Role of nitric oxide signalling in beneficial and pathogenic plant–fungal interactions

Resumen

The present Doctoral Thesis aims to determine the regulatory role of NO in the establishment of beneficial and pathogenic interactions of plants with soil fungi and to decipher its possible implication in the ISR against pathogenic fungi triggered in plants by Trichoderma volatile compounds. Altogether, in this PhD Thesis we have evidenced that NO harbours an important signalling role during plant–fungal interactions. We conclude that NO is a key signal in the establishment and fine–tuning of both mutualistic and pathogenic interactions, being its accumulation a common feature among them. However, the signature triggered differs quantitatively and in its spatio–temporal distribution in the different interactions. Indeed, this NO signature not only differs between a beneficial and a pathogenic fungus but also between different fungal mutualistic interactions. We further proved that these differences in NO signatures are concomitant with a differential transcriptional regulation of PHYTOGB1. This gene seems to exert a key role in controlling NO levels during the onset and in well–established beneficial interactions. Regarding pathogenic interplays, we have found that fungal pathogens might down–regulate PHYTOGB1, most likely to increase NO levels and promote favourable conditions for the invasion. Besides that, we further have confirmed that NO accumulation is triggered in Arabidopsis roots in response to Trichoderma volatile compounds. This accumulation is required for the upregulation of MYB72, that exerts a pivotal role in Trichoderma volatile compounds–mediated ISR response. Thus, NO signalling acts upstream of MYB72 and it is essential for triggering ISR.