The legume symbiont Bradyrhyzobium elkanii produces rhizobitoxine, a natural product which controls ethylene production in host plants by inhibiting 1-aminocyclopropane-1-carboxylate (ACC) synthase. Rhizobitozine also functions as an inhibitor of cystathionine-�-lyase in the methionine biosynthesis pathway. The enzymes responsible for rhizobitoxine biosynthesis have been identified: RtxA, a dual-functional enzyme responsible for both the biosynthesis of serinol from dihydroxyacetone phosphate and the coupling of serinol with an O-acylhomoserine variant to form dihydrorhizobitoxine, the immediate precursor to rhizobitoxine; and rtxC, which oxidizes dihydrorhizobitoxine to rhizobitoxine. In order to identify the O-acylhomoserine substrate for RtxA, we have heterologously overexpressed the only predicted homoserine acyltransferase in the B. elkanii genome and preliminarily characterized the subtrate scope of this enzyme using UV-visible spectrometry. We have also successfully heterologously overexpressed RtxC and are working to reconstitute its activity. We are further interested in exploring the inhibition of the cystathionine-�-lyase metC by rhizobitoxine to understand how B. elkanii maintains endogenous production of methionine, a necessary amino acid, and have successfully heterologously overexpressed and reconstituted the activity of the protein MetC.

Rhizobitoxine biosynthesis and self-protection in <i>?Bradyrhizobium elkanii</i>

247th National Meeting (2014)

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Rhizobitoxine biosynthesis and self-protection in ?Bradyrhizobium elkanii