AUTHOR=Wang Shi , Park Yong-Soon , Yang Yang , Borrego Eli J. , Isakeit Tom , Gao Xiquan , Kolomiets Michael V. 

TITLE=Seed-Derived Ethylene Facilitates Colonization but Not Aflatoxin Production by Aspergillus flavus in Maize

JOURNAL=Frontiers in Plant Science

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2017.00415

DOI=10.3389/fpls.2017.00415

ISSN=1664-462X

ABSTRACT=<p>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 <italic>in vitro</italic> fungal cultures exposed to ET suggested that exogenous ET may regulate the production of aflatoxin by <italic>Aspergilli</italic>. However, the function of endogenous, seed-derived ET has not been explored. In this study, we found that the maize lipoxygenase <italic>lox3</italic> mutant, previously reported to be susceptible to <italic>Aspergillus</italic> spp., emitted greater levels of ET upon <italic>A. flavus</italic> infection, suggesting the potential involvement of endogenous ET in the susceptibility of maize to <italic>A. flavus</italic>. Supporting this idea, both colonization and conidiation of <italic>A. flavus</italic> were reduced in wild-type (WT) kernels treated with AgNO<sub>3</sub>, an ET synthesis inhibitor. There was no ET emission from non-viable kernels colonized by <italic>A. flavus</italic>, suggesting that living seed but not the fungus itself was the primary source of ET released upon infection with <italic>A. flavus</italic>. The kernels of <italic>acs2</italic> and <italic>acs6</italic>, two ET biosynthetic mutants carrying <italic>Mutator</italic> transposons in the ACC synthase genes, <italic>ACS2</italic> and <italic>ACS6</italic>, respectively, displayed enhanced seed colonization and conidiation, but not the levels of aflatoxin, upon infection with <italic>A. flavus</italic>. Surprisingly, both <italic>acs2</italic> and <italic>acs6</italic> mutant kernels emitted greater levels of ET in response to infection by <italic>A. flavus</italic> 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 <italic>A. flavus</italic> infection. Collectively, these findings suggested that ET emitted by infected seed facilitates colonization by <italic>A. flavus</italic> but not aflatoxin production.</p>