The Role of Strigolactone in the Cross-Talk Between and the Endophytic Fungus sp.

Over the last years the role of fungal endophytes in plant biology has been extensively studied. A number of species were shown to positively affect plant growth and fitness, thus attempts have been made to utilize these microorganisms in agriculture and phytoremediation. Plant-fungi symbiosis requires multiple metabolic adjustments of both of the interacting organisms. The mechanisms of these adaptations are mostly unknown, however, plant hormones seem to play a central role in this process. The plant hormone strigolactone (SL) was previously shown to activate hyphae branching of mycorrhizal fungi and to negatively affect pathogenic fungi growth. Its role in the plant-endophytic fungi interaction is unknown. The effect of the synthetic SL analog GR24 on the endophytic fungi sp. growth, respiration, HO production and the activity of antioxidant enzymes was evaluated. We found fungi colony growth rate was decreased in a GR24 concentration dependent manner. Additionally, the fungi accumulated more HO what was accompanied by an altered activity of antioxidant enzymes. Symbiosis with sp. positively affected growth, but SL was necessary for the establishment of the beneficial interaction. biosynthesis mutants and , but not the SL signaling mutant did not develop the beneficial phenotype. The negative growth response was correlated with alterations in SA homeostasis and a significant upregulation of genes encoding selected plant defensins. The fungi were also shown to be able to decompose SL and to downregulate the expression of SL biosynthesis genes. Additionally, we have shown that GR24 treatment with a dose of 1 μM activates the production of SA in . The results presented here provide evidence for a role of SL in the plant-endophyte cross-talk during the mutualistic interaction between and sp.