Karl-Heinz Rexer

Piriformospora indica, gen. et sp. nov., a new root-colonizing fungus.

A new fungus isolate was discovered in an arbuscular mycorrhizal fungal spore from a desert soil in India. It could easily be cultivated on various synthetic media, and formed pear-shaped chlamydos...

Sebacinales: a hitherto overlooked cosm of heterobasidiomycetes with a broad mycorrhizal potential*

Within the basidiomycetes, the vast majority of known mycorrhizal species are homobasidiomycetes. It was therefore surprising when molecular and ultrastructural studies revealed a broad diversity of mycorrhizal associations involving members of the heterobasidiomycetous Sebacinaceae, fungi which, due to their inconspicuous basidiomes, have been often overlooked. To investigate the phylogenetic position of the Sebacinaceae within the basidiomycetes and to infer phylogenetic relationships within the Sebacinaceae, we made molecular phylogenetic analyses based on nuclear rDNA. We present a well-resolved phylogeny of the main lineages of basidiomycetes which suggests that the Sebacinaceae is the most basal group with known mycorrhizal members. Since more basal taxa of basidiomycetes consist of predominantly mycoparasitic and phytoparasitic fungi, it seems possible that a mycorrhizal life strategy, which was transformed into a saprotrophic strategy several times convergently, is an apomorphic character for the Hymenomycetidae. Mycorrhizal taxa of Sebacinaceae, including mycobionts of ectomycorrhizas, orchid mycorrhizas, ericoid mycorrhizas, and jungermannioid mycorrhizas, are distributed over two subgroups. One group contains species with macroscopically visible basidiomes, whereas members of the other group probably lack basidiomes. Sebacina appears to be polyphyletic; current species concepts in Sebacinaceae are questionable. Sebacina vermifera sensu Warcup & Talbot consists of a broad complex of species possibly including mycobionts of jungermannioid and ericoid mycorrhizas. This wide spectrum of mycorrhizal types in one fungal family is unique. Extrapolating from the known rDNA sequences in Sebacinaceae, it is evident that there is a cosm of mycorrhizal biodiversity yet to be discovered in this group. Taxonomically, we recognise the Sebacinaceae as constituting a new order, the Sebacinales.

Multinucleated smooth muscles and mononucleated as well as multinucleated striated muscles develop during establishment of the male reproductive organs of Drosophila melanogaster

The adult musculature in D. melanogaster forms during metamorphosis. Much is known about the flight and leg musculature, but not about the muscles surrounding the male reproductive tract. The inner genitalia of males consist of the testes, which emerge from the gonads; the remaining genital organs, i.e., paragonia (or accessory glands), ejaculatory duct, sperm pump, and seminal vesicles, develop out of the genital imaginal disc. We analyzed the myoblasts forming the muscle layers of these organs. In myoblasts derived from the genital imaginal disc, the regulatory region of the transcription factor DMef2 is active. DMef2 is also needed for specification and differentiation of embryonic and adult myoblasts. We could discriminate three different muscle types: (i) multinucleated muscles that resemble vertebrate smooth muscles surround the testes, (ii) multinucleated muscles that resemble striated muscles comprises seminal vesicles and the sperm pump, and (iii) mononucleated striated musculature encloses the paragonia and ejaculatory duct. Members of the immunoglobulin superfamily involved in embryonic myogenesis, Dumbfounded (Duf) and Sticks and Stones (Sns), were also expressed in the genital imaginal disc, in the muscle sheath of the testes during muscle differentiation and in the secretory secondary cells, which are part of the binucleated epithelia enclosing the paragonia.

Colonization of roots of cultivated Solanum lycopersicum by dark septate and other ascomycetous endophytes

Tomato (Solanum lycopersicum L.) roots from four different crop sites in Colombia were surface sterilized and 51 fungal isolates were obtained and conserved for further analysis. Based on microscopical observations and growth characteristics, 20 fungal isolates corresponded to genus Fusarium, six presented asexual conidia different from Fusarium, eight were sterile mycelia, seven of which had dark septate hyphae and 17 did not continue to grow on plates after being recovered from conservation. Growth on different media, detailed morphological characterization and ITS region sequencing of the six sporulating and eight sterile isolates revealed that they belonged to different orders of Ascomycota and that the sterile dark septate endophytes did not correspond to the well known Phialocephala group. Interactions of nine isolates with tomato plantlets were assessed in vitro. No effect on shoot development was revealed, but three isolates caused brown spots in roots. Colonization patterns as analyzed by confocal microscopy differed among the isolates and ranged from epidermal to cortical penetration. Altogether 11 new isolates from root endophytic fungi were obtained, seven of which showed features of dark septate endophytes. Four known morphotypes were represented by five isolates, while six isolates belonged to five morphotypes of putative new unknown species.

The taxonomic foundation, species circumscription and continental endemisms of Singerocybe: evidence from morphological and molecular data

The genus Singerocybe (Tricholomataceae, Agaricales, Basidiomycota) has been the subject of controversy since its proposal in 1988. Its taxonomic foundation, species circumscription and geographical distribution have not yet been examined with molecular sequence data. In this study phylogenetic analyses on this group of fungi were conducted based on collections from Europe, eastern Asia, southern Asia, North America and Australia, with four nuclear markers, ITS, nrLSU, tef1-α and rpb2. Molecular phylogenetic analyses, together with morphological observations, strongly support Singerocybe as a monophyletic group and identify the vesicles in the pileal and stipe cuticle as a synapomorphy of this genus. Seven species are recognized in the genus, including one new species and four new combinations. Clitocybe trogioides and Clitocybe trogioides var. odorifera are synonyms of Singerocybe humilis and Singerocybe alboinfundibuliformis respectively. Most of these species are geographically restricted in their distributions. Furthermore our study expands the distribution range of Singerocybe from the North Temperate Zone to Australia (Tasmania) and tropical southern Asia.

Morphology and Ultrastructure of Piriformospora indica

A review is given about the morphological and ultrastructural characters of Piriformospora indica. The morphology of hyphal cells, mycelial, and chlamydospores are described in detail. Piriformospora is able to form different types of interactions with plant groups mosses, ferns, and gymno- and angiosperms. A survey of the tested host plants is given. The morphology of interacting hyphae and root cells depends on the plant species. Besides the mutualistic mode of life, Piriformospora indica is able to live as an endophytic fungus; under specific conditions, this species can behave as a necrotrophic fungus. All these different characters of the plant growth-promoting fungus, Piriformospora indica, indicate that this species is very valuable for basic research and a wide spectrum of applications in agriculture and horticulture.

Six newly developed microsatellite markers of Laccaria amethystina, using an improved CSSR approach

Microsatellite markers were established by an improved combined simple sequence repeat (CSSR) approach for the ectomycorrhizal basidiomycete Laccaria amethystina. Six markers delivered codominant polymorphic results, with up to six different alleles. They were tested with DNA originating from sporocarps and ectomycorrhizal root tips from silver fir (Abies alba), collected in the northern Black Forest. Sporocarps and ectoymcorrhizae exhibited similar allelic profiles, without any distorting influence of the host tree species. Results were compared to allelic profiles delivered by three published Asian markers. Allelic frequencies of the new markers showed a higher resolution of individuals within the population community, but partially a lower grade of heterozygosity. Possible reasons are discussed, and further questions addressed.

A new Laccaria species from cloud forest of Fortuna, Panama

A new species of Agaricales, called Laccaria stellata, was collected in a premontane cloud forest in the Fortuna Forest Reserve, Panama, and it is described based on morphological and molecular characteristics. It differs morphologically from all known species of Laccaria by minute, pinkish-orange colored basidiomata, a very thin and translucent pileus, very distant lamellae, 4-spored basidia, and globose basidiospores covered by relatively large echinulae. Molecular rDNA sequence data confirm the separation of this new species from other Laccaria species for which rDNA sequence data are available.

The syncytial visceral and somatic musculature develops independently of β3-Tubulin during Drosophila embryogenesis, while maternally supplied β1-Tubulin is stable until the early steps of myoblast fusion.

Microtubules are necessary for fusion and elongation of vertebrate muscle cells. In Drosophila, several isoforms of β-Tubulin, the functional subunit of microtubules, are expressed in different tissues of the developing embryo, while solely the β3-Tubulin isoform is detected in large amounts during differentiation of the somatic and visceral musculature. Here we show the unexpected result that all mesodermal tissues develop correctly in β3-Tubulin loss of function mutants. Furthermore, we show that β2-Tubulin transcripts are not detectable in embryos and an exceptional zygotic β1-Tubulin expression in β3-Tubulin mutants cannot be observed. Nevertheless, a maternally contributed β1-Tubulin-GFP fusion protein (from protein trap collection, Buszczak et al., 2007, Genetics 175, 1505-1531) acts in a dominant negative way, disturbing embryonic development from early stages on. This effect can be observed to the same extent in a zygotic β3-Tubulin mutant situation. Our results indicate that the maternally supplied β1-Tubulin based microtubule network is sufficient for myoblast fusion, myotube elongation and sarcomere formation both during visceral and somatic muscle development in Drosophila embryogenesis.

The ontogeny of the fruit bodies of Mycena stylobates

The ontogeny of the fruit bodies of Mycena stylobates was studied by light microscopy and scanning electron microscopy (SEM). The ontogeny was divided into two phases: first the primordium with all the structures of the mature fruit body was established, then the primordial stipe elongated rapidly and the exposed hymenium started producing spores immediately. The first detected stage of fruit body formation was an irregularly arranged hyphal structure within the substrate colonized. After the rupture of the surface of the substrate, the primordium established on the surface. Soon a layer of wrapping hyphae was differentiated, which covered the complete primordium. The structures of the stipe and the cap developed synchronously. The developing stipe, cap and basal disc together formed a secondary ring-like cavity, in which the development of the hymenophore took place. The lower side of the cap was covered by a layer of degenerated hyphae. The development of the hymenophore started with a number of small alveolae on the lower side of the cap, which were covered with a hymenophoral palisade. The margins of these alveolae formed the primary lamellae, which in the first stage of their development were covered by a layer of degenerated hyphae. The hymenophoral palisade spread from the developing alveolae to the lamellar edge; the edge of the primary lamellae was forked in the early stages. Secondary lamellae were formed by the down folding of ridges from the lower side of the cap. In contrast to the primary lamellae, they were covered with hymenophoral palisade from the beginning. Spore production started immediately after the elongation of the stipe. These results were compared with other known modes of ontogeny within the Agaricales and some comments on the terminology used for the description of basidiome morphogenesis are made.