Flavonoids and Isoflavonoids Biosynthesis in the Model Legume Lotus japonicus; Connections to Nitrogen Metabolism and Photorespiration

Abstract

Phenylpropanoid metabolism represents an important metabolic pathway from which originates a wide number of secondary metabolites derived from phenylalanine or tyrosine, such as flavonoids and isoflavonoids, crucial molecules in plants implicated in a large number of biological processes. Therefore, various types of interconnection exist between different aspects of nitrogen metabolism and the biosynthesis of these compounds. For legumes, flavonoids and isoflavonoids are postulated to play pivotal roles in adaptation to their biological environments, both as defensive compounds (phytoalexins) and as chemical signals in symbiotic nitrogen fixation with rhizobia. In this paper, we summarize the recent progress made in the characterization of flavonoid and isoflavonoid biosynthetic pathways in the model legume Lotus japonicus (Regel) Larsen under different abiotic stress situations, such as drought, the impairment of photorespiration and UV-B irradiation. Emphasis is placed on results obtained using photorespiratory mutants deficient in glutamine synthetase. The results provide different types of evidence showing that an enhancement of isoflavonoid compared to standard flavonol metabolism frequently occurs in Lotus under abiotic stress conditions. The advance produced in the analysis of isoflavonoid regulatory proteins by the use of co-expression networks, particularly MYB transcription factors, is also described. The results obtained in Lotus japonicus plants can be also extrapolated to other cultivated legume species, such as soybean, of extraordinary agronomic importance with a high impact in feeding, oil production and human health.

Current Perspectives on the Beneficial Effects of Soybean Isoflavones and Their Metabolites for Humans

“…The isoflavone biosynthetic pathway is divided into several branches that generally share common substrates resulting in strong and regulated flux channeling. Isoflavones have a distinct group of plant secondary metabolites that are produced from the phenylpropanoid pathway [17]. The precursor in the multistep pathway of isoflavone biosynthesis is the amino acid L-phenylalanine, which in the initiating step is stripped of its amine group to generate cinnamic acid after non-oxidative deamination via the enzyme phenylalanine ammonia lyase (PAL).…”

Pleiotropic Effects of Isoflavones in Inflammation and Chronic Degenerative Diseases

“…These secondary metabolites are formed by symbiotic relationship with the Rhizobia bacteria and the defense responses of leguminous plant [ 16 ]. Isoflavones are synthesized as part of the phenylpropanoid pathway, the same biosynthetic pathway of flavonoid biosynthesis [ 17 ]. The structures of the main isoflavones are presented in Figure 2 .…”

Characterization and Comparison of Bacterial Communities of an Invasive and Two Native Caribbean Seagrass Species Sheds Light on the Possible Influence of the Microbiome on Invasive Mechanisms

“…From the predicted pathways found, most were not relevant for conferring a possible advantage to the invasive species (considered mostly “housekeeping functions”), and some were plant-specific and not likely found in bacteria. For example, Halophila roots have shown a higher abundance of biosynthesis of isoflavonoids; these are plant secondary metabolites known to play an important role in adaptation to their environment, both as defensive and as chemical signals in symbiotic nitrogen fixation with rhizobia ( García-Calderón et al, 2020 ) and are not produced by bacteria. That means that there is a low representation of those pathways that could possibly bring advantage to the seagrasses, enhancing its importance as possible assets for the invasion facilitation.…”