus, f. janssenii) did not exhibit CBCs. One CBC was found between strains that form zygospores; consequently, CBC is not always concordant with mating experiments. Strains with two CBC are unable to breed. It is suggested that some strains of the M. circinelloides complex are at the beginning of speciation.
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    • "Mucor irregularis (Schell et al. 2011) or R. arrhizus (Gryganskyi et al. 2010). In R. arrhizus a +/− mating ratio of 1:1 was reported (Gryganskyi et al. 2010), while in R. microsporus this ratio is about 4:1 [32 (+)/8 (−)]. "
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    • "These genes encode for orthologs of the sexM and sexP proteins from the Zygomycetes (e.g. Phycomyces spp., Mucor spp., Rhizopus spp., and Syzygites spp.) (Gryganskyi et al. 2010; Idnurm 2011; Idnurm et al. 2008; Lee et al. 2008); two highly divergent alleles that encode for high mobility group proteins (HMG) associated with sexual identity in this fungal lineage. In the zygomycetes, these alleles have been found surrounded by genes encoding an RNA helicase on one side, and either a triose phosphate transporter or a glutathione oxidoreductase on the other (Idnurm 2011). "
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