Sporocarps of Endogonales fungi, collected from Japanese forest environments, have been described in previous studies; however, their root colonization has not been fully revealed. To investigate Endogonales diversity in the roots of understory herbaceous plants, we examined fungal partial nuclear small subunit ribosomal DNA amplicons obtained from 13 plant species in five forests. In total, 20 operational taxonomic units (OTU) clustered at 97% sequence similarity were identified and classified into two families, Endogonaceae and Densosporaceae, with most OTUs belonging to the latter. Most OTUs were not closely related to known species; however, some were closely related to plant mycobiont, as reported in previous studies. Although most OTUs were detected in only a few plant species and study sites, one OTU was found in most examined plant individuals. This widespread OTU fungus may play an ecologically important role, but its actual function and morphology remain unknown, requiring further studies.
Teleomorph of Varicosporina prolifera was revealed not to be Corollospora intermedia as suggested formerly, but an undescribed fungus of Corollospora by culturing and phylogenetic study. The true sexual state of V. prolifera is hereby described and a new combined name C. prolifera is proposed. During our studies on marine fungi along the coasts of Japan, an unknown fungus forming clavate conidia was discovered from beaches of Rishiri Island in the northern cool region of Japan and is described here as a new anamorphic species, C. clavata. Regarding the life cycle of Corollospora, 20 species have a teleomorph type life cycle, while in the other eight species, each four are teleomorph-anamorph type and anamorph type, respectively. Phylogenetic analyses revealed three species having Varicosporina anamorphs, C. anglusa, C. prolifera, and C. ramulosa are closely related, and the former two species have the teleomorph-anamorph type life cycles, and the latter one has the anamorph type. Phylogenetic and morphological data suggest that C. anglusa possibly evolved from the teleomorph type ancestor and that C. ramulosa differentiated from the teleomorph-anamorph type ancestor relating to C. prolifera. Similar species differentiation associated with shifting of life cycle types probably occurred in several lineages in Corollospora.
Powdery mildews from the genus Podosphaera infect economically significant crops such as strawberries (Fragaria ×ananassa) and raspberries (Rubus idaeus). Until recently, these powdery mildews have been assigned to Podosphaera aphanis, which represents a complex of species. In the present analysis, selected taxa within Po. aphanis s. lat. have been subjected to morphological and ITS+28S rDNA phylogenetic examinations. We demonstrated that the powdery mildews on Fragaria and Rubus spp. do not pertain to Po. aphanis s. str. The new combination Podosphaera fragariae (≡ Oidium fragariae) is introduced for the powdery mildew on Fragaria ×ananassa, Potentilla spp. and Dasiphora fruticosa. Podosphaera fragariae is widespread in Asia and Europe, however, sequences obtained from specimens collected in South and North America belong to an unresolved group. All sequences obtained from specimens of powdery mildew on Rubus spp. group together in the phylogenetic tree. This suggests a separate species on Rubus spp. for which the new combination Podosphaera ruborum (≡ Oidium ruborum) is introduced. Podosphaera rubi-spectabilis sp. nov. is introduced for powdery mildews from western North America infecting Rubus spectabilis and R. ursinus. Additionally, Po. septentrionalis sp. nov. is introduced for powdery mildews in North America infecting Geum spp. and Agrimonia gryposepala.
Bipolaris maydis, the causal agent of southern corn leaf blight, possesses 10 putative homeobox genes in its genome. In this study, we disrupted and characterized a homeobox gene BmHox7 in B. maydis. While BmHox7 orthologues are required for appressorium formation in Sordariomycetous plant pathogenic fungi (Magnaporthe oryzae, Colletotrichum orbiculare, and C. scovillei), ΔBmHox7 strains formed appressoria normally and exhibited virulence comparable to the wild-type strain. However, in crossing test, ΔBmHox7 strains produced small, immature pseudothecia lacking beaks. Most pseudothecia of BmHox7 mutants contained no asci, indicating that BmHox7 is crucial for sexual reproduction. These findings demonstrate that in B. maydis, BmHox7 is crucial for sexual reproduction but dispensable for appressorial formation and pathogenicity.
The CHK1 MAPK pathway is crucial in appressorium formation and is highly conserved among plant pathogenic fungi. Here, we investigated a putative upstream regulator of this pathway, BmOPY2, in the maize pathogen Bipolaris maydis. Yeast two-hybrid analysis confirmed the interaction between BmOPY2 and BmSTE50, suggesting that BmOPY2 functions as an upstream regulator of the CHK1 MAPK pathway. To investigate the role of BmOPY2 in appressorium formation, we generated BmOPY2-disrupted (∆BmOPY2) mutants. These mutants formed appressoria normally on maize leaves, but did not form them on plastic Petri dishes. This suggests that BmOPY2 regulates appressorium formation via hydrophobic surface recognition but not via recognition of host-derived chemicals. Plant waxes or cutin monomers are recognized by other fungal pathogens, but these substances failed to restore appressorium formation in ∆BmOPY2 mutants. In comparison with the wild type, the ∆BmOPY2 mutants showed increased appressorium formation on intercellular spaces of maize leaves, suggesting that pectin―a component of these spaces―may promote this process. The addition of pectin restored appressorium formation by ∆BmOPY2 mutants on plastic surfaces. These findings reveal a novel dual regulation of appressorium formation in B. maydis, involving both BmOPY2-mediated hydrophobic surface recognition and a distinct pectin-dependent pathway.