Multiple genes recruited from hormone pathways partition maize diterpenoid defences

Area of Science:

• Plant Metabolism
• Biochemistry
• Evolutionary Biology

Background:

• Plant specialized metabolism evolves through gene duplication and divergence, but partitioning of hormone and defense pathways remains unclear.
• The intermediate ent-kaurene is crucial for gibberellin (GA) biosynthesis and a proposed precursor for maize antibiotics.

Purpose of the Study:

• To elucidate the biosynthetic pathway of maize kauralexins, a class of plant antibiotics.
• To investigate the evolutionary mechanisms partitioning GA and kauralexin biosynthesis from shared precursors.

Main Methods:

• Integration of transcriptional coregulation, genome-wide association studies (GWAS), enzyme assays, proteomics, and mutant analyses.
• Analysis of diterpene synthase activity and promiscuous cytochrome P450s.
• Characterization of a novel steroid 5α reductase involved in the pathway.

Main Results:

• Maize kauralexin biosynthesis initiates from ent-isokaurene, a positional isomer of ent-kaurene, utilizing a diterpene synthase pair from GA metabolism.
• Three promiscuous cytochrome P450s and a steroid 5α reductase catalyze the oxygenation and desaturation of ent-isokaurene.
• Divergence and differential expression of duplicated hormone-metabolic genes allow for antibiotic synthesis without disrupting primary metabolism or GA production.

Conclusions:

• Maize antibiotic biosynthesis is achieved through a specialized pathway diverging from gibberellin metabolism.
• Gene duplication and promiscuous enzyme activity provide a mechanism for evolving defense compounds without compromising essential hormone functions.