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Zusammenfassung:
To ensure food security, maize (Zea mays) is a model crop for understanding useful traits underlying stress resistance. In
contrast to foliar biochemicals, root defenses limiting the spread of disease remain poorly described. To better understand
belowground defenses in the field, we performed root metabolomic profiling and uncovered unexpectedly high levels of the
sesquiterpene volatile b-selinene and the corresponding nonvolatile antibiotic derivative b-costic acid. The application of
metabolite-based quantitative trait locus mapping using biparental populations, genome-wide association studies, and nearisogenic
lines enabled the identification of terpene synthase21 (ZmTps21) on chromosome 9 as a b-costic acid pathway
candidate gene. Numerous closely examined b-costic acid-deficient inbred lines were found to harbor Zmtps21
pseudogenes lacking conserved motifs required for farnesyl diphosphate cyclase activity. For biochemical validation,
a full-length ZmTps21 was cloned, heterologously expressed in Escherichia coli, and demonstrated to cyclize farnesyl
diphosphate, yielding b-selinene as the dominant product. Consistent with microbial defense pathways, ZmTps21
transcripts strongly accumulate following fungal elicitation. Challenged field roots containing functional ZmTps21 alleles
displayed b-costic acid levels over 100 mg g21 fresh weight, greatly exceeding in vitro concentrations required to inhibit the
growth of five different fungal pathogens and rootworm larvae (Diabrotica balteata). In vivo disease resistance assays, using
ZmTps21 and Zmtps21 near-isogenic lines, further support the endogenous antifungal role of selinene-derived metabolites.
Involved in the biosynthesis of nonvolatile antibiotics, ZmTps21 exists as a useful gene for germplasm improvement programs targeting optimized biotic stress resistance.
