Kiminori Shimizu

STRUCTURAL ANALYSIS OF PKS1, A POLYKETIDE SYNTHASE GENE INVOLVED IN MELANIN BIOSYNTHESIS IN COLLETOTRICHUM LAGENARIUM

Albino mutants (Pks−) of Colletotrichum lagenarium form nonmelanized appressoria and possess little penetrating ability on the host plant. The defect in albino mutant 79215 (Pks−) is considered to lie in pentaketide biosynthesis and/or pentaketide cyclization during melanin biosynthesis. The cosmid pAC7, carrying the PKS1 gene, when transformed into the albino mutant restores the wild-type melanin phenotype. We have determine the DNA sequence and the transcriptional organization of the PKS1 gene. The PKS1 gene contains one open reading frame, consisting of 3 exons separated by two short introns. The predicted PKS1 polypeptide consists of 2187 amino acids and shows significant similarities with other polyketide synthases, particularly that encoded by wA in Aspergillus nidulans, involved in conidial pigmentation. The PKS1 gene contains highly conserved β-ketoacyl synthase, acetyl/malonyl transferase, and acyl carrier protein domains. We propose that the C. lagenarium PKS1 gene encodes a polyketide synthase involved in melanin biosynthesis.

Genetic analysis of Cochliobolus heterostrophus polyoxinresistant mutants

Nine polyoxin-resistant mutants ofCochliobolus heterostrophus were isolated after ethyl methanesulphonate mutagenesis. All were highly resistant to polyoxin (MIC≥1,600 ppm). Crosses between the mutants and a wild-type strain revealed that the resistance trait was inherited to the offsprings in different fashions. Four of the mutant strains inherited polyoxin resistance in a 1∶1 segregation ratio, indicating that the phenotypes in these strains were due to alteration at a single locus. Allelism tests revealed four new loci,Pol1, Pol2, Pol3 andPol4, for polyoxin resistance in these mutant strains. The genes responsible for the phenotypes of the other five mutant strains were not determined, because of extremely slow growth of progenies in one cross, sterility in another cross, and inexplicable responses to polyoxin of the progenies in the other crosses. No linkage was detected between the genes for polyoxin resistance and mating type.

Genetic analyses of Cochliobolus heterostrophus albino mutant with deficiencies at two loci

A new class of albino mutant ofCochliobolus heterostrophus was isolated. Its colony color was indistinguishable from that of albino mutants previously reported. Application of the melanin intermediate scytalone induced this mutant to pigment slightly, but not completely. Genetic analyses showed that the mutant had two deficient genes. When only one of these genes was deficient, the colony color was indistinguishable from the wild type, whereas deficiency of both genes resulted in the albino phenotype. These deficiencies lie upstream of scytalone biosynthesis. These genes were designated asCal1 andCal2.

Coprinopsis neophlyctidospora sp. nov., a new ammonia fungus from boreal forests in Canada

Coprinopsis neophlyctidospora sp. nov. (Basidiomycota, Agaricales), collected in urea treated soil of boreal forests from Canada is described and illustrated. Its micromorphological features, phylogenetic analysis, and mating test delineate this taxon as a new species. In addition, its ecological characters also indicate it is a new ammonia fungus.

Polyoxin Resistance of Reddish Brown Laboratory Mutants of Cochliobolus heterostrophus

Six reddish brown polyxin-resistant mutants of Cochliobolus heterostrophus were isolated after ethyl methanesul-phonate and N-nitroquinoline oxide mutageneses followed by selection on polyoxin. All the mutants were highly resistant to polyoxin (MIC > 1600 μg/ml). When mutants were crossed with the wild-type strain, all crosses had a 1 : 1 ratio of mutant (reddish brown pigmentation and polyoxin resistance) : wild type (non-reddish brown pigmentation and polyoxin sensitivity), indicating that the phenotypes in these strains were due to alteration at a single gene locus in each strain. Allelism tests revealed the existence of two loci, Pol2 and Pol5. The results of the crossing and mutation-rate studies suggest that the each gene was pleiotropic for the reddish brown color and polyoxin resistance.

Pheromone Studies on Astigmatid Mites: Recent Progress – A Comparison of Molecular Phylogeny, Distribution and Function of Female Sex Pheromone in Caloglyphus spp. (Acarina: Acaridae)

Abstract Female sex pheromones, which elicit mounting behavior of conspecific males, were identified in 4 species of the genus Caloglyphus (Acarina: Acaridae). Although the sex pheromones are distributed over both males and females, they could be classified into two groups; one is an adult-specific pheromone, and the other is one that is detectable even in nymphal stages. In addition, in the adult-specific species, the pheromonal content ratios of female to male were found to be larger than those observed in the nonspecific species. The two types of pheromonal distribution were compared with phylogenetic relationships based on a portion of the mitochondrial cytochrome oxidase subunit I (COI) gene in the four species. The polymerase chain reaction was used to amplify the COI from the four mites, with primers used in spider mites (Tetranychidae). Fragments of the COI (453 bp) were obtained for the three species. The phylogenetic tree, based on the COI sequences, was inferred using a maximum parsimony method. Analysis of the pheromonal distribution within this phylogenetic framework agreed with the hypothesis that the mite sex pheromone evolved from a common compound, which originally functioned as a male sexual excitant, into a biologically active, sex linked specific one.