Abstract
Sterol glycosyltransferases (SGTs) catalyse transfer of glycon moiety to sterols and their related compounds to produce diverse glyco-conjugates or steryl glycosides with different biological and pharmacological activities. Functional studies of SGTs from Withania somnifera indicated their role in abiotic stresses but details about role under biotic stress are still unknown. Here, we have elucidated the function of SGTs by silencing SGTL1, SGTL2 and SGTL4 in Withania somnifera. Down-regulation of SGTs by artificial miRNAs led to the enhanced accumulation of withanolide A, withaferin A, sitosterol, stigmasterol and decreased content of withanoside V in Virus Induced Gene Silencing (VIGS) lines. This was further correlated with increased expression of WsHMGR, WsDXR, WsFPPS, WsCYP710A1, WsSTE1 and WsDWF5 genes, involved in withanolide biosynthesis. These variations of withanolide concentrations in silenced lines resulted in pathogen susceptibility as compared to control plants. The infection of Alternaria alternata causes increased salicylic acid, callose deposition, superoxide dismutase and H2O2 in aMIR-VIGS lines. The expression of biotic stress related genes, namely, WsPR1, WsDFS, WsSPI and WsPR10 were also enhanced in aMIR-VIGS lines in time dependent manner. Taken together, our observations revealed that a positive feedback regulation of withanolide biosynthesis occurred by silencing of SGTLs which resulted in reduced biotic tolerance.
Highlights
Sterol glycosyltransferases (SGTs) catalyse transfer of glycon moiety to sterols and their related compounds to produce diverse glyco-conjugates or steryl glycosides with different biological and pharmacological activities
The amipds construct was prepared by PCR based mutagenesis of miRNA159a of Arabidopsis thaliana and cloned into Virus-induced gene silencing (VIGS) vector (Supplementary Fig. 1b) Syringe infiltration of this amipds-VIGS construct into W. somnifera plants developed bleaching in the systemic leaves 15 to 20 days post inoculation (DPI) due to phytoene desaturase (PDS) gene silencing (Fig. 1a)
We have checked the level of PDS, by qRT-PCR analysis (Fig. 1c) which concludes that PDS mRNA expression was 75 to 90% less in the systemic tissue of amipds-VIGS lines than in control plants
Summary
Sterol glycosyltransferases (SGTs) catalyse transfer of glycon moiety to sterols and their related compounds to produce diverse glyco-conjugates or steryl glycosides with different biological and pharmacological activities. Down-regulation of SGTs by artificial miRNAs led to the enhanced accumulation of withanolide A, withaferin A, sitosterol, stigmasterol and decreased content of withanoside V in Virus Induced Gene Silencing (VIGS) lines. This was further correlated with increased expression of WsHMGR, WsDXR, WsFPPS, WsCYP710A1, WsSTE1 and WsDWF5 genes, involved in withanolide biosynthesis. Sterol glycosyltransferases (SGTs) in plants catalyze the transfer of glycon moieties to the sterols and their related compounds to generate steryl glycosides (SGs) or saponins These glyco-conjugated sterols play very important role in defense of the plant against abiotic stresses and plant pathogen interactions[11]. Extensive analysis of the role of SGTs in the glycosylation of terpenoids and their effect in the plant basal immunity is still lacking
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