Biomedical subjects

Karl-Heinz Rexer

Publications and source records attributed to Karl-Heinz Rexer.

3 recordsLinked to original sources

PubMed2006

Gene expression analysis of arbuscule development and functioning.

The arbuscular mycorrhiza (AM) is characterized by specific morphological structures of the fungus and the plant and by physiological adaptations which are mostly beneficial for both partners of the symbiosis. This review describes approaches to study the molecular basis of the interaction. RNA accumulation patterns have been monitored in Pisum sativum to analyse the plant response to arbuscule development. In a direct approach, the Mtha1 gene from Medicago truncatula was cloned which is expressed in arbusculated cells of M. truncatula. The gene putatively encodes an H(+)-ATPase involved in the improved plant nutrition during mycorrhization. Finally, a tripartite system between M. truncatula, Glomus mosseae and Aphanomyces euteiches was established, in order to study bioprotection. Analysis of the transcriptome has been started to analyse the interaction between the plant, the pathogen and the AM fungus.

Gene Expression Regulation, Plant↗

PubMed2006

Morphology and metamorphosis of the peptidergic Va neurons and the median nerve system of the fruit fly, Drosophila melanogaster.

Metamorphosis is a fundamental developmental process and has been intensively studied for various neuron types of Drosophila melanogaster. However, detailed accounts of the fate of identified peptidergic neurons are rare. We have performed a detailed study of the larval morphology and pupal remodelling of identified peptidergic neurons, the CAPA-expressing Va neurons of D. melanogaster. In the larva, Va neurons innervate abdominal median and transverse nerves that are typically associated with perisympathetic organs (PSOs), major neurohaemal release sites in insects. Since median and transverse nerves are lacking in the adult, Va neurites have to undergo substantial remodelling during metamorphosis. We have examined the hitherto uncharacterised gross morphology of the thoracic PSOs and the abdominal median and transverse nerves by scanning electron microscopy and found that the complete reduction of these structures during metamorphosis starts around pupal stage P7 and is completed at P9. Concomitantly, neurite pruning of the Va neurons begins at P6 and is preceded by the high expression of the ecdysone receptor (EcR) subtype B1 in late L3 larvae and the first pupal stages. New neuritic outgrowth mainly occurs from P7-P9 and coincides with the expression of EcR-A, indicating that the remodelling of the Va neurons is under ecdysteroid control. Immunogold-labelling has located the CAPA peptides to large translucent vesicles, which are released from the transverse nerves, as suggested by fusion profiles. Hence, the transverse nerves may serve a neurohaemal function in D. melanogaster.

Animals↗

PubMed2004

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.

Basidiomycota↗