Drought resistance of Ectomycorrhizal fungi in the Suillus genus

Sammanfattning: Rising instances of drought are causing more tree seedling fatalities post-nursery outplanting. In the face of climate change, fostering resilient forestry practices is imperative for preserving the health and functionality of our forests. Ectomycorrhizal fungi (ECM), crucial for the drought resistance of key Swedish trees like pine and spruce, play a significant role in forest resilience. With the hypothesis that ECM species with a higher innate drought resistance can more effectively aid their tree symbionts in conditions of drought, it becomes interesting to investigate how drought influences the ECM mycobiont. Differential expressions of specialised water channel proteins called aquaporins (AQPs) have been found under conditions of drought, suggesting an integral role in the drought resilience of ECMs themselves, as well as in the mycorrhizal partnership. This master project aimed to deepen the understanding of drought resistance in the ectomycorrhizal Suillus genus. The characteristics of the gene repertoire of aquaporins within the Suillus genus were explored and drought effects on the growth patterns of three fungal species, S. variegatus, S. luteus and S. bovinus, were investigated. Fungal growth was studied under drought as simulated on Petri dishes by incorporating polyethylene glycol into the agar medium. Only a single isolate, being S. variegatus LV-1, showed a significant decrease in diameter and weight when subjected to drought compared to control conditions without PEG. Increased pigmentation and hyphal density were observed across all isolates growing in drought conditions, leading to the conclusion that although drought was achieved, the stress of the mycelium was not generally expressed in terms of diameter of growth or weight. Furthermore, a phylogenetic analysis of AQPs was carried out using the programs MAFFT and FigTree and key amino-acid motifs (i.e. NPA) that influence AQP substrate specificity as well as the topology of Suillus AQPs was analysed. Motifs and protein topology in the Suillus genus were generally consistent with the literature on fungal AQPs, with a few interesting divergences regarding the NPA motif. The thesis study resulted in the design of primers and validation of stable reference genes for future qPCR analysis of AQPs in S. variegatus.