Several members of the Juglandaceae family produce juglone,a specialized 1,4-naphthoquinone(1,4-NQ)natural product that is responsible for the notorious allelopathic effects of black walnut(Juglans nigra).Despite its ...Several members of the Juglandaceae family produce juglone,a specialized 1,4-naphthoquinone(1,4-NQ)natural product that is responsible for the notorious allelopathic effects of black walnut(Juglans nigra).Despite its documented ecological roles and potential for being developed as a novel natural product-based herbicide,none of the genes involved in synthesizing juglone have been identified.Based on classical labeling studies,we hypothesized that biosynthesis of juglone’s naphthalenoid moiety is shared with biochemical steps of the phylloquinone pathway.Here,using comparative transcriptomics in combination with targeted metabolic profiling of 1,4-NQs in various black walnut organs,we provide evidence that phylloquinone pathway genes involved in 1,4-dihydroxynaphthoic acid(DHNA)formation are expressed in roots for synthesis of a compound other than phylloquinone.Feeding experiments using axenic black walnut root cultures revealed that stable isotopically labeled L-glutamate incorporates into juglone resulting in the same mass shift as that expected for labeling of the quinone ring in phylloquinone.Taken together,these results indicate that in planta,an intermediate from the phylloquinone pathway provides the naphthalenoid moiety of juglone.Moreover,this work shows that juglone can be de novo synthesized in roots without the contribution of immediate precursors translocated from aerial tissues.The present study illuminates all genes involved in synthesizing the juglone naphthoquinone ring and provides RNA-sequencing datasets that can be used with functional screening studies to elucidate the remaining juglone pathway genes.Translation of the generated knowledge is expected to inform future metabolic engineering strategies for harnessing juglone as a novel natural product-based herbicide.展开更多
基金This work was supported by start-up funds and a Showalter Trust Fund award for bioinformatics support from Purdue University to J.R.WThis material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE-1333468 to J.W.C. We thank Jim McKenna (Hardwood Tree Improvement and Regeneration Center, Purdue University) for providing black walnut seedlings and collecting tissues from mature trees, Elena Yakubova for technical assistance, and Jing Yuan for assistance with microscopy.
文摘Several members of the Juglandaceae family produce juglone,a specialized 1,4-naphthoquinone(1,4-NQ)natural product that is responsible for the notorious allelopathic effects of black walnut(Juglans nigra).Despite its documented ecological roles and potential for being developed as a novel natural product-based herbicide,none of the genes involved in synthesizing juglone have been identified.Based on classical labeling studies,we hypothesized that biosynthesis of juglone’s naphthalenoid moiety is shared with biochemical steps of the phylloquinone pathway.Here,using comparative transcriptomics in combination with targeted metabolic profiling of 1,4-NQs in various black walnut organs,we provide evidence that phylloquinone pathway genes involved in 1,4-dihydroxynaphthoic acid(DHNA)formation are expressed in roots for synthesis of a compound other than phylloquinone.Feeding experiments using axenic black walnut root cultures revealed that stable isotopically labeled L-glutamate incorporates into juglone resulting in the same mass shift as that expected for labeling of the quinone ring in phylloquinone.Taken together,these results indicate that in planta,an intermediate from the phylloquinone pathway provides the naphthalenoid moiety of juglone.Moreover,this work shows that juglone can be de novo synthesized in roots without the contribution of immediate precursors translocated from aerial tissues.The present study illuminates all genes involved in synthesizing the juglone naphthoquinone ring and provides RNA-sequencing datasets that can be used with functional screening studies to elucidate the remaining juglone pathway genes.Translation of the generated knowledge is expected to inform future metabolic engineering strategies for harnessing juglone as a novel natural product-based herbicide.
