Nitric oxide signalling controlling fungal reproduction

Fungal asexual reproduction results in the formation of highly volatile propagules (conidia). These conidia are the infectuos particles in the case of pathogens, such as the most prevalent airborn pathogenic fungi Aspergillus. Filamentous fungi (e.g. Aspergillus) initiate developmental programs (conidiation, sexual development, ...) upon the detection of specific environmental signals. For decades, some of these environmental signals have been known. However, the knowledge of how those signals are detected, and how the information is transmitted and then integrated to activate the developmental programmes is still very scarce. Development is controlled by a very complex network of regulators responding to those inducing conditions. Only the study of the light signal has been approached in some detail to date. Previous work through a transnational collaboration between the Groups of Prof. J. Strauss (BOKU, Austria) and Dr. D. Cnovas (Univ. Sevilla, Spain) unveiled that nitric oxide (NO) is a novel signal in fungi regulating development by cross-regulation with the light signal. The main objective of this proposal is to study the connection and crosstalk between these two signals (NO and light) inducing development and controlling the balance between two developmental programmes in fungi, using Aspergillus nidulans as a model system. We plan (1) to identify an alleged but so far unknown NO synthase in fungi, (2) to identify the signalling cascade at the molecular level for NO control, using development undertaken by NO, an emerging signal in fungi, and (2) to understand the connection between light and NO. The study of fungal reproduction, the mode of dispersion that allows colonization of new niches, has a strong impact on: human health by reducing fungal pathogens conidiation and consequently, the risks of virulent spores inhaling; and in biotechnology by increasing conidiation in industrially important strains, which often conidiate poorly. The collaboration between the host Group in BOKU and the applicant is fundamental for the success of this project. The BOKU group has a strong expertise in the regulation of N metabolism, which is partially controlling the intracellular levels of NO. The applicant is specialized in fungal development and by light.

Nitric oxide (NO) is an important signalling molecule in all organisms and has been extensively studied in mammals, allowing to save many humans lives through the regulation of vasodilation in cases of acute stroke. However, the study of NO has only been approached in fungi recently and it is still in its infancy. During this project we have developed a new platform that allows to grow fungi in a format that resemble fungal growth in nature. Using this system we were able to unveil one of the routes for the synthesis of NO in fungi for the first time, involving the oxidation of nitrite to NO by the nitrate reductase. A second route was also identified that uses arginine as a substrate and it is regulated by controlling the subcellular localization of arginine intracellular pools. There is an intricated feedback regulation between the NO levels and the induction of the morphogenetic programs controlling fungal development and reproduction. This project has also allowed to begin the search for alternative routes of NO synthesis in fungi, which is currently undergoing as well as the characterization of the regulatory role of NO in the biology of the fungal cells.