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Elucidation of Juglone Synthesis in Black Walnut
Author(s) -
McCoy Rachel M.,
Ye YaJin,
Widhalm Joshua R.
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.lb212
Subject(s) - juglone , biochemistry , arabidopsis , biology , complementation , metabolic engineering , mutant , biosynthesis , hydroxylation , naphthoquinone , enzyme , gene , botany
Juglone has the potential to serve as a novel, natural product‐based herbicide. Juglone is an allelopathic naphthoquinone secreted by black walnut trees and other members of the Juglandaceae family. Metabolic engineering strategies to harness juglone as a new bio‐based herbicide are hampered by a lack of knowledge about its biosynthesis. Labeling data suggest that juglone is produced via 1,4‐naphthoquinone (1,4‐NQ) from 1,4‐dihydroxynaphthoic acid (DHNA), which is also an intermediate in the synthesis of the photosynthetic naphthoquinone phylloquinone (PhQ; vitamin K 1 ). We, therefore, hypothesize that juglone is biosynthesized via a sequential decarboxylation and hydroxylation of DHNA derived from the PhQ pathway. Our first goal is to completely elucidate the plant pathways to synthesize DHNA. In Arabidopsis thaliana , all pathway enzymes to synthesize DHNA have been characterized except for DHNA‐CoA synthase. Based on homology to menB, the Escherichia coli DHNA‐CoA synthase gene involved in menaquinone (vitamin K 2 ) biosynthesis, we have identified an Arabidopsis DHNA‐CoA synthase that coexpresses with other PhQ pathway genes. Efforts are currently underway to test if the candidate encodes a functional DHNA‐CoA synthase by functional complementation of the E. coli menB − mutant and reverse genetic approaches in Arabidopsis . Our next goal is to functionally screen DHNA decarboxylase and 1,4‐NQ hydroxylase candidate genes identified by transcriptome mining in black walnut through transient coexpression in tobacco to reconstitute the juglone pathway, relying on endogenous DHNA pools. We envision that our results will one day enable production of juglone in resistant, engineered crop systems, circumventing the need to apply synthetic herbicides.