Steviol glycosides correlation to genes transcription revealed in gibberellin and paclobutrazol-treated Stevia rebaudiana

Stevia rebaudiana contains steviol glycosides (SVglys) responsible for its sweet taste. The knowledge of some shared steps between gibberellin (GA) and SVglys biosynthesis made it imperative to study the effect of paclobutrazol (PBZ; a GA biosynthesis inhibitor) and GA itself on SVglys accumulation and transcription of their correlated genes. Plants were treated with GA and PBZ (10 mg L-1) in controlled greenhouse conditions. The results showed that GA and PBZ treatments increased or decreased, respectively, stevioside, rebaudioside A, B, C, F, rubusoside, steviolbioside, dulcoside A, and total SVglys contents. The rebaudioside A/stevioside ratio is considered as a parameter to measure the quality of Stevia extract. PBZ treatment increased the rebaudioside A/stevioside ratio which means less aftertaste bitterness of Stevia extracts. GA treatment had no significant effect on this ratio. The transcription of ent-KO, ent-KS1, ent-KAH, UGT76G1, UGT85C2 and UGT74G1 were maximally increased by GA and minimally by PBZ treatments, respectively. This might explain the higher or lower accumulation of SVglys by treatments with GA or PBZ, respectively. The results revealed the correlation between gene transcription and SVglys accumulation which is worth to study in depth to produce Stevia with higher SVglys and sweeter taste.