Nitric oxide in plant-fungal interactions

Whilst many interactions with fungi are detrimental for plants, others are beneficial and result in improved growth and stress tolerance. Thus, plants have evolved sophisticated mechanisms to restrict pathogenic interactions while promoting mutualistic relationships. Numerous studies have demonstrated the importance of nitric oxide (NO) in the regulation of plant defence against fungal pathogens. NO triggers a reprograming of defence-related gene expression, the production of secondary metabolites with antimicrobial properties, and the hypersensitive response. More recent studies have shown a regulatory role of NO during the establishment of plant-fungal mutualistic associations from the early stages of the interaction. Indeed, NO has been recently shown to be produced by the plant after the recognition of root fungal symbionts, and to be required for the optimal control of mycorrhizal symbiosis. Although studies dealing with the function of NO in plant-fungal mutualistic associations are still scarce, experimental data indicate that different regulation patterns and functions for NO exist between plant interactions with pathogenic and mutualistic fungi. Here, we review recent progress in determining the functions of NO in plant-fungal interactions, and try to identify common and differential patterns related to pathogenic and mutualistic associations, and their impacts on plant health.We apologize to any colleagues whose studies have not been cited due to space limitations. This research was supported by grants EX12-BIO296 (from the Junta de Andalucía), and PGC2018-098372 and RTI2018-094350-B-C31 (from the Spanish Ministry of Science, Innovation and University). LP-A and LT-C were supported by University Staff Training (FPU) fellowships from the Spanish Ministry of Education, Culture and Sports. AMM further acknowledges funding from the program for attracting talent to Salamanca from the Fundación Salamanca Ciudad de Cultura y Saberes.Peer Reviewe