Abstract
BackgroundFabaceae plants appear to contain larger numbers of subclade IVa basic-helix-loop-helix (bHLH) transcription factors than other plant families, and some members of this subclade have been identified as saponin biosynthesis regulators. We aimed to systematically elucidate the diversification of this subclade and obtain insights into the evolutionary history of saponin biosynthesis regulation in Fabaceae.ResultsIn this study, we collected sequences of subclade IVa bHLH proteins from 40 species, including fabids and other plants, and found greater numbers of subclade IVa bHLHs in Fabaceae. We confirmed conservation of the bHLH domain, C-terminal ACT-like domain, and exon-intron organisation among almost all subclade IVa members in model legumes, supporting the results of our classification. Phylogenetic tree-based classification of subclade IVa revealed the presence of three different groups. Interestingly, most Fabaceae subclade IVa bHLHs fell into group 1, which contained all legume saponin biosynthesis regulators identified to date. These observations support the co-occurrence and Fabaceae-specific diversification of saponin biosynthesis regulators. Comparing the expression of orthologous genes in Glycine max, Medicago truncatula, and Lotus japonicus, orthologues of MtTSAR1 (the first identified soyasaponin biosynthesis regulatory transcription factor) were not expressed in the same tissues, suggesting that group 1 members have gained different expression patterns and contributions to saponin biosynthesis during their duplication and divergence. On the other hand, groups 2 and 3 possessed fewer members, and their phylogenetic relationships and expression patterns were highly conserved, indicating that their activities may be conserved across Fabaceae.ConclusionsThis study suggests subdivision and diversification of subclade IVa bHLHs in Fabaceae plants. The results will be useful for candidate selection of unidentified saponin biosynthesis regulators. Furthermore, the functions of groups 2 and 3 members are interesting targets for clarifying the evolution of subclade IVa bHLH transcription factors in Fabaceae.
Highlights
Fabaceae plants appear to contain larger numbers of subclade IVa basic-helix-loop-helixtranscription factors than other plant families, and some members of this subclade have been identified as saponin biosynthesis regulators
We extensively explored subclade IVa bHLHs in fabids and showed that Fabaceae plants possess a large number of subclade IVa members, which were classified into three groups based on phylogenetic analysis
GmbHLH327, 329, 331, 334, 337, and 345 were newly assigned to subclade IVa based on Basic Local Alignment
Summary
Transcription factors than other plant families, and some members of this subclade have been identified as saponin biosynthesis regulators. We aimed to systematically elucidate the diversification of this subclade and obtain insights into the evolutionary history of saponin biosynthesis regulation in Fabaceae. Triterpene saponins are a group of plant specialised (secondary) metabolites found widely across the plant kingdom [1]. The monocotyledonous plants in the genus Avena produce antifungal saponins, known as avenacins in the roots for protection against take-all disease [9]. Fabaceae (Leguminosae) plants produce structurally diverse triterpenes, including hemolytic saponins in Medicago truncatula, betulinic acid in Lotus japonicus, and glycyrrhizin in Glycyrrhiza uralensis, as well as a common group called soyasaponins [11,12,13,14,15]. Leguminous triterpenes affect symbiotic nodulation, as transgenic M. truncatula with elevated saponin content showed enhanced nodulation [16] and L
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
