Abstract
As members of the plant microbiota, arbuscular mycorrhizal fungi (AMF) may be effective in enhancing plant resilience to drought, one of the major limiting factors threatening crop productivity. AMF host their own microbiota and previous data demonstrated that endobacteria thriving in Gigaspora margarita modulate fungal antioxidant responses. Here, we used the G. margarita–Candidatus Glomeribacter gigasporarum system to test whether the tripartite interaction between tomato, G. margarita and its endobacteria may improve plant resilience to combined water/nutrient stress. Tomato plants were inoculated with spores containing endobacteria (B+) or not (B-), and exposed to combined water/nutrient stress. Plants traits, AM colonization and expression of AM marker genes were measured. Results showed that mycorrhizal frequency was low and no growth effect was observed. Under control conditions, B+ inoculated plants were more responsive to the symbiosis, as they showed an up-regulation of three AM marker genes involved in phosphate and lipids metabolism compared with B− inoculated or not-inoculated plants. When combined stress was imposed, the difference between fungal strains was still evident for one marker gene. These results indicate that the fungal endobacteria finely modulate plant metabolism, even in the absence of growth response.
Highlights
Microbial communities associated with plants—the plant microbiota—include beneficial microorganisms which potentially help their host to cope with biotic and abiotic stresses [1,2].A role in plant resilience to drought, one of the main current threats for crops, has been attributed to specific components of the root microbiota [2] such as plant growth-promoting bacteria [3,4] and arbuscular mycorrhizal fungi (AMF)
Tomato plants were inoculated with G. margarita spores containing endobacteria (B+) or cured spores without endobacteria (B−), while not-inoculated plants were used as non-mycorrhizal controls (NM)
All the plants were grown under normal growth conditions and under combined stress (CS) where a reduction of about 60% of water and nutrients supply was applied
Summary
A role in plant resilience to drought, one of the main current threats for crops, has been attributed to specific components of the root microbiota [2] such as plant growth-promoting bacteria [3,4] and arbuscular mycorrhizal fungi (AMF). AMF are able to efficiently extract water from soil through an extended extra-radical mycelium, to enhance plant stomatal conductance [14] and to induce the plant production of osmolytes. They induce the plant production of ROS-scavenging anti-oxidant compounds [15], reducing oxidative stress [16], Plants 2020, 9, 886; doi:10.3390/plants9070886 www.mdpi.com/journal/plants
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