| The Agrobacterium tumefaciens-mcdiated transformation conditions of sweetpotato, Ipomoea batatas (L.) Lam., were studied by using embryogenic cell suspension cultures of Xushu 18, a main cultivar in China. The A. tumefaciens strain EHA101 harboring a binary vector pROA93 with neomycin phosphotransferase gene (NPTII) and β-glucuronidase gene (GUS) was used in the present study.The optimal transformation conditions of Xushu 18 embryogenic cell suspension cultures were determined by systematical researches on A. tumefaciens concentration, subculture time, pretreatment time, cocultivation time, AgNO3 and AS concentrations in the cocultivation medium, and selection stress. The results showed that embryogenic cell suspension cultures subcultured for 3 days were optimal for the transformation. The A. tumefaciens concentration from OD600nm=0.1 to OD600nm=0.9 had no significant effect on the transformation. The pretreatment for 60 min with 0.45mol/L mannitol significantly promoted the transformation of embryogenic cell suspension cultures. The optimal concentrations of AgNO3 and AS in the cocultivation medium were 20 μmol/L and 100 μmol/L,respectively. The optimal cocultivation time was 2-4 days.Using the transformation conditions established above, we transformed the embryogenic cell suspension cultures of Xushu 18 with the A. tumefaciens strain EHA101 harboring a binary vector pROA93. The results indicated that the frequency of cell aggregates expressing transient GUS activity was 90.2%, and the frequency of kanamycin-resistant calluses expressing GUS activity was 94.4% at average. Through the selection culture, 676 kanamycin-resistant calluses were obtained from the infected 1538 cell aggregates, from which 18 plants have been regenerated so far. PCR assays showed that 16 of the 18 plants (88.9%) were transgenic plants. The plant regeneration from the remaining kanamycin-resistant calluses is being conducted.
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