The role of iodine in plant defence against Botrytis cinerea

• Iodine nutrition (micromolar amounts) boosts plant defence against Botrytis cinerea ;. • Iodine affects the production of salycilic acid, jasmonic acid, ethylene and H 2 O 2 ;. • Iodine affects the expression of several pathogenesis-related (PR) genes;. • Jasmonic acid play a preferential role in the iodine-induced resistance to B. cinerea . • Iodine was hypothesized to be effective against a broad spectrum of pathogens. Iodine has been recently defined as a plant nutrient, triggering beneficial outcomes in terms of plant fitness and crop quality. In the present study, we demonstrated that iodine boosts Arabidopsis tolerance against the necrotrophic fungal pathogen Botrytis cinerea. At micromolar concentrations, we found that iodine activated a broad spectrum of immune-like responses, stimulating the transient accumulation of H 2 O 2 , likely acting as a second messenger. Iodine activated three major hormonal players involved in plant defence, namely, salicylic acid, jasmonic acid and ethylene. Several pathogenesis-related (PR) genes, particularly PR2 and PR5 , were also strongly induced by iodine. The use of Arabidopsis mutants impaired in SA, JA or ET biosynthesis/signalling allowed us to demonstrate the central role of JA in the iodine-induced resistance to B. cinerea. Nevertheless, the wide range of defence-like responses triggered by iodine suggests its potential effectiveness against a broad spectrum of biotic agents. Integrating iodine in plant nutritional programs thus represents a promising, eco-friendly, and easy-to-apply tool to fight against pathogen attacks, which could be alternative/additional to using traditional pesticides.