Jasmonic acid signalling mediates resistance of the wild tobacco N icotiana attenuata to its native F usarium , but not A lternaria , fungal pathogens

We recently characterized a highly dynamic fungal disease outbreak in native populations of N icotiana attenuata in the southwestern U nited S tates. Here, we explore how phytohormone signalling contributes to the observed disease dynamics. Single inoculation with three native F usarium and A lternaria fungal pathogens, isolated from diseased plants growing in native populations, resulted in disease symptoms characteristic for each pathogen species. While A lternaria sp.‐infected plants displayed fewer symptoms and recovered, F usarium spp.‐infected plants became chlorotic and frequently spontaneously wilted. Jasmonic acid ( JA ) and salicylic acid ( SA ) levels were differentially induced after F usarium or A lternaria infection. Transgenic N . attenuata lines silenced in JA production or JA conjugation to isoleucine ( JA ‐ Ile ), but not in JA perception, were highly susceptible to infection by F . brachygibbosum   U tah 4, indicating that products derived from the JA ‐ Ile biosynthetic pathway, but not their perception, is associated with increased F usarium resistance. Infection assays using ov ‐ nahG plants which were silenced in pathogen‐induced SA accumulations revealed that SA may increase N . attenuata's resistance to F usarium infection but not to A lternaria . Taken together, we propose that the dynamics of fungal disease symptoms among plants in native populations may be explained by a complex interplay of phytohormone responses to attack by multiple pathogens.