Gibberellin reverses the negative effect of paclobutrazol but not of chlorocholine chloride on the expression of SGs/GAs biosynthesis-related genes and increases the levels of relevant metabolites in Stevia rebaudiana

Steviol glycosides (SGs) and gibberellins (GAs) share the same molecular basis. However, the coordination of their respective biosynthetic pathways is very intriguing. Thus, the present study aimed to investigate the role of plant growth regulators, gibberellic acid (GA 3 ), chlorocholine chloride (CCC), and paclobutrazol (PBZ), on the metabolism of Stevia rebaudiana and identify possible ameliorates of the evaluated parameters when CCC and PBZ-treated plants were subsequently treated with GA 3 . For this, explants were cultured in the absence or presence of 2 mg L −1 GA 3 , CCC, or PBZ (Step 1). After 20 days, half explants incubated with CCC and PBZ were treated with 2 mg L −1 GA 3 and the other half, as well as the rest of the explants, were sub-cultured in their respective initial conditions for 20 days (Step 2). GA 3 -treated plants showed increased stevioside and phenolic compounds content, as well as a downregulation of most of the SGs/GAs biosynthesis-related genes, with a more pronounced effect upstream of steviol. Following this trend, CCC downregulated some MEP pathway genes, including SrDXS, SrDXR, SrCDPS , and SrKS , and upregulated SrUGT6G1 . PBZ also upregulated SrUGT76G1 and inhibited five genes of the MEP pathway and all genes coding for kaurenoid pathway enzymes. The obtained results highlight the capability of GA 3 to reverse the negative effects of PBZ on the pattern of many transcripts and to additionally increase the stevioside content to levels comparable to those found in field-grown plants. Graphic abstract