Analysis of M82 tomato inoculated with Gigaspora margarita containing or not endobacteria under combined drought

In this experiment we tested if the tripartite interaction between tomato, AMF and endobacteria they host is able to improve plant resilience to water/nutrient stress. To this aim we used the Gigaspora margarita-CaGg (Candidatus Glomeribacter gigasporarum) biological system. Tomato M82 plants were inoculated with G. margarita spores containing its endobacterium (B+), cured spores without endobacterium (B-) or not inoculated (control) and grown under combined stress or not. Mycorrhizal colonization and plant traits were measured considering two time points, 60 days and 90 days after the experiment start. At the last sampling plant WUE/NUE and expression profiles of AM marker genes were measured. Results showed that Gigaspora is not a good symbiont for tomato since mycorrhizal frequency was rather low. Plant growth was not influenced by presence/absence of endobacteria while moderate water stress had the strongest impact. Interestingly we found that, irrespective of combined stress, B+ inoculated plants were more responsive to the AM symbiosis since they showed a higher activation of the 3 AM marker genes compared to the B- or not inoculated plants. These results indicate that the presence/absence of endobacteria could finely modulate plant metabolism at molecular level although a clear growth response was not detected.