Effect of salicylic acid on stevioside and rebaudioside A production and transcription of biosynthetic genes in in vitro culture of Stevia rebaudiana

S. rebaudiana produces steviol glycosides including stevioside and rebaudioside A that are valuable as low calorie sweeteners. The objective of this study was to investigate the effects of salicylic acid elicitation and sampling times on the improvment of stevioside and rebaudioside A production and KA13H, UGT74G1 and UGT76G1 genes expression. The results showed that the addition of different concentrations of salicylic acid had different effects on stevioside and rebaudioside A production in a dosage-dependent manner. Among different concentrations of salicylic acid the highest amount of stevioside was 38.33 mg/g DW and the highest amount of rebaudioside A was 2.93 mg/g DW, observed 96 h after elicitation with 90 mg/L and 48 h after elicitation with 60 mg/L salicylic acid, respectively. Elicitation with salicylic acid increased KA13H and UGT74G1 genes expressions and decreased UTG76G1 gene expression. The correlation analysis indicated that, KA13H gene expression had a positive correlation with stevioside production. The UGT74G1 gene expression had a positive correlation with stevioside production and a negative correlation with rebaudioside A production. The UGT76G1 gene expression had a positive correlation with rebaudioside A and negative correlation with stevioside production. The qRT-PCR analysis indicated that, by increasing stevioside production under salicylic acid elicitation, the KA13H and UGT74G1 genes expression increased and UGT76G1 gene expression decreased.