Department of Biotechnology, CTPD, School of Chemical and Lifesciences, Jamia Hamdard, New Delhi, India.
Division of Genetics, IARI- Indian Agricultural Research Institute, New Delhi, India.
PLoS One. 2023 Feb 6;18(2):e0260085. doi: 10.1371/journal.pone.0260085. eCollection 2023.
Stevia rebaudiana (stevia) contains commercially important steviol glycosides, stevioside and rebaudioside A, these compounds have insulinotropic and anti-hyperglycemic effect. Steviol, stevioside and rebaudioside-A have taste modulation and insulin potentiation activity. Stevia leaves are composed of steviol (2-5%), stevioside (4-13%) and rebaudioside-A (1-6%). Stevioside has after-taste bitterness, rebaudioside-A is sweetest in taste among all the glycosides present. Therefore, lower ratio of rebaudioside-A to stevioside has bitter after-taste, which makes stevia plants unpalatable. By over-expressing the genes, SrUGT76G1 and SrKO, we propose to increase the ratio of RebA to stevioside in stevia. Various lines were generated and amongst them, seven lines had both the transgenes present. Co-overxpresion of SrUGT76G1 and SrKO led to the increased concentration of RebA in all the seven transgenic lines (KU1-KU7) than control plant and RebA to stevioside ratio also increased significantly. Steviol, stevioside and RebA showed a differential concentration in all the seven lines, but the pattern was the same in all of them and the ratio of RebA to stevioside increased dramatically. In transgenic line 2 (KU2), RebA showed a steep increase in concentration 52% the rebaudioside-A to stevioside ratio increased from 0.74 (control) to 2.83. In overall all the lines, RebA showed a positive correlation with steviol and stevioside. Overexpression of SrKO led to an increase in steviol which increased the stevioside, overexpression of SrUGT76G1 ultimately increased RebA concentration. In conclusion, concentration of RebA increased significantly with co- overexpression of SrUGT6G1 and SrKO genes. Lines with increased RebA are more palatable and commercially viable.
甜菊糖（甜菊）含有具有商业重要性的甜菊糖苷，如甜菊苷和瑞鲍迪苷 A，这些化合物具有胰岛素分泌和降血糖作用。甜菊醇、甜菊苷和瑞鲍迪苷 A 具有味觉调节和胰岛素增效活性。甜菊叶由甜菊醇（2-5%）、甜菊苷（4-13%）和瑞鲍迪苷 A（1-6%）组成。甜菊苷有后苦味，瑞鲍迪苷 A 在所有糖苷中甜度最高。因此，瑞鲍迪苷 A 与甜菊苷的比例较低会产生后苦味，使甜菊植物口感不佳。通过过表达基因 SrUGT76G1 和 SrKO，我们提出增加甜菊中瑞鲍迪苷 A 与甜菊苷的比例。生成了各种品系，其中七种品系均存在两种转基因。SrUGT76G1 和 SrKO 的共过表达导致所有 7 种转基因株系（KU1-KU7）中 RebA 的浓度高于对照植物，RebA 与甜菊苷的比例也显著增加。甜菊醇、甜菊苷和 RebA 在所有 7 个品系中的浓度均有所不同，但所有品系的模式相同，RebA 与甜菊苷的比例急剧增加。在转基因株系 2（KU2）中，RebA 的浓度急剧增加 52%，RebA 与甜菊苷的比例从 0.74（对照）增加到 2.83。在所有株系中，RebA 与甜菊醇和甜菊苷呈正相关。SrKO 的过表达导致甜菊醇增加，从而增加了甜菊苷的含量，SrUGT76G1 的过表达最终增加了 RebA 的浓度。总之，SrUGT6G1 和 SrKO 基因的共过表达显著增加了 RebA 的浓度。RebA 含量增加的株系更可口，更具商业可行性。
