CS-6-3 - Elucidating the metabolic origins and pathways of specialized plant 1,4-naphthoquinones
Sunday, July 15
3:58 PM - 4:18 PM
Specialized plant 1,4-naphthoquinones are a diverse group of natural products that collectively facilitate ecological roles in plant-plant (allelopathy), plant-insect, and plant-microbe interactions. Metabolic pathways leading to the formation of specialized 1,4-naphthoquinones have independently evolved in several discrete angiosperm lineages. Though classical tracer studies revealed the upstream metabolites that provide precursors for each route, virtually all specialized 1,4-naphthoquinone pathway genes remain unknown. We hypothesize that certain specialized 1,4-naphthoquinone pathways rely on immediate precursors shared with or derived from pathways involved in synthesizing photosynthetic or respiratory quinones. Combining comparative transcriptomics with targeted metabolic profiling and stable-isotopic labeling, we provide evidence that biosynthesis of juglone, the specialized 1,4-naphthoquinone responsible for the allelopathic effects of black walnut (Juglans nigra) trees, uses biochemical steps shared with the phylloquinone pathway to synthesize its naphthalenoid moiety. Our data also indicate that juglone can be de novo synthesized in black walnut roots without the contribution of immediate precursors translocated from aerial tissues. This work has in effect uncovered five of the a priori seven genes needed to synthesize juglone from chorismate, the product of the shikimate pathway. It also points to the existence of critical regulatory factors to mediate carbon flux distribution between production of phylloquinone, a vital one-electron carrier in photosystem I, and juglone, which provides black walnut with competitive advantages for growth and development. The knowledge gained from this research is expected to inform synthetic biology approaches for harnessing juglone as a novel natural product-based herbicide. This study is also serving as a guide for the discovery of pathway genes involved in synthesizing specialized 1,4-naphthoquinones in other species being investigated by our group.
Rachel McCoy – Purdue University; Sagar Utturkar – Purdue University; Joseph Crook – Purdue University; Jyothi Thimmapuram – Purdue University