Genetic elucidation of interconnected antibiotic pathways mediating maize innate immunity

Authors: DING, YEZHANG - University Of California, San Diego; WECKWERTH, PHILLIP - University Of California, San Diego; PORETSKY, ELLY - University Of California, San Diego; MURPHY, KATHERINE - University Of California, San Diego; SIMS, JAMES - Eth Zurich; SALDIVAR, EVAN - University Of California, San Diego; Christensen, Shawn; CHAR, SI NIAN - University Of Missouri; YANG, BING - University Of Missouri; TONG, ANH-DAO - University Of California, San Diego; SHEN, ZHOUXIN - University Of California, San Diego; KREMLING, KARL - Cornell University; Buckler, Edward - Ed; KONO, TOM - University Of Minnesota; NELSON, DAVID - University Of Tennessee; BOHLMANN, JORG - University Of British Columbia; Bakker, Matthew; Vaughan, Martha; KHALIL, AHMED - University Of California, San Diego; BETSIASHVILI, MARIAM - University Of California, San Diego; BRIGGS, STEVEN - University Of California, San Diego; ZERBE, PHILIPP - University Of California, San Diego; SCHMELZ, ERIC - University Of California, San Diego; HUFFAKER, ALISA - University Of California, San Diego

Submitted to: Nature Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/11/2020
Publication Date: 10/26/2020
Citation: Ding, Y., Weckwerth, P.R., Poretsky, E., Murphy, K.M., Sims, J., Saldivar, E., Christensen, S.A., Char, S., Yang, B., Tong, A., Shen, Z., Kremling, K.A., Buckler IV, E.S., Kono, T., Nelson, D.R., Bohlmann, J., Bakker, M.G., Vaughan, M.M., Khalil, A.S., Betsiashvili, M., Briggs, S.P., Zerbe, P., Schmelz, E.A., Huffaker, A. 2020. Genetic elucidation of interconnected antibiotic pathways mediating maize innate immunity. Nature Plants. (6):1375-1388. https://doi.org/10.1038/s41477-020-00787-9.
DOI: https://doi.org/10.1038/s41477-020-00787-9

Interpretive Summary: It’s known that crops produce specialized molecules to defend against diseases and pathogens; however, due to difficulty in piecing together the pathways that result in the production and utilization of the molecules, we are unable to properly discern their function. Obtaining a detailed and accurate blueprint of the pathways is crucial for any effort to synthetically improve the effectiveness and efficiency of the pathways. Terpenoids are a class of molecules that largely contribute to a plant's ability to fight off pathogens and zealexins are the largest class of defensive terpenoids in corn. Through the integration of methods from various fields of biology, ten genes existing in three clusters were identified to interact to produce a diverse set of defensive zealexins. Redundancy of zealexin pathway genes ensures the production of zealexins even if one copy of a gene is non-functional. The new understanding of the zealexin pathway interactions opens it up for consideration in breeding and synthetic pathway improvements through genetic engineering.

Technical Abstract: Specialized metabolites constitute key layers of immunity that underlie disease resistance in crops; however, challenges in resolving pathways limit our understanding of the functions and applications of these metabolites. In maize (Zea mays), the inducible accumulation of acidic terpenoids is increasingly considered to be a defense mechanism that contributes to disease resistance. Here, to understand maize antibiotic biosynthesis, we integrated association mapping, pan-genome multi-omics correlations, enzyme structure–function studies and targeted mutagenesis. We define ten genes in three zealexin (Zx) gene clusters that encode four sesquiterpene synthases and six cytochrome P450 proteins that collectively drive the production of diverse antibiotic cocktails. Quadruple mutants in which the ability to produce zealexins (ZXs) is blocked exhibit a broad-spectrum loss of disease resistance. Genetic redundancies ensuring pathway resiliency to single null mutations are combined with enzyme substrate promiscuity, creating a biosynthetic hourglass pathway that uses diverse substrates and in vivo combinatorial chemistry to yield complex antibiotic blends. The elucidated genetic basis of biochemical phenotypes that underlie disease resistance demonstrates a predominant maize defense pathway and informs innovative strategies for transferring chemical immunity between crops.