Plant ability to cope with environmental stresses is essential for their survival. There is increasing evidence that rhizosphere microorganisms can impact the ecology, fitness, and shape of plant communities, conferring resistance to (a)biotic stresses. Indeed, the soil-plant interface is a very intricate and dynamic microenvironment where complex networks of multitrophic interactions take place and influence all plant functions. One promising and environmental-friendly approach to sustainably improve crop production and soil health is to harness the beneficial properties of microorganisms. Many beneficial microbes (BM) are already known and widely exploited as biostimulants to enhance plant growth and productivity, and to improve tolerance against a wide range of abiotic stressors. Nevertheless, a growing interest is addressed to the isolation of new BM. To this aim, extreme ecosystems could represent a valuable reservoir of microorganisms that evolved unique biochemical and physiological strategies to survive harsh environmental conditions. The main interest of this research unit is to isolate culturable fungi from plants and soil from extreme (i.e., Arctic and Antarctic) environments to test their potential as plant growth promoters on horticultural and crop plants. Their peculiar adaptive strategies in the native environment could also make them valuable tools for improving the resistance/resilience of crops to abiotic stresses. In addition, the disclosure of the functional role of mycoviruses or circular viroid-like RNAs in modulating fungal host biology and, consequentially, its effect on plant host is a new field of research that can open new perspective for the exploitation of beneficial mycovirus-fungus interactions as sustainable tools in agro-ecosystems. The study of the effect of isogenic virus-infected and virus-free fungal isolates on plant response to abiotic stress can help revealing the biological role of this tripartite interaction and its biotechnological application. Furthermore, improving knowledge on meta-interactions between plants and their hosts using -omics techniques will help overcome limitations that prevent the development of sustainable plant protection strategies and preserve and valorize beneficial microorganisms and the ecological services they provide. This research unit also aims to explore other potential applications of microorganisms from extreme environments whose specialization make them a potential source of novel natural products. To this aim fungal extract can be tested for the presence of extremozymes, extremolytes and secondary metabolites of high relevance for white, green, and red biotechnologies.