Abstract
Coumestrol (CMS), a coumestan isoflavone, plays key roles in nodulation through communication with rhizobia, and has been used as phytoestrogens for hormone replacement therapy in humans. Because CMS content is controlled by multiple genetic factors, the genetic basis of CMS biosynthesis has remained unclear. We identified soybean genotypes with consistently high (Daewonkong) or low (SS0903-2B-21-1-2) CMS content over 2 years. We performed RNA sequencing of leaf samples from both genotypes at developmental stage R7, when CMS levels are highest. Within the phenylpropanoid biosynthetic pathway, 41 genes were tightly connected in a functional co-expression gene network; seven of these genes were differentially expressed between two genotypes. We identified 14 candidate genes involved in CMS biosynthesis. Among them, seven were annotated as encoding oxidoreductases that may catalyze the transfer of electrons from daidzein, a precursor of CMS. Two of the other genes, annotated as encoding a MYB domain protein and a MLP–like protein, may increase CMS accumulation in response to stress conditions. Our results will help to complete our understanding of the CMS biosynthetic pathway, and should facilitate development of soybean cultivars with high CMS content that could be used to promote the fitness of plants and human beings.
Highlights
Plants synthesize secondary metabolites to promote their own survival, and some of these compounds have antioxidant or antibiotic effects[1,2]
CMS is a soybean phytoalexin that is present in soybean leaves and roots, rather than seeds, and CMS content varies depending on environmental conditions and growth stage[21,30,31]
Based on the differentially expressed genes (DEGs) between high-CMS and low-CMS genotypes, as well as their functional co-expression network, we identified candidate genes involved in biosynthesis of CMS from daidzein
Summary
Plants synthesize secondary metabolites to promote their own survival, and some of these compounds have antioxidant or antibiotic effects[1,2]. CMS accumulates to high levels after drought stress in root, doubling the extent of mycorrhizal colonization[32,33] Because other isoflavones, such as daidzein and formononetin, are involved in signaling in rhizosphere plant-microbe interactions, CMS has been implicated in drought tolerance in legumes, an effect mediated through communication with mycorrhiza[33,34,35]. Due to the important implications of soybean isoflavones and phytoalexins for plant defense and human health, it would be valuable to identify the enzymes responsible for CMS biosynthesis from its precursor, daidzein. Knowledge of these enzymes would facilitate successful manipulation of CMS levels in planta
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