Modi Arpan, Litoriya Nitesh, Prajapati Vijay, Rafalia Rutul, Narayanan Subhash
Plant Tissue Culture Laboratory, Anand Agricultural University, Anand, Gujarat, India.
Dev Dyn. 2014 Sep;243(9):1067-73. doi: 10.1002/dvdy.24157. Epub 2014 Jul 18.
Stevioside is a diterpene glycoside found in Stevia rebaudiana Bertoni (Asteraceae) and is 200-300 times sweeter than sucrose. It is synthesized through a plastid localized 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway. Fifteen genes are involved in the formation of steviol glycosides (stevioside and rebaudioside A). In the present investigation, micropropagated plants were allowed to harden for one month during which transcriptional profiling of candidate genes was carried out. Sampling from all the plants was carried out during hardening at different time intervals (day 10, 20, and 30) along with control plants (day 0). Stevioside content was also measured.
Of 15 genes, 9 were up-regulated two-fold or greater. Nine genes were expressed at higher levels after 30 days than in the untreated controls. Moreover, these transcriptional differences were correlated with a significant enhancement in stevioside content from 0- (11.48%) to 30- (13.57%) day-old plants.
MEP pathway genes in stevia are expressed at higher levels during hardening, a change to vegetative growth from reproductive growth. Although there were higher transcript levels of candidate genes at the initial phase of hardening, the highest stevioside content was found after 30 days of hardening, suggesting translational/posttranslational regulatory mechanisms.
甜菊糖苷是一种二萜糖苷，存在于甜叶菊（菊科）中，甜度比蔗糖高200 - 300倍。它通过质体定位的2-C-甲基-D-赤藓糖醇-4-磷酸（MEP）途径合成。十五个基因参与甜菊糖苷（甜菊糖苷和莱鲍迪苷A）的形成。在本研究中，对微繁殖植物进行了为期一个月的炼苗处理，在此期间对候选基因进行了转录谱分析。在炼苗期间的不同时间间隔（第10天、20天和30天）以及对照植物（第0天）对所有植物进行采样。还测定了甜菊糖苷含量。
15个基因中，9个基因上调了两倍或更多。9个基因在30天后的表达水平高于未处理的对照。此外，这些转录差异与甜菊糖苷含量从0日龄植物（11.48%）到30日龄植物（13.57%）的显著增加相关。
甜叶菊中的MEP途径基因在炼苗期间表达水平较高，这是从生殖生长向营养生长的转变。尽管在炼苗初期候选基因的转录水平较高，但在炼苗30天后发现甜菊糖苷含量最高，这表明存在翻译/翻译后调控机制。
