Heat Stress Effect on the Expression of Some Steviol Biosynthesis Genes in Stevia Rebaudiana

Background and aim: stevia is one of the medicinal plants that use the sugar in its leaves as a non-caloric, informal sweetener. compared to sucrose and other synthetic sweeteners, it is more sweetening. various factors can lead to increased or decreased expression of glycoside biosynthesis pathway genes. heat is one of the abiotic stresses and one of the most important factors that cause changes in crop yield. the purpose of this study was to investigate the effect of heat stress on the expression of some genes of the glycoside biosynthesis pathway including kah, ugt85c2 and ugt74g1.methods: for 14 days, heat stress was applied at 37±1°c for 16 h during the day and 25±1°c during 8 h at night. real-time pcr was used to investigate the transcription pattern of kah, ugt85c2 and ugt74g1 genes, following heat stress.results: the results of this experiment showed that the transcript level of the kaurenoic acid hydroxylase (kah) gene was significantly up-regulated. also, the ugt74g1 gene transcription decreased significantly. but, the transcription decrease in ugt85c2 was not significant.conclusion: since kah that catalysis the hydroxylation of kaurenoic acid into steviol, which is a common precursor for sg biosynthesis increased, may heat stress has a positive effect on steviol production but hurts the transcription from steviol glycosides biosynthetic (ugt74g1) gene with no effect on ugt85c2 downstream gene regulation that transform steviol into steviolmonoside.