Nitric oxide signalling in the root is required for MYB72-dependent systemic resistance induced by Trichoderma volatiles in Arabidopsis.

Volatile compounds (VCs) of Trichoderma fungi trigger an induced systemic resistance (ISR) in Arabidopsis that is effective against a broad spectrum of pathogens. The root-specific transcription factor MYB72 is an early regulator of ISR and also controls the activation of iron deficiency responses. Nitric oxide (NO) is involved in the regulation of MYB72-dependent iron deficiency responses in Arabidopsis roots, but the role of NO in the regulation of MYB72 and ISR by Trichoderma VCs remains unexplored. Using in vitro bioassays, Trichoderma VCs were applied to Arabidopsis seedlings. Plant perception of Trichoderma VCs triggered a burst of NO in Arabidopsis roots. By suppressing this burst using a NO scavenger, we show the involvement of NO in Trichoderma VCs-mediated regulation of MYB72. Using a NO scavenger and the Arabidopsis lines myb72 and nia1nia2 in in planta bioassays, we demonstrate that NO-signalling is required in the roots for the activation of Trichoderma VCs-mediated ISR against the leaf pathogen Botrytis cinerea. Analysis of the defence-related genes PR1 and PDF1.2 point to the involvement of root NO in priming leaves for enhanced defence. Our results support a key role of root NO-signalling in the regulation of MYB72 during the activation of ISR by Trichoderma VCs.