Chemistry Research Unit, Center for Medical, Agricultural, and Veterinary Entomology, United States Department of Agriculture, Agricultural Research Service, Gainesville, FL, 32608, USA.
Section of Cell and Developmental Biology, University of California at San Diego, La Jolla, CA, 92093-0380, USA.
Planta. 2018 Apr;247(4):863-873. doi: 10.1007/s00425-017-2830-5.
Chemical isolation and NMR-based structure elucidation revealed a novel keto-acidic sesquiterpenoid, termed zealexin A4 (ZA4). ZA4 is elicited by pathogens and herbivory, but attenuated by heightened levels of CO . The identification of the labdane-related diterpenoids, termed kauralexins and acidic sesquiterpenoids, termed zealexins, demonstrated the existence of at least ten novel stress-inducible maize metabolites with diverse antimicrobial activity. Despite these advances, the identity of co-occurring and predictably related analytes remains largely unexplored. In the current effort, we identify and characterize the first sesquiterpene keto acid derivative of β-macrocarpene, named zealexin A4 (ZA4). Evaluation of diverse maize inbreds revealed that ZA4 is commonly produced in maize scutella during the first 14 days of seedling development; however, ZA4 production in the scutella was markedly reduced in seedlings grown in sterile soil. Elevated ZA4 production was observed in response to inoculation with adventitious fungal pathogens, such as Aspergillus flavus and Rhizopus microsporus, and a positive relationship between ZA4 production and expression of the predicted zealexin biosynthetic genes, terpene synthases 6 and 11 (Tps6 and Tps11), was observed. ZA4 exhibited significant antimicrobial activity against the mycotoxigenic pathogen A. flavus; however, ZA4 activity against R. microsporus was minimal, suggesting the potential of some fungi to detoxify ZA4. Significant induction of ZA4 production was also observed in response to infestation with the stem tunneling herbivore Ostrinia nubilalis. Examination of the interactive effects of elevated CO (E-CO) on both fungal and herbivore-elicited ZA4 production revealed significantly reduced levels of inducible ZA4 accumulation, consistent with a negative role for E-CO on ZA4 production. Collectively, these results describe a novel β-macrocarpene-derived antifungal defense in maize and expand the established diversity of zealexins that are differentially regulated in response to biotic/abiotic stress.
化学分离和基于 NMR 的结构阐明揭示了一种新型的酮酸性倍半萜，称为 zealexin A4（ZA4）。ZA4 由病原体和草食性诱发，但被升高的 CO 水平减弱。对被称为 kauralexins 的 labdane 相关二萜和被称为 zealexins 的酸性倍半萜的鉴定表明，至少有十种具有不同抗菌活性的新型应激诱导的玉米代谢物存在。尽管取得了这些进展，但共存和可预测相关分析物的身份在很大程度上仍未得到探索。在当前的研究中，我们鉴定并表征了 β-大牻牛儿烯的第一个倍半萜酮酸衍生物，命名为 zealexin A4（ZA4）。对不同玉米自交系的评估表明，ZA4 在幼苗发育的前 14 天普遍存在于玉米盾片中；然而，在无菌土壤中生长的幼苗中，ZA4 在盾片中的产生明显减少。在接种不定真菌病原体如黄曲霉和根霉微菌时，观察到 ZA4 的产生增加，并且观察到 ZA4 产生与预测的 zealexin 生物合成基因，萜烯合酶 6 和 11（Tps6 和 Tps11）的表达之间存在正相关关系。ZA4 对产霉菌毒素的病原体黄曲霉具有显著的抗菌活性；然而，ZA4 对根霉微菌的活性最小，表明一些真菌有解毒 ZA4 的潜力。在受到茎隧道食草昆虫玉米穗虫的侵害时，也观察到 ZA4 产生的显著诱导。对升高的 CO（E-CO）对真菌和草食性诱发的 ZA4 产生的相互作用的研究表明，可诱导的 ZA4 积累水平显著降低，这与 E-CO 对 ZA4 产生的负作用一致。总的来说，这些结果描述了玉米中一种新型的β-大牻牛儿烯衍生的抗真菌防御，并扩展了已建立的 zealexin 多样性，这些 zealexin 是对生物/非生物胁迫的差异调节。
