Triterpene RDF: Developing a database of plant enzymes and transcription factors involved in triterpene biosynthesis using the Resource Description Framework.

Plants produce structurally diverse triterpenes (triterpenoids and steroids). Their biosynthesis occurs from a common precursor, namely 2,3-oxidosqualene, followed by cyclization catalyzed by oxidosqualene cyclases (OSCs) to yield various triterpene skeletons. Steroids, which are biosynthesized from cycloartenol or lanosterol, are essential primary metabolites in most plant species, along with lineage-specific steroids, such as steroidal glycoalkaloids found in the Solanum species. Other diverse triterpene skeletons are converted into triterpenoids, often classified as specialized compounds that are biosynthesized only in a limited number of plant species with tissue- or cell-type-specific accumulation in plants. Recent studies have identified various tailoring enzymes involved in the structural diversification of triterpenes as well as transcription factors that regulate the expression of these enzymes. However, the coverage of these proteins is scarce in publicly available databases for curated proteins or enzymes, which complicates the functional annotation of newly assembled genomes or transcriptome sequences. Here, we created the Triterpene RDF, a manually curated database of enzymes and transcription factors involved in plant triterpene biosynthesis. The database (https://github.com/ktamura2021/triterpene_rdf/) contains 532 proteins, with links to the UniProt Knowledgebase or NCBI protein database, and it enables direct download of a set of protein sequences filtered by protein type or taxonomy. Triterpene RDF will enhance the functional annotation of enzymes and regulatory elements for triterpene biosynthesis, in a current expansion of availability of genomic information on various plant species.