Engineering and optimization of the 2-phenylethylglucosinolate production in Nicotiana benthamiana by combining biosynthetic genes from Barbarea vulgaris and Arabidopsis thaliana

Among the glucosinolate (GLS) defense compounds characteristic of the Brassicales order, several have been shown to promote human health. This includes 2-phenylethylglucosinolate (2PE) derived from homophenylalanine (HPhe). In this study, we used transient expression in Nicotiana benthamiana to validate and characterize previously predicted key genes in the 2PE biosynthetic pathway from Barbarea vulgaris and demonstrate the feasibility of engineering 2PE production. We used genes from B. vulgaris and Arabidopsis thaliana, in which the biosynthesis of GLSs is predominantly derived from HPhe and dihomomethionine, respectively. The resulting GLS profiles partially mirrored GLS profiles in the gene donor plant, but in both cases the profiles in N. benthamiana were wider than in the native plants. We found that BvBCAT4 is a more efficient entry enzyme for biosynthesis of both HPhe and dihomomethionine and that MAM1 enzymes determine the chain-elongated profile. Co-expression of the chain elongation pathway and CYP79F6 from B. vulgaris with the remaining aliphatic GLS core pathway genes from A. thaliana, demonstrated the feasibility of engineering production of 2PE in N. benthamiana. Noticeably, the HPhe-converting enzyme BvCYP79F6 in the core GLS pathway belongs to the CYP79F subfamily, a family believed to have substrate specificity towards chain-elongated methionine derivatives. Replacing the B. vulgaris chain elongation pathway with a chimeric pathway consisting of BvBCAT4, BvMAM1, AtIPMI and AtIPMDH1 resulted in an additional 2-fold increase in 2PE production, demonstrating that chimeric pathway with genes from different species can increase flux and boost production in an engineered pathway. Our study provides a novel approach to produce the important HPhe and 2PE in a heterologous host. Chimeric engineering of a complex biosynthetic pathway enabled detailed understanding of catalytic properties of individual enzymes - a prerequisite for understanding biochemical evolution - and with biotechnological and plant breeding potentials of new-to-nature gene combinations.

Aminorex identified in horse urine following consumption of Barbarea vulgaris; a preliminary report

Background Aminorex, (RS)-5- Phenyl-4,5-dihydro-1,3-oxazol-2-amine, is an amphetamine-like anorectic and in the United States a Drug Enforcement Administration [DEA] Schedule 1 controlled substance. Aminorex in horse urine is usually present as a metabolite of Levamisole, an equine anthelmintic and immune stimulant. Recently, Aminorex identifications have been reported in horse urine with no history or evidence of Levamisole administration. Analysis of the urine samples suggested a botanical source, directing attention to the Brassicaceae plant family, with their contained GlucoBarbarin and Barbarin as possible sources of Aminorex. Since horsepersons face up to a 1 year suspension and a $10,000.00 fine for an Aminorex identification, the existence of natural sources of Aminorex precursors in equine feedstuffs is of importance to both individual horsepersons and the industry worldwide. Results Testing the hypothesis that Brassicaceae plants could give rise to Aminorex identifications in equine urine we botanically identified and harvested flowering Kentucky Barbarea vulgaris, (“Yellow Rocket”) in May 2018 in Kentucky and administered the plant orally to two horses. Analysis of post-administration urine samples yielded Aminorex, showing that consumption of Kentucky Barbarea vulgaris can give rise to Aminorex identifications in equine urine. Conclusions Aminorex has been identified in post administration urine samples from horses fed freshly harvested flowering Kentucky Barbarea vulgaris, colloquially “Yellow Rocket”. These identifications are consistent with occasional low concentration identifications of Aminorex in equine samples submitted for drug testing. The source of these Aminorex identifications is believed to be the chemically related Barbarin, found as its precursor GlucoBarbarin in Kentucky Barbarea vulgaris and related Brassicaceae plants worldwide.