Duplication and divergence of primary pathway genes underlie the evolution of plant specialized metabolism; however, mechanisms partitioning parallel hormone and defence pathways are often speculative. For example, the primary pathway intermediate ent-kaurene is essential for gibberellin biosynthesis and is also a proposed precursor for maize antibiotics. By integrating transcriptional coregulation patterns, genome-wide association studies, combinatorial enzyme assays, proteomics and targeted mutant analyses, we show that maize kauralexin biosynthesis proceeds via the positional isomer ent-isokaurene formed by a diterpene synthase pair recruited from gibberellin metabolism. The oxygenation and subsequent desaturation of ent-isokaurene by three promiscuous cytochrome P450s and a new steroid 5α reductase indirectly yields predominant ent-kaurene-associated antibiotics required for Fusarium stalk rot resistance. The divergence and differential expression of pathway branches derived from multiple duplicated hormone-metabolic genes minimizes dysregulation of primary metabolism via the circuitous biosynthesis of ent-kaurene-related antibiotics without the production of growth hormone precursors during defence.
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We thank A. Steinbrenner, P. Weckwerth, K. Dressano, J. Chan, K. O’Leary, M. Broemmer, H. Riggleman, S. Reyes, S. Delgado and J. Tran for help in planting, treatments and sampling (UCSD). Thanks also to L. Smith (UCSD) for shared UCSD Biology Field Station management. This work was supported by a grant from the National Science Foundation Plant-Biotic Interactions Program (grant no. 1758976 to E.S. and P.Z.), by a Department of Energy Joint Genome Institute Community Science Program grant (no. CSP2568 to P.Z., E.S. and A.H.) and by a fellowship provided by the National Science Foundation Graduate Research Fellowship Program (to K.M.M.).
The authors declare no competing interests.
Peer Review Information: Nature Plants thanks Hugues Renault and other, anonymous, reviewers for their contribution to the peer review of this work.
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Supplementary Figs. 1–22 and Supplementary Table 6.
Southern leaf blight (SLB; Cochliobolous heterostrophus) induced gene expression in maize leaves.
Summary of SLB-induced expression levels of diterpene synthases and related pathway genes in maize leaves.
Summary of SLB-induced expression levels of the maize cytochrome P450 gene family.
Co-expression analyses of ZmKSL2 with maize P450 gene family and all maize genes.
GWAS mapping interval identified using the ratio of highly oxidized kauralexins to total kauralexins.
Using the ratio of kauralexin A-/B-series metabolites as a trait, GWAS identifies an interval containing steriod 5a reductase candidates.
Protein fold changes of DiTPS pathway enzymes in the stem tissues (Zea mays var. W22) elicited with heat-killed Fusarium venenatum.
Maize mapping lines used for replicated genome wide association studies (GWAS) in the Goodman diversity panel and quantitative trait loci mapping in the nested association mapping subpopulation B73 × M162W.
Primers used for qrtPCR analysis.
Primers used for mutant identification.
Primers used for gene cloning into the pLIFE33 expression vector from cDNA.
Abbreviations and accession identification numbers for diterpene synthases, kaurene oxidases, steriod 5α-reductases and CYP71 family proteins used for phylogenetic analysis in this study.
Gene sequences used in enzyme co-expression studies including native sequences, synthetic sequences, and codon-optimized sequences for expression in E. coli.
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Ding, Y., Murphy, K.M., Poretsky, E. et al. Multiple genes recruited from hormone pathways partition maize diterpenoid defences. Nat. Plants 5, 1043–1056 (2019). https://doi.org/10.1038/s41477-019-0509-6
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