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Tandem gene duplication drives the molecular evolution of orobanchol into a novel noncanonical strigolactone with weak germination-inducing activity toward root parasitic weeds in cowpea
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DOI：10.1093/pcp/pcaf048.png)
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Abstract
En 中文
Cowpea (Vigna unguiculata), a vital grain legume in West Africa, faces substantial yield losses due to the root parasitic weed Striga gesnerioides. The germination of Striga relies on cowpea-produced strigolactones (SLs), including orobanchol and orobanchyl acetate. In cowpea, SL biosynthesis involves a stereoselective BC-ring-forming factor (SRF), a dirigent domain-containing protein that catalyzes the conversion of 18-oxo-carlactonoic acid (18-oxo-CLA) to orobanchol. VuSRF-like, an SRF homolog, has been identified as a tandemly duplicated gene of VuSRF in the cowpea genome, although its function remains unclear. Herein, we identified VuSRF-like as an additional biosynthetic enzyme that catalyzes the two-step conversion of 18-oxo-CLA to a novel SL via orobanchol. Structural analysis revealed that this novel SL, designated as orobanchonoic acid, features a cleaved C ring and an oxidized hydroxy group at C-4. Orobanchonoic acid was detected in substantial amounts in cowpea root exudates but exhibited lower germination-inducing activity toward S. gesnerioides and other parasitic weeds compared to orobanchol. Genomic comparisons among related legume species suggested that the tandem duplication of SRF in cowpea drove the neofunctionalization of VuSRF-like, facilitating orobanchonoic acid biosynthesis. This study provides new insights into SL biosynthesis, providing new opportunities to investigate SL evolution and rhizosphere interactions.
Keywords:
biosynthesis
cowpea (Vigna unguiculata)
dirigent protein
root parasitic weed
strigolactone
tandem duplication
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