Early endocytosis as a key to understanding mechanisms of plasma membrane tension regulation in filamentous fungi

Role of cell membrane homeostasis in the pathogenicity of pathogenic filamentous fungi

The cell membrane forms a fundamental part of all living cells and participates in a variety of physiological processes, such as material exchange, stress response, cell recognition, signal transduction, cellular immunity, apoptosis, and pathogenicity. Here, we review the mechanisms and functions of the membrane structure (lipid components of the membrane and the biosynthesis of unsaturated fatty acids), membrane proteins (transmembrane proteins and proteins contributing to membrane curvature), transcriptional regulation, and cell wall components that influence the virulence and pathogenicity of filamentous fungi.

Generation of protoplasts provides a powerful experimental research tool for biological and pathogenicity studies of Pythium insidiosum

INTRODUCTION

Pythiosis is a high-mortality infectious condition in humans and animals. The etiologic agent is Pythium insidiosum. Patients present with an ocular, vascular, cutaneous/subcutaneous, or gastrointestinal infection. Antifungal medication often fails to fight against P. insidiosum. The effective treatment is limited to radical surgery, resulting in organ loss. Fatal outcomes are observed in advanced cases. Pythiosis needs to be studied to discover novel methods for disease control. Genome data of P. insidiosum is publicly available. However, information on P. insidiosum biology and pathogenicity is still limited due to the lack of a cost-effective animal model and molecular tools.

MATERIALS AND METHODS

We aimed to develop a high-efficiency protocol for generating P. insidiosum protoplast, and used it to set up an animal model, in vitro drug susceptibility assay, and DNA transformation for this pathogen.

RESULTS

P. insidiosum protoplast was successfully generated to establish a feasible pythiosis model in embryonic chicken eggs and an efficient in vitro drug susceptibility assay. DNA transformation is a critical method for gene manipulation necessary for functional genetic studies in pathogens. Attempts to establish a DNA transformation method for P. insidiosum using protoplast were partly successful. Significant work needs to be done for genetically engineering a more robust selection marker to generate stable transformants at increased efficiency.

CONCLUSION

This study is the first to report an efficient P. insidiosum protoplast production for clinical and research applications. Such advances are crucial to speeding up the pathogen's biology and pathogenicity exploration.

Lomasomes and Other Fungal Plasma Membrane Macroinvaginations Have a Tubular and Lamellar Genesis

The plasma membrane of filamentous fungi forms large-sized invaginations, which are either tubes or parietal vesicles. Vesicular macroinvaginations at the ultrastructural level correspond to classical lomasomes. There is an assumption that vesicular macroinvaginations/lomasomes may be involved in macrovesicular endocytosis. The original aim of this study was to test for the presence of macroendocytosis in xylotrophic basidiomycetes using time-lapse and Z-stacks fluorescent microscopic technologies. However, the results were unexpected since most of the membrane structures labeled by the endocytic tracer (FM4-64 analog) are various types of plasma membrane macroinvaginations and not any endomembranes. All of these macroinvaginations have a tubular or lamellar genesis. Moreover, under specific conditions of a microscopic preparation, the diameter of the tubes forming the macroinvaginations increases with the time of the sample observation. In addition, the morphology and successive formation of the macroinvaginations mimic the endocytic pathway; these invaginations can easily be mistaken for endocytic vesicles, endosomes, and vacuole-lysosomes. The paper analyzes the various macroinvagination types, suggests their biological functions, and discusses some features of fungal endocytosis. This study is a next step toward understanding complex fungal physiology and is a presentation of a new intracellular tubular system in wood-decaying fungi.

Both Clathrin-Mediated and Membrane Microdomain-Associated Endocytosis Contribute to the Cellular Adaptation to Hyperosmotic Stress in Arabidopsis

As sessile organisms, plants must directly deal with an often complex and adverse environment in which hyperosmotic stress is one of the most serious abiotic factors, challenging cellular physiology and integrity. The plasma membrane (PM) is the hydrophobic barrier between the inside and outside environments of cells and is considered a central compartment in cellular adaptation to diverse stress conditions through dynamic PM remodeling. Endocytosis is a powerful method for rapid remodeling of the PM. In animal cells, different endocytic pathways are activated in response to osmotic stress, while only a few reports are related to the endocytosis response pathway and involve a mechanism in plant cells upon hyperosmotic stress. In this study, using different endocytosis inhibitors, the microdomain-specific dye di-4-ANEPPDHQ, variable-angle total internal reflection fluorescence microscopy (VA-TIRFM), and confocal microscopy, we discovered that internalized Clathrin Light Chain-Green Fluorescent Protein (CLC-GFP) increased under hyperosmotic conditions, accompanied by decreased fluorescence intensity of CLC-GFP at the PM. CLC-GFP tended to have higher diffusion coefficients and a fraction of CLC-GFP molecules underwent slower diffusion upon hyperosmotic stress. Meanwhile, an increased motion range of CLC-GFP was found under hyperosmotic treatment compared with the control. In addition, the order of the PM decreased, but the order of the endosome increased when cells were in hyperosmotic conditions. Hence, our results demonstrated that clathrin-mediated endocytosis and membrane microdomain-associated endocytosis both participate in the adaptation to hyperosmotic stress. These findings will help to further understand the role and the regulatory mechanism involved in plant endocytosis in helping plants adapt to osmotic stress.

Evaluation of the carbonylation of filamentous fungi proteins by dry immune dot blotting

The development of mycological gerontology requires effective methods for assessing the biological age of fungal cells. This assessment is based on the analysis of a complex of aging and oxidative stress markers. One of the most powerful such markers is the protein carbonylation. In this study, the already known method of dry immune dot blotting is adapted for mycological studies of the content of protein carbonyl groups. After testing the method on a number of filamentous fungi species, some features of the accumulation of carbonylated proteins in mycelium were established. Among these features: (i) a weak effect of exogenous oxidative stress on the accumulation of carbonyls in a number of fungi, (ii) reversibility of the carbonyl accumulation, (iii) possibility of arbitrary regulation of carbonyl content by fungus itself and (iv) the influence of hormesis. In addition, two polar strategies for the accumulation of carbonyl modification were revealed, named Id-strategy (Indifferent) and Cn-strategy (Concern). Thus, even the analysis of one marker allows making some preliminary general assumptions and conclusions. For example, the idea that fungi can freely regulate their biological age is confirmed. This feature makes fungi very flexible in terms of responding to environmental influences and promising objects for gerontology.