Isoflavone Synthase Genes in Legumes and Non-leguminous Plants: Isoflavone Synthase

Amidst the vast number of diverse secondary metabolites of plants, isoflavonoids occupy a special place due to the wide range of their biological activities. The literature deals extensively with the positive effect of these well-known phytoestrogens on human health, including cancer prevention and the mitigation of menopause symptoms, as well as with the potential risks associated with their consumption. Isoflavonoids have considerable importance for plants themselves, particularly in the defense against pathogens and in the induction of rhizobial symbiosis. A complete description of biosynthetic pathway of these natural products and of the genetic background of this biosynthesis, constitutes a challenge in the metabolic engineering of isoflavonoid biosynthesis, especially in the case of crop-plants that are not natural producers of isoflavonoids. Isoflavone synthase plays a key role in the biosynthesis of isoflavonoids. The vast majority of over 1600 known isoflavone structures were found in legumes. However, isoflavonoids have been identified in many other species from over 60 families. Known IFS genes belong to the CYP93C subfamily of cytochrome P450. Due to very specific nature of the catalyzed reaction, we hypothesised that IFS genes in other species share high degree of homology with already cloned genes. We aimed to identify new IFS orthologues in non-leguminous isoflavoneproducing plant species: Cannabis sativa and Humulus lupulus (Cannabaceae), Ruta montana and Ruta graveolens (Rutaceae) and Nicotiana tabacum (Solanaceae). IFS sequences showed high degree of similarity, over 70% at the nucleotide level. The phylogenetic map demonstrates the evolutionary relation of IFS genes from congenial species and their relationship to other taxa. Non-leguminous isoflavone producers contain close IFS orthologues that are likely to catalyze the first step of isoflavone biosynthesis. This finding has the potential to be exploited for the control of isoflavone production in crop plants.