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29 páginas, 6 figuras, 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., This research was supported by the grants OTR04036 from Fundación Salamanca Ciudad de Cultura y Saberes and Ayuntamiento de Salamanca; P12BIO296 from Junta de Andalucía; RTI2018-094350-B-C31 and GC2018-098372-B-100 from the Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund (MCIU/AEI/ERDF); and Marie Skłodowska-Curie Intra-European Fellowship FP7-PEOPLE-2011-IEF no. 301662 (to AMM). AMM and LP acknowledge the support of the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig funded by the German Research Foundation (FZT 118). LP further acknowledges to the PhD International Mobility Programme from University of Granada.

In Arabidopsis (Arabidopsis thaliana), the plastidial isoform of phosphoglucose isomerase (PGI1) mediates photosynthesis, metabolism, and development, probably due to its involvement in the synthesis of isoprenoid-derived signals in vascular tissues. Microbial volatile compounds (VCs) with molecular masses of, This work was supported by the Ministerio de Ciencia e Innovación (MCIN) and Agencia Estatal de Investigación (AEI)/10.13039/501100011033/ (grants BIO2016-78747-P, PID2019-104685GB-100 and PID2019-107657RB-C22) and the Ministry of Education, Youth and Sport of the Czech Republic and the European Regional Development Fund (ERDF) project entitled “Plants as a tool for sustainable global development” (No. CZ.02.1.01/0.0/0.0/16_019/0000827).