Elicitor-Induced Transcriptional Changes of Genes of the Steviol Glycoside Biosynthesis Pathway in Stevia rebaudiana Bertoni

Stevia rebaudiana is a medicinal plant widely used as a sweetener, and the sweetening power comes from the diterpenoid glycosides known as steviol glycosides (SGs). The studies of gene expression patterns in response to elicitors treatment are of extreme importance for biotechnological purposes. Methyl jasmonate (MeJa), spermidine (SPD), salicylic acid (SA), and paclobutrazol (PBZ) (100 A mu M) were applied to stevia plants growing in a hydroponic system to examine the effect of these elicitors along the time (24, 48, 72, and 96 h). SGs' contents and transcription levels of fifteen genes involved in the three stages comprising their biosynthesis pathway were evaluated. The results provide direct evidence that HDR, GGDPS, CDPS, KS, KO, and KAH are elicitor-responsive genes and they can be effectively regulated at least at the transcriptional level. MeJa and SPD treatments resulted in positive effects on the transcription of SGs biosynthetic genes, with SPD exhibiting the highest number of regulated genes at 48 h of exposure. PBZ treatment down-regulated genes encoding kaurenoid enzymes. SA treatment did not affect transcription of UGT85C2, UGT74G1, and UGT76G1 and decreased stevioside levels. Overall, this study offers new insights into the transcriptional response mechanisms in S. rebaudiana plants under the effect of the elicitors MeJa, SPD, SA, and PBZ.