triggers an early and transient burst of nitric oxide and the upregulation of in tomato roots.

We recently demonstrated that nitric oxide (NO) accumulation and transcriptional regulation are early components of the regulatory pathway that is activated in tomato roots during the onset of the mycorrhizal symbiosis between and tomato roots. We further showed that the mycorrhizal interaction was associated with a specific NO-related signature, different from that triggered by the pathogen . Here, we extend our investigation by exploring the NO- and related root responses elicited by another root mutualistic endosymbiotic fungus: T-78. By using T-78 -grown cultures, we found that T-78 triggered an early and transient burst of NO in tomato roots during the first hours after the interaction. T-78 also elicited the early upregulation of , which was maintained during the analyzed timespan. By using glass-house bioassays, we found that in a well-established tomato-T-78 symbiosis, NO root levels were maintained at basal level while expression remained upregulated. Our results demonstrate that the T-78 symbiosis is associated with a rapid and transient burst of NO in the host roots and the transcriptional activation of from early stages of the interaction until the establishment of the symbiosis, most likely to control NO levels and favor the mutualistic symbiosis.