Dirigent gene editing of gossypol enantiomers for toxicity-depleted cotton seeds
Axial chirality of biaryls can generate varied bioactivities. Gossypol is a binaphthyl compound made by cotton plants. Of its two axially chiral isomers, (–)-gossypol has biological activity in mammals and degrades more slowly, and its accumulation in cottonseeds poses health concerns. Here, we identified two extracellular dirigent proteins (DIRs) from Gossypium hirsutum, GhDIR5 and GhDIR6, which impart the hemigossypol oxidative coupling into (–)- and (+)-gossypol, respectively. To reduce cottonseed toxicity, we disrupted GhDIR5 by genome editing, which eliminated (–)-gossypol but had no effects on other phytoalexins, including (+)-gossypol, that provide pest resistance. Reciprocal mutagenesis identified three residues responsible for enantioselectivity. The (–)-gossypol-forming DIRs emerged later than its enantiocomplementary counterparts, from tandem gene duplications which occurred shortly after the cotton genus diverged. Our study offers insight into how plants control enantiomeric ratios, and how to selectively modify the chemical spectra of cotton plants and thereby improve crop quality.