Biology subjects

McDowell, T.

Publications and source records attributed to McDowell, T..

2 recordsLinked to original sources

bioRxiv2026

Multi-Substrate Specificity of Isoflavone hydroxylases (GmIFH) Drive Isoflavonoid Diversification in Soybean

Isoflavone hydroxylases (IFHs, CYP81E) convert isoflavone aglycones into their respective hydroxylated intermediates, which direct legume isoflavones into specialized defense pathways. In soybean, their functions have been studied mostly in the context of the daidzein-derived glyceollin biosynthesis. Here we combine metabolomics-guided feature mining, phylogenetic analysis, heterologous enzymology, structural elucidation, and in planta metabolite validation to determine the functional landscape of the soybean IFH family. Analysis of a soybean isoflavonoid-enriched metabolomic dataset revealed unidentified hydroxyisoflavone features that co-accumulated with glyceollins, indicating branch chemistry that is not well-recognized. The systematic characterization of the repertoire of soybean CYP81E has demonstrated that 9 out of 11 GmIFHs are catalytically active and collectively span both 2'- and 3'- hydroxylation of the major soybean isoflavone aglycones. Among them, GmIFH9A showed broad substrate scope and regioselectivity, yielding canonical and previously unknown hydroxylated isoflavone products. NMR and LC-MS/MS were used to identify and validate the hydroxylated isoflavone products as 2'-hydroxyglycitein and 2'-hydroxyformononetin, whose presence was also confirmed in soybean roots, thus confirming two of the hidden soybean isoflavonoid network metabolites. Kinetic studies also indicated that, although the majority of GmIFHs prefer daidzein and genistein as substrates, a few isoforms are active towards methoxylated isoflavones as well, indicating functional divergence in this expanded family. Our findings collectively redefine soybean IFHs as a multi-functional enzyme module that expands the hydroxyisoflavone chemical space and reveals new biosynthetic entry points beyond canonical glyceollin pathway.

biochemistry↗

bioRxiv2024

Discovery of the missing cytochrome P450 monooxygenase cyclases that conclude glyceollin biosynthesis in soybean

Glyceollins are isoflavonoid-derived metabolites produced by soybean that hold great promise in improving human and animal health due to their antimicrobial, and other medicinal properties. They play important roles in agriculture by defending soybean against one of its most destructive pathogens, Phytophthora sojae. Longstanding research efforts have focused on improving accessibility to glyceollins, yet chemical synthesis remains uneconomical. The fact that some of the key genes involved in the final step of glyceollin biosynthesis have not been identified, engineering the accumulation of these important compounds in microbes is not yet possible. Although the activity of a P450 cyclase was inferred to catalyze the final committed step in glyceollin biosynthesis forty years ago, the enzyme in question has never been conclusively identified. This study reports, for the first time, the identification of three cytochrome P450 monooxygenase cyclases that catalyze the final steps of glyceollin biosynthesis. Utilizing P. sojae-soybean transcriptome data, along with genome mining tools and co-expression network analysis, we have identified 16 candidate glyceollin synthases (GmGS). Heterologous expression of these candidate genes in yeast, coupled with in vitro enzyme assays, enabled us to discover three enzymes capable of producing two glyceollin isomers. GmGS11A and GmGS11B catalyzed the conversion of glyceollidin to glyceollin I, whereas GmGS13A converted glyceocarpin to glyceollin III. The functionality of these candidates was further confirmed in planta through gene silencing and overexpression in soybean hairy roots. This groundbreaking study not only contributes to the understanding of glyceollin biosynthesis, but also demonstrates a new synthetic biology strategy that could potentially be scaled up to produce valuable molecules for crop and disease management.

biochemistry↗