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Discovery of novel root specific maize dolabralexin defenses: an expanding family of antibiotics


As the world’s largest annually harvested crop, optimization of maize (Zea mays) protective biochemical defenses that impede pest and pathogen attack will be essential to mitigate significant yield losses that could compromise our global food security. To better understand the diversity of pathogen elicited maize antibiotics, we leveraged a rapid sample preparation technique termed Vapour Phase Extraction (VPE) coupled with mass spectrometry (MS), high-performance liquid chromatography (HPLC) and Nuclear Magnetic Resonance (NMR) spectroscopy. We focused experiments on roots of field-grown maize lines discovered to produce high levels of terpenoid defenses. Leveraging the power of VPE, HPLC, and NMR, we found a series of novel modified dolabradiene derivatives, predictably part of the dolabralexin diterpenoid family of maize defenses. To generate endogenous evidence that the novel dolabralexins are products of diterpene synthases Anther ear 2 (ZmAn2) and Kaurene Synthase-Like 4 (ZmKSL4), we analyzed Zman2 and Zmksl4 mutants and demonstrated an absence of all dolabralexin-related metabolites. Chemical analyses of maize Biparental Recombinant Inbred Line (RIL) mapping population and an association panel coupled with global gene co-expression analyses using Mutual Ranks and Agrobacterium-mediated transient overexpression enzyme assays in Nicotiana benthamiana using different combinations of ZmAn2 and ZmKSL4 with cytochrome (CYP) P450 monooxygenases have revealed that ZmCYP71Z16 may contribute to the production of complex dolabralexin products.

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