Specialized metabolites provide key layers of innate immunity underlying crop resistance. However, challenges in resolving pathways limit demonstration of function and application. While constitutive benzoxazinoid production has long been appreciated as a primary chemical defense of maize seedlings, recently, inducible accumulation of acidic terpenoids has emerged as a predominant defense at later stages of development. To understand biosynthesis of maize zealexin terpenoid antibiotics imparting disease resistance, we integrated association mapping, large-scale pan-genome multi-omic correlations, enzyme-structure function studies and targeted mutagenesis. Together this defined a ten-gene pathway with three zealexin (Zx) gene clusters comprised of four sesquiterpene synthases (Zx1-4) and six cytochrome P450s (CYP) in the CYP71Z (Zx5-7) and CYP81A (Zx8-10) families that drive production of diverse antibiotic cocktails. Gene duplications, ensuring pathway resiliency to single null mutations, are combined with enzyme substrate-promiscuity to create a biosynthetic hourglass pathway utilizing diverse substrates to drive complex product accumulation. Zx pathway disruption through CRISPR/Cas9 editing results in a broad-spectrum loss of disease resistance. This work elucidating the genetic basis for complex biochemical phenotypes that drive disease resistance both defines dominant and characteristic maize chemical defenses while informing innovative strategies for transferring durable chemical immunity between crops.
Coauthors: Yezhang Ding – UC San Diego;Philipp Weckwerth – UC San Diego;Elly Poretsky – UC San Diego;Ahmed Khalil – UC San Diego;Evan Saldivar – UC San Diego;Bing Yang – University of Missouri;Eric Schmelz – UC San Diego