Plants harbor a large diversity of endophytic microbes. Meadow fescue (Festuca pratensis) is a cool-season grass known for its symbiotic relationship to the systemic and vertically- via seeds - transmitted fungal endophyte Epichloë uncinata but the effect of the endophyte on the microbial endophyte community and phytohormones is largely unexplored. Here, we sequenced the endophytic bacterial and fungal communities in the leaves and roots, analyzed phytohormone concentrations and plant performance parameters in Epichloë-symbiotic (E+) and Epichloë-free (E-) individuals of two meadow fescue cultivars. The endophytic leaf microbial community differed between leaf and root tissues independent of endophyte symbiosis while the fungal community was different in leaves of Epichloë-symbiotic and Epichloë-free plants in both cultivars. At the same time, endophyte symbiosis decreased salicylic acid and increased auxin concentrations in leaves. Epichloë-symbiotic plants showed a higher biomass, chlorophyll content (SPAD) and higher seed mass at the end of the season. Our results demonstrate that Epichloë-symbiosis alters the leaf fungal microbiome, which coincides with changes in phytohormone concentrations, indicating that Epichloë endophytes affect both, plant immune responses and other fungal endophytes. Whether the effect of Epichloë endophytes on other fungal endophytes is connected to changes in the phytohormone concentrations remains to be elucidated.

Brassinosteroids (BR) are key phytohormones involved in the regulation of major processes of cell metabolism guiding plant growth. In the past decades, new evidence made it clear that BRs also play a key role in the orchestration of plant responses to many abiotic and biotic stresses. In the present work we analyzed the impact of foliar treatment with 24-epicastasterone (ECS) on the endogenous content of major phytohormones (auxins, salicylic acid, jasmonic acid, abscisic acid) and their intermediates in soybean leaves 7 days following the treatment. Changes in the endogenous content of phytohormones have been identified and quantified by LC/MS. Obtained results point to a clear role of ECS in the upregulation of auxin content (indole-3-acetic acid, IAA) and downregulation of salicylic, jasmonic, and abscisic acid levels. These data confirm that under optimal conditions ECS in tested concentrations of 0,25 µM and 1 µM might promote growth in soybean by inducing auxin contents. Benzoic acid (a precursor of salicylic acid (SA)), but not SA itself, has also been highly accumulated under ECS treatment which indicates an activation of the adaption strategies of cell metabolism to possible environmental challenges.