|HUFFAKER, ALISA - University Of California
|SIMS, JAMES - Eth Zurich
|MYLROIE, ERIK - Bennett Aerospace
|SCHMELZ, ERICK - University Of California
Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2017
Publication Date: 12/19/2017
Citation: Christensen, S.A., Huffaker, A., Sims, J., Hunter III, C.T., Block, A.K., Vaughan, M.M., Willett, D.S., Mylroie, E., Williams, P.C., Schmelz, E.A. 2017. Fungal and herbivore elicitation of a newly identified maize sesquiterpenoid, zealexin A4, is constrained by abiotic stress. Planta. 247(4):863-873. https://doi.org/10.1007/s00425-017-2830-5.
Interpretive Summary: Corn production losses due to biotic (i.e. insect damage or microbe contamination) and abiotic stress (i.e. excess heat, drought, or carbon dioxide) result in billions of dollars in lost revenue annually. Despite these great economic losses, little is known about how corn plants can defend themselves against these threats. Scientists at the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, FL have identified a means by which corn plants defend themselves against fungal pathogens by discovering a new antibiotic molecule, termed zealexin A4 (ZA4). The accumulation of ZA4 is produced by the plant in response to fungal contamination to kill the fungus. Interestingly, the production of ZA4 in response to these biotic stress factors is reduced when treatments are conducted in the presence of elevated carbon dioxide. Collectively, these findings help researchers understand the underlying biology behind how maize adjusts to biotic and abiotic challenges. Future elucidation of the specific genes involved in the biosynthesis of ZA4 may contribute to molecular breeding practices that will make corn plants more resistant to biotic and abiotic stress, thus alleviating large economic losses that corn growers experience as a result of these threats.
Technical Abstract: The existence of microbe- or abiotic stress-inducible antimicrobials, termed phytoalexins, has only recently been discovered in maize. Identification and structural elucidation of the labdane-related diterpenoid kauralexins and sesquiterpenoid zealexins has collectively resulted in 10 novel pathogen-inducible molecules with varying antimicrobial activity. Despite these advances, many analytes that chromatograph in proximity to known phytoalexins remain unexplored. In this study, we identified and characterized one of the unknown analytes to be an acidic sesquiterpenoid derivative of ß-macrocarpene, designated as zealexin A4 (ZA4). Evaluation of diverse inbreds revealed that ZA4 is universally produced in maize scutella during the first 14 d of seedling development. Analysis of ZA4 production and Tps6/11 transcript accumulation in fungal-infected tissues demonstrated a positive relationship between the pathogen-inducible ZA4 and known zealexin biosynthesis genes. Examination of biotically stressed tissues treated with a variety of maize pathogens or the stem tunneling herbivore Ostrinia nubilalis showed elicitation of ZA4 in an organism-specific manner. Investigation of the abiotic stress effects of elevated CO2 on fungal and herbivore-induced ZA4 production revealed significantly reduced elicitation, suggesting the negative impact of high CO2 on ZA4-mediated defenses. Characteristic of maize phytoalexins, ZA4 exhibited significant antimicrobial activity against the mycotoxigenic pathogen Aspergillus flavus. Collectively, these results highlight a novel ß-macrocarpene derived phytoalexin that is differentially regulated by biotic and abiotic stress.