Transcriptome sequencing on different ages of Saraca asoca bark: Insights from tannin biosynthetic pathways and EST-SSR marker design

Abstract

The bark of Saraca asoca is extensively used for treating gynecological issues, primarily due to its tannin content. This study focused on transcriptome sequencing of young (BY; 0–6 years), middle-aged (BM; 6–12 years), and old (BO; >12 years) Ashoka barks. The de novo assembly produced 1,37,451 unigenes of 1,31,647,800 bp from BY, 1,16,825 unigenes of 1,15,283,571 bp from BM, and 81,825 unigenes of 68,553,092 bp from BO samples. These transcripts closely matched with Glycine max and Cajanus cajan. Transcriptome analysis identified key genes and enzymes in the tannin biosynthetic pathway, with higher levels of phenylpropanoid and flavonoid pathways observed in middle-aged samples, followed by young and old samples. Pathway enrichment analysis indicated that the Differentially Expressed Genes (DEGs) were predominantly in the biosynthetic pathways of flavonoids, isoflavonoids, anthocyanins, terpenoids, and isoquinoline alkaloids. The study also examined the up-regulated and down-regulated DEGs involved in tannin production across the different sample comparisons, revealing the flavonoid pathway to be the most regulated. Additionally, 9612, 8053, and 4659 simple sequence repeats (SSRs) were identified from BY, BM, and BO transcripts, respectively. Fourteen EST-SSR markers specific to tannins were designed and validated, with one found to be polymorphic. This research represents the first report on transcriptome sequencing and EST-SSR markers from various ages of Saraca asoca bark, providing a foundation for future genetic mapping and conservation efforts of this vulnerable species.