Use of molecular cytology to study the structure and biology of phytopathogenic and mycorrhizal fungi

Molecular cytology, that is, the in situ localization of selected molecules by labeling with lectins, enzymes, and antibodies, has made a major contribution to our understanding of the structure and biology of fungi and is increasingly becoming an integral part of molecular, genetic, and biochemical studies. The review presented in this article concentrates on recent advances in the application of molecular cytology in investigations of the structure and biology of phytopathogenic and mycorrhizal fungi and of the molecular basis of their infection of host plants. The review examines details of the structure and molecular composition of fungal cell walls revealed by lectin, enzyme, and antibody labeling. Molecular composition is shown to vary according to taxonomic relationships and as a reflection of differences in cell type, location within the cell, and within thickness of the wall. Sites of synthesis and secretion of wall components are also detected through the labeling of selected molecules. In situ labeling of cytoskeletal elements, microtubules and actin microfilaments, has provided much information on the role of these elements in tip growth, organelle distribution, and spore development. Molecular cytology, particularly through the generation of monoclonal antibodies, has also revealed new and exciting information on specialized infection structures formed by fungi in order to infect host plants. The sites of storage and secretion of adhesives and degradative enzymes have been documented, as have surface specializations that may be associated with avoidance of detection by the host. In addition, in site labeling with enzymes and antibodies has aided studies of the host defense response, including mechanisms of detection of fungal elicitor molecules, changes in wall composition, and the secretion of antifungal compounds. With the increasing production of monoclonal antibodies to fungal molecules, molecular cytology promises to continue to make an important contribution to our understanding of fungal cell structure and function in the future.