ISSN 1021-4437, Russian Journal of Plant Physiology, 2017, Vol. 64, No. 1, pp. 67–72. © Pleiades Publishing, Ltd., 2017.
Quantitative Analysis of Uridine Diphosphate Glycosyltransferase
UGT85C2, UGT74G1 and UGT76G1 Genes Expression
in Stevia rebaudiana under Different Irrigations
P. B e h r o o z i
, A. Baghizadeh
*, A. Saei
, and S. Kharazmi
Department of Biotechnology, Graduate University of Advanced Technology, Kerman, Iran
Department of Biotechnology, Institute of Sciences and High Technology and Environmental Sciences,
Graduate University of Advanced Technology, Kerman, Iran
Agriculture Biotechnology Research Institute of Iran, Isfahan, Iran
*e-mail: email@example.com; firstname.lastname@example.org
Received September 13, 2015
Abstract—Stevia rebaudiana Bertoni is known to the scientific world for its sweetness and steviol glycosides.
Steviol glycosides are the secondary metabolites responsible for the sweetness of stevia and have many med-
ical applications. They are synthesized by a biosynthesis pathway operating in the leaves. Stevioside (Stev)
and rebaudioside A (Reb A) are two main glycosides compounds of Stevia. Translation products of three Uri-
dine diphosphate glycosyltransferase candidate genes, UGT85C2, UGT74G1 and UGT76G1, were found to
have an activity towards the synthesis of Stev and Reb A. In this study, a experiment was designed to measure
the expression level of three candidate genes contributing to the biosynthesis of steviol glycosides under three
different irrigation intervals using quantitative real-time PCR analysis technique. Irrigation was done at 3, 6
and 9 days irrigation intervals, based on soil moisture content 90, 75 and 60% of field capacity (FC) respec-
tively. The results showed that soil water depletion up to 75% FC lead to significant increase in expression of
UGT85C2 and UGT74G1 genes, whereas a significant growth in expression of UGT76G1 gene occurred at
60% FC. Measurement of Reb A contents in treated leaves showed that a significant correlation between
UGT76G1 transcription and Reb A accumulation under 60% FC. Also, the comparison of expression pat-
terns of the three target UGT transcripts at 75 and 60% FC showed a highly significant difference in
UGT74G1 transcripts in comparison of UGT85C2 and UGT76G1 transcripts. These results indicated that
the highest value of Reb A/ Stev ratio as sweetness quality index likely belongs to 60% FC and suggested 9 days
irrigation intervals to improve the quantity and quality of glycoside profile by up-regulation and down-regu-
lation of mentioned genes.
Keywords: Stevia rebaudiana, rebaudioside A, stevioside, soil moisture depletion, irrigation intervals, uridine
diphosphate glycosyltransferase, quantitative real-time PCR, quantitative analysis of uridine diphosphate
glycosyltransferase gene expression
The sweetness of honey leaf plant, Stevia rebaudi-
ana Bertoni, is attributed to accumulation of steviol gly-
cosides or steviosides in the leaves, the concentrations
of each can vary widely depending on the genotype,
growth conditions and developmental stage [1–5]. Ste-
viol glycosides are tetracyclic diterpenoids derived
from steviol as the final step of glycosylation by uridine
diphosphate glycosyltransferase (UGT) . Their
intense sweetness and antidiabetic function has made
them the subject of significant scientific and commer-
cial interest [6–8]. Among eight different steviol gly-
cosides, rebaudioside A (Reb A) was detected as the
sweetest glycosides with reduced bitter aftertaste .
Varity of steviol glycosides are as a result of many gly-
cosiletransfrase reactions . UGT belongs to the gly-
cosyltransferase family, is the key enzyme of glycosyla-
tion, responsible for the transfer of the sugar residue
from an activated donor to an acceptor molecule .
Recently, three of these glycosyltransferases were dis-
covered: UGT85C2, UGT74G1 and UGT76G1 .
In S. rebaudiana, they trigger the down stream steps in
the synthesis of steviol glycosides. The aglycone ste-
viol has two hydroxyl groups, one belonging to the
C-19 carboxylic acid moiety and the other attached to
the C-13, both of which can be glycosylated [11, 12].
The addition of C-13-glucose and C-19-glucose to
steviol is catalyzed by UGT85C2 and UGT74G1,
respectively and finally glycosylation of C-3-glucose
The article is published in the original.
Abbreviations: FC—field capacity; qRT-PCR—quantitative real-
time polymerase chain reaction; Reb A—rebaudioside A; Stev—
stevioside; UGT—uridine diphosphate glycosyltransferase.