EST Analysis Predicts Putatively Causative Genes Underlying the Pharmaceutical Application of Glycyrrhiza uralensis Fisch

Glycyrrhiza uralensis Fisch is an important medicinal plant used not only as a natural sweetener but also for a variety of pharmaceutical applications. Even though there have been previous reports of genes putatively associated with the biosynthesis of the sweet compound glycyrrhizin, the absence of genomic information and the insufficient transcriptomic data for this plant still hinder sufficient insight into the causative genes underlying the pharmaceutical and culinary applications of Glycyrrhiza uralensis Fisch. In this study, we sequenced 5,276 ESTs from Glycyrrhiza uralensis Fisch, established 2,353 unique sequences based on clustering and performed comparative analysis of them. Of the 2,353 unique sequences, we found homologs and orthologs for 1,499 of them with similarity searches against the non-redundant protein database at NCBI using the BLASTX algorithm and against the InterPro database using hidden Markove model (HMM) methods. We have functionally classified 749 unique sequences using Gene Ontology (GO) terms, mapped pathways for 248 unique sequences with the Kyoto Encyclopedia of Genes and Genomes (KEGG) and predicted 30 secreted proteins. Based on their expression levels, we have identified genes encoding a novel beta-D-xylosidase, glutathione-S-transferase and arabinogalactan protein 16 that may function in the glycyrrhizin biosynthesis, anti-tumor activity and detoxifying activity of this very promising medicinal plant. Furthermore, the EST sequence information described in this paper could be a valuable resource for future scientific research projects on this plant, including genome sequencing and annotation and genetic diversity as well as functional genomics and molecular functional studies.