Botany Department, Faculty of Science, 81528, South Valley University, Aswan, Egypt.
J Plant Physiol. 2011 Jul 1;168(10):1136-41. doi: 10.1016/j.jplph.2011.01.030. Epub 2011 Apr 7.
A short-term experiment was designed to measure the transcript levels of downstream genes contributing to the biosynthesis of steviol glycosides. Stevia rebaudiana plants were subjected to long- and short-day conditions for different time intervals. Samples from both lower and upper leaves were collected. Using quantitative real-time polymerase chain reaction, the transcript levels of three UDP-dependent glycosyltransferases, UGT85C2, UGT74G1 and UGT76G1, were studied. The results were compared with the steviol glycoside contents measured in the leaves, which were quantified by reversed phase HPLC. In the same daylength condition, steviol glycoside concentration and the transcript levels of the three UGT genes were higher in upper leaves than in lower leaves. Steviol glycosides accumulated more in plants under short-day conditions. Under these conditions, a highly significant correlation was found between UGT85C2 transcription and total steviol glycoside accumulation in the upper leaves. This suggests that the glycosylation of steviol to form steviolmonoside is the rate-limiting step in the glycosylation pathway of steviol glycosides. In these upper leaves, a relatively high accumulation of rebaudioside A compared to stevioside was also observed, however, without correlation with the transcription of UGT76G1.
设计了一个短期实验来测量参与甜菊糖苷生物合成的下游基因的转录水平。将甜菊植物置于长日和短日条件下不同的时间间隔。采集来自下部和上部叶片的样本。使用实时定量聚合酶链反应，研究了三个 UDP 依赖性糖基转移酶 UGT85C2、UGT74G1 和 UGT76G1 的转录水平。将结果与通过反相高效液相色谱法测量的叶片中甜菊糖苷含量进行比较。在相同的日照条件下，上部叶片中的甜菊糖苷浓度和三个 UGT 基因的转录水平均高于下部叶片。在短日条件下，甜菊糖苷积累更多。在这些条件下，在上部叶片中发现 UGT85C2 转录与总甜菊糖苷积累之间存在高度显著的相关性。这表明甜菊醇的糖基化形成甜菊苷是甜菊糖苷糖基化途径中的限速步骤。在这些上部叶片中，与甜菊醇相比，赤藓醇 A 的积累相对较高，但与 UGT76G1 的转录没有相关性。
