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Boosting plant defence by Arbuscular Mycorrhizal fungi: Induced Resistance and signalling pathways involved

Final Activity Report Summary - AMIR (Boosting plant defence by Arbuscular Mycorrhizal fungi: Induced Resistance and signalling pathways involved)

Root colonisation by arbuscular mycorrhizal (AM) fungi can improve plant resistance/tolerance to biotic stresses. Although this bioprotection has been observed in different plant systems, the underlying mechanisms remain largely unknown. In contrast to other types of induced resistance, a direct activation of defence related mechanisms has not been observed. Instead, mycorrhizal plants showed an enhanced capacity to activate defence responses, a phenomenon known as priming. Thus, establishment of mycorrhizal symbiosis seems to boost plant immunity.

To investigate the mechanisms and signalling pathways involved in bioprotection by AM fungi, we compared the response of non mycorrhizal and mycorrhizal tomato plants to different defence related signals. Gene expression was monitored in a time course experiment after shoot treatment with the defence related signalling molecules jasmonic (JA), salicylic (SA) acids or ethylene.

In mycorrhizal plants a differential regulation of the defence responses triggered was observed. Remarkably, upon JA treatment, shoots of mycorrhizal plants showed up to 10 times higher expression levels of some defence-related genes.

We confirmed that this primed response occurs also during interaction with pathogens. A genomic approach has been followed to determine the magnitude of the primed response.

In summary, our results evidence differential regulation of defence responses in mycorrhizal plants and point to a prominent role of priming for JA dependent responses in AM-induced resistance. The research constitutes a step forward in our knowledge of plant defence mechanisms and the development of safe, environmentally-friendly and durable strategies for crop protection.