De novo transcriptome profiling and development of novel secondary metabolites based genic SSRs in medicinal plant Phyllanthus emblica L. (Aonla)

Phyllanthus emblica (Aonla, Indian Gooseberry) is known to have various medicinal properties, but studies to understand its genetic structure are limited. Among the various secondary metabolites, ascorbic acid, flavonoids, terpenoids, phenols and tannins possess great potential for its pharmacological applications. Keeping this consideration, we assembled the transcriptome using the Illumina RNASeq500 platform, generating 39,933,248 high-quality paired-end reads assembled into 1,26,606 transcripts. A total of 87,771 unigenes were recovered after isoforms and unambiguous sequences deletion. Functional annotation of 43,377 coding sequences against the NCBI non-redundant (Nr) database search using BlastX yielded 38,692 sequences containing blast hits and found 4685 coding sequences to be unique. The transcript showed maximum similarity to Hevea brasilensis (16%), followed by to Jatropha curcas (12%). Considering key genes involved in the biosynthesis of flavonoids and various classes of terpenoid compounds, thirty EST-SSR primer sequences were designed based on transcriptomic data. Of which, 12 were found to be highly polymorphic with an average of 86.38%. The average value for marker index (MI), effective multiplicity ratio (EMR), resolution power (Rp) and polymorphic information content (PIC) was 7.20, 8.34, 8.64 and 0.80, respectively. Thus, from this study, we developed newly EST-SSRs linked to important genes involved in the secondary metabolites biosynthesis that will be serving as an invaluable genetic resource for crop improvement including the selection of elite genotypes in P. emblica and its closely related Phyllanthaceae species.