A fungal conserved gene from the basidiomycete Hebeloma cylindrosporum is essential for efficient ectomycorrhiza formation.

We used Agrobacterium-mediated insertional mutagenesis to identify genes in the ectomycorrhizal fungus Hebeloma cylindrosporum that are essential for efficient mycorrhiza formation. One of the mutants presented a dramatically reduced ability to form ectomycorrhizas when grown in the presence of Pinus pinaster. It failed to form mycorrhizas in the presence of glucose at 0.5 g liter(-1), a condition favorable for mycorrhiza formation by the wild-type strain. However, it formed few mycorrhizas when glucose was replaced by fructose or when glucose concentration was increased to 1 g liter(-1). Scanning electron microscopy examination of these mycorrhizas revealed that this mutant was unable to differentiate true fungal sheath and Hartig net. Molecular analyses showed that the single-copy disrupting T-DNA was integrated 6,884 bp downstream from the start codon, of an open reading frame potentially encoding a 3,096-amino-acid-long protein. This gene, which we named HcMycE1, has orthologs in numerous fungi as well as different other eukaryotic microorganisms. RNAi inactivation of HcMycE1 in the wild-type strain also led to a mycorrhizal defect, demonstrating that the nonmycorrhizal phenotype of the mutant was due to mutagenic T-DNA integration in HcMycE1. In the wild-type strain colonizing P. pinaster roots, HcMycE1 was transiently upregulated before symbiotic structure differentiation. Together with the inability of the mutant to differentiate these structures, this suggests that HcMycE1 plays a crucial role upstream of the fungal sheath and Hartig net differentiation. This study provides the first characterization of a fungal mutant altered in mycorrhizal ability.

Morphological and molecular data for Australian Hebeloma species do not support the generic status of Anamika.

The first collection of a macrofungal agaric species, with morphological features similar to already described Anamika species, has been found in association with animal bones in north Queensland, Australia. This species also shares features with several, commonly occurring and previously described Australian Hebeloma species. An integrated morphological and molecular study has resulted in the conclusion that all Anamika species belong in Hebeloma. As a result, already described species of Anamika are recombined as H. indicum (K.A. Thomas, Peintner, M.M. Moser and Manim.) B.J. Rees & Orlovich, H. angustilamellatum (Zhu L. Yang and Z.W. Ge) B.J. Rees & Orlovich and H. lactariolens (Clémençon and Hongo) B.J. Rees & Orlovich. A. phylogenetic tree based on ribosomal ITS sequences examines the relationship of these species with other Hebeloma species from both hemispheres. Four new species, Hebeloma youngii B.J. Rees, H. nothofagetorum B.J. Rees, H. subvictoriense B.J. Rees, H. lacteocoffeatum B.J. Rees, and one form, H. aminophilum f. hygrosarx B.J. Rees, are described as new from Australia.

Fungal associates of Pyrola rotundifolia, a mixotrophic Ericaceae, from two Estonian boreal forests.

Pyrola rotundifolia (Ericaceae, Pyroleae tribe) is an understorey subshrub that was recently demonstrated to receive considerable amount of carbon from its fungal mycorrhizal associates. So far, little is known of the identity of these fungi and the mycorrhizal anatomy in the Pyroleae. Using 140 mycorrhizal root fragments collected from two Estonian boreal forests already studied in the context of mixotrophic Ericaceae in sequence analysis of the ribosomal DNA internal transcribed spacer region, we recovered 71 sequences that corresponded to 45 putative species in 19 fungal genera. The identified fungi were mainly ectomycorrhizal basidiomycetes, including Tomentella, Cortinarius, Russula, Hebeloma, as well as some ectomycorrhizal and/or endophytic ascomycetes. The P. rotundifolia fungal communities of the two forests did not differ significantly in terms of species richness, diversity and nutritional mode. The relatively high diversity retrieved suggests that P. rotundifolia does not have a strict preference for any fungal taxa. Anatomical analyses showed typical arbutoid mycorrhizae, with variable mantle structures, uniseriate Hartig nets and intracellular hyphal coils in the large epidermal cells. Whenever compared, fungal ultrastructure was congruent with the molecular identification. Similarly to other mixotrophic and autotrophic pyroloids in the same forests, P. rotundifolia shares its mycorrhizal fungal associates with surrounding trees that are likely a carbon source for pyroloids.