Contributions of Ultrastructural Studies to the Knowledge of Filamentous Fungi Biology and Fungi-Plant Interactions.

Franco Faoro,Raffaella Balestrini,Antonella Faccio

doi:10.3389/ffunb.2021.805739

Abstract

Since the first experiments in 1950s, transmission electron microscopy (TEM) observations of filamentous fungi have contributed extensively to understand their structure and to reveal the mechanisms of apical growth. Additionally, also in combination with the use of affinity techniques (such as the gold complexes), several aspects of plant-fungal interactions were elucidated. Nowadays, after the huge of information obtained from -omics techniques, TEM studies and ultrastructural observations offer the possibility to support these data, considering that the full comprehension of the mechanisms at the basis of fungal morphogenesis and the interaction with other organisms is closely related to a detailed knowledge of the structural features. Here, the contribution of these approaches on fungal biology is illustrated, focusing both on hyphae cell ultrastructure and infection structures of pathogenic and mycorrhizal fungi. Moreover, a concise appendix of methods conventionally used for the study of fungal ultrastructure is provided.

Highlights

Transmission electron microscopy (TEM) observations of filamentous fungi have been determinant for understanding their structure but, even more important, for revealing the mechanisms of apical growth
Thanks to TEM observations, it was possible to show that the cell walls of arbuscular mycorrhizal fungi undergo a conspicuous change in their organization during their life cycle: the spore wall is thick and layered with a highly fibrillar chitin, while the hyphal wall becomes progressively thinner during the intracellular phase, reaching a thin amorphous structure in the thinner arbuscular branches (Bonfante-Fasolo et al, 1990)
The region between extrahaustorial membrane (EHM) and fungal cell wall is called extrahaustorial matrix and at TEM appears as formed by amorphous material, usually scarcely electron-dense in early phase of haustorium development and later showing aggregations of granular or amorphous material, possibly secreted by the host and forming a sort of exchanging/filtering layer between the two organisms (Aist and Bushnell, 1981) (Figure 7a)

Summary

Introduction

Transmission electron microscopy (TEM) observations of filamentous fungi have been determinant for understanding their structure but, even more important, for revealing the mechanisms of apical growth. By this technique it was possible to have a deeper insight in fungal wall structure and in the mechanisms of apical growth, regarding the trafficking of the different macromolecules involved in hyphae elongation and in the role of the Spitzenkorper (Roberson et al, 2010).

Results

Conclusion