SHORT COMMUNICATION Gene transcription of steviol glycoside biosynthesis in Stevia rebaudiana Bertoni under polyethylene glycol, paclobutrazol and gibberellic acid treatments in vitro Shokoofeh Hajihashemi • Jan M. C. Geuns • Ali Akbar Ehsanpour Received: 6 October 2012 / Revised: 16 January 2013 / Accepted: 16 January 2013 / Published online: 14 February 2013 Ó Franciszek Go ´rski Institute of Plant Physiology, Polish Academy of Sciences, Krako ´w 2013 Abstract This experiment was carried out to measure the transcript levels of some genes involved in biosynthesis of steviol glycosides. Stevia rebaudiana plants were treated with polyethylene glycol (PEG), paclobutrazol (PBZ) and gibberellic acid (GA). Using quantitative real-time poly- merase chain reaction, the transcript levels of kaurene synthase (KS), kaurene oxidase (KO), kaurenoic acid hydroxylase (KAH) and three UDP-dependent glycosyl- transferases, UGT85C2, UGT74G1 and UGT76G1, were studied. The transcription of ent-KS1-1, ent-KAH and UGT74G1 were fairly stable under different treatments. The transcription of ent-KO, UGT85C2 and UGT76G1 significantly decreased by PBZ and PEG treatments. The results indicate that both PBZ and PEG treatments resulted in the same negative effect on genes transcription, which could not be reversed by GA treatment. Keywords Drought stress  Gibberellic acid  Paclobutrazol  Real-time quantitative PCR  Stevia rebaudiana  Steviol glycosides Abbreviations CPPS Copalyl diphosphate synthase Dul Dulcoside GA Gibberellic acid GGDP Geranylgeranyl-diphosphate GTs Glucosyltransferases KO Kaurene oxidase KS Kaurene synthase KAH Kaurenoic acid hydroxylase PBZ Paclobutrazol PEG Polyethylene glycol SB Steviolbioside SVglys Steviol glycosides ST Stevioside Reb Rebaudiosides UGT Uridine diphosphate-dependent glycosyltransferase Introduction Stevia rebaudiana (Bertoni) is well known for its high content of sweet steviol glycosides (SVglys) in its leaves (about 4–20 % of dry weight) depending on the cultivar and growth conditions (Geuns 2003). SVglys are glu- cosylated derivatives of the diterpenoid compound steviol. SVglys biosynthesis pathway shares some steps with Gib- berellic acid (GA) biosynthesis and paclobutrazol (PBZ) block the GA biosynthesis (Fig. 1). In Stevia, geranylger- anyl-diphosphate (GGDP) is converted into steviol by the consecutive action of four enzymes namely copalyl diphosphate synthase (CPPS), kaurene synthase (KS), kaurene oxidase (KO) and kaurenoic acid hydroxylase (KAH) (Brandle and Telmer 2007; Fig. 1). Different Communicated by Y. Wang. S. Hajihashemi  J. M. C. Geuns (&) Laboratory of Functional Biology, Kasteelpark Arenberg 31, BP 2436, 3001 Heverlee-Leuven, Belgium e-mail: Jan.Geuns@bio.kuleuven.be S. Hajihashemi  A. A. Ehsanpour Department of Biology, Faculty of Sciences, University of Isfahan, 81746-73441 Isfahan, Iran 123 Acta Physiol Plant (2013) 35:2009–2014 DOI 10.1007/s11738-013-1226-9