Abstract
Withania somnifera (L.) Dunal is a valued medicinal plant with pharmaceutical applications. The present study was undertaken to analyze the salicylic acid induced leaf transcriptome of W. somnifera. A total of 45.6 million reads were generated and the de novo assembly yielded 73,523 transcript contig with average transcript contig length of 1620 bp. A total of 71,062 transcripts were annotated and 53,424 of them were assigned GO terms. Mapping of transcript contigs to biological pathways revealed presence of 182 pathways. Seventeen genes representing 12 pathogenesis-related (PR) families were mined from the transcriptome data and their pattern of expression post 17 and 36 hours of salicylic acid treatment was documented. The analysis revealed significant up-regulation of all families of PR genes by 36 hours post treatment except WsPR10. The relative fold expression of transcripts ranged from 1 fold to 6,532 fold. The two families of peroxidases including the lignin-forming anionic peroxidase (WsL-PRX) and suberization-associated anionic peroxidase (WsS-PRX) recorded maximum expression of 377 fold and 6532 fold respectively, while the expression of WsPR10 was down-regulated by 14 fold. Additionally, the most stable reference gene for normalization of qRT-PCR data was also identified. The effect of SA on the accumulation of major secondary metabolites of W. somnifera including withanoside V, withaferin A and withanolide A was also analyzed and an increase in content of all the three metabolites were detected. This is the first report on expression patterns of PR genes during salicylic acid signaling in W. somnifera.
Highlights
Withania somnifera (L.) Dunal belonging to family Solanceae is commonly known as Ashwagandha or Indian ginseng and is a valued medicinal plant with pharmaceutical and nutraceutical applications
Yellowing of leaf discs was observed in all treatments by one hour of salicylic acid (SA) application and complete necrosis was observed in 20 mM SA treatment
Plantlets were sprayed with 5 mM SA in intervals as described earlier and a control with plantlets sprayed with sterile water was maintained, to document the effect of SA
Summary
Withania somnifera (L.) Dunal belonging to family Solanceae is commonly known as Ashwagandha or Indian ginseng and is a valued medicinal plant with pharmaceutical and nutraceutical applications. The phytochemical analysis of root and leaf tissues of this species has been extensively studied [1,2] and the major metabolites reported include alkaloids (isopelletierine, anaferine), steroidal lactones (withanolides, withaferins), saponins (sitoindoside VII and VIII) and withanolides. These chemical components possess antiinflammatory, anti-stress, antitumor, antioxidant, anti-aging, immunomodulatory properties, hemopoetic effect, rejuvenating effect and provide cardiovascular protection [3,4,5,6]. Other phytohormones like abscisic acid, gibberellins, auxins, cytokinins, and brassinosteroids are documented to regulate plant immune response [11,12] indicating that plant growth and defense are tightly linked [13]
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