Seed-Derived Ethylene Facilitates Colonization but Not Aflatoxin Production by in Maize.

Ethylene (ET) emitted by plant tissues has been broadly reported to play important roles in plant development, response to environmental stresses and defense against certain pathogens. Recent evidence obtained from using fungal cultures exposed to ET suggested that exogenous ET may regulate the production of aflatoxin by . However, the function of endogenous, seed-derived ET has not been explored. In this study, we found that the maize lipoxygenase mutant, previously reported to be susceptible to spp., emitted greater levels of ET upon infection, suggesting the potential involvement of endogenous ET in the susceptibility of maize to . Supporting this idea, both colonization and conidiation of were reduced in wild-type (WT) kernels treated with AgNO, an ET synthesis inhibitor. There was no ET emission from non-viable kernels colonized by , suggesting that living seed but not the fungus itself was the primary source of ET released upon infection with . The kernels of and , two ET biosynthetic mutants carrying transposons in the ACC synthase genes, and , respectively, displayed enhanced seed colonization and conidiation, but not the levels of aflatoxin, upon infection with . Surprisingly, both and mutant kernels emitted greater levels of ET in response to infection by as compared with WT seed. The increased ET in single mutants was found to be due to overexpression of functional ACS genes in response to infection. Collectively, these findings suggested that ET emitted by infected seed facilitates colonization by but not aflatoxin production.