Characterization of Withania somnifera Leaf Transcriptome and Expression Analysis of Pathogenesis – Related Genes during Salicylic Acid Signaling

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.

Transcriptome analysis reveals in vitro cultured Withania somnifera leaf and root tissues as a promising source for targeted withanolide biosynthesis

“…In our current study, we generated a total of 249 million high-quality reads from in vitro -grown leaf and root tissues, more than the previously reported ESTs and transcriptome data [ 20 , 30 , 31 ]. We obtained a total transcriptome size of 183 Mbps with average transcript length of 1,033 bp (Table 1 ) which is comparatively better than a previous Withania 454 transcriptome study [ 20 ].…”

“…In both studies, the phenylpropanoid biosynthesis pathway was found to harbour the largest cluster of transcripts. In a recent study, Dasgupta et al [ 31 ] reported 184 pathways from their in vitro leaf transcriptome library. The additional pathways may be due to pathogenesis-related genes expressed in response to salicylic acid signalling in the source tissue of their study.…”

“…Initial efforts have been made to generate expressed sequence tags (ESTs) from in vitro tissues of W. somnifera [ 30 ]. In addition, leaf and root transcriptomes of field-grown tissues have been analysed to identify genes involved in withanolide biosynthesis [ 20 ], and very recently, analysis of the expression of pathogenesis-related genes has been carried out in leaf transcriptomes of W. somnifera [ 31 ]. However, no large-scale transcriptome information validated by expression profiling is available for in vitro tissues of W. somnifera .…”

Promoters of plant genes responsive to pathogen invasion

“…The absence of this hormone results in a delay in the activation of genes involved in the defense response (Baebler et al, 2014). The effect of salicylic acid results in an increase in the activity of pathogenesis related (PR) gene fam ilies (except PR10) and in the increased accumulation of secondary metabolites (that have antitumor and bacteriostatic effects) in the Withania somnifera L. medicinal plant (Ghosh Dasgupta et al, 2014). Phy topathogens induce a disturbance in the level of hor mone balance in plants rearranging the host transcrip tome work to its own advantage.…”

Validation of dbEST-SSRs and transferability of some other solanaceous species SSR in ashwagandha [Withania Somnifera (L.) Dunal]

“…It is a dicotyledonous plant of the family Solanaceae and widely used in traditional medical systems of India and Africa as adaptogens (physical and mental health promoter) or vitalizers (Dasgupta et al 2014). …”