Abstract:

Agrobacterium mediated transformation has been used very successfully in some monocot plant such as rice (Oryza sativa L.) and maize (Zea mays L.); by which the transgenic plants obtain stronger resistance or better characters. But the efficiency of Agrobacterium mediated transformation system is still not so high as our expectation. Upland rice is a variety of rice (Oryza sativa L.), which has many good characters, such as drought resistance, and tolerance to sterile soil. Upland rice has been praised as one of the new source of food supplies in the 21st century in China. However, studies on the Agrobacterium mediated transformation system of upland rice are less compared with these of rice, and a lot of problems that affected the transformation efficiency should be solved. So setting up an effective transformation system of upland rice is still a challenge to investigators. Several important factors affecting upland rice transformation mediated by Agrobacterium were investigated with 4 upland rice cultivars.
In this paper callus induced from mature embryos of upland rice seeds were used mediated as explants to study the factors affecting the transformation rate. Callus were collected in a sterile trigonal bottle, Agrobacterium suspension was then added to the bottle, and vortexed for 30 s, followed by a 20 min of soaking in the bacteria solution. The callus were then transfered on co-cultivation medium(C-C1 or C-C2) in Petri plates and cultured in the dark for 3 days. After washed with sterile water, the explants were then put onto SX medium containing hygromycin for selection. After 6–8 weeks, surviving callus were transferred to differentiation medium. Then, the induced seedlings in 4–5 centimeters long were transferred onto root-inducing medium Finally, they were transplanted into soil when the roots had formed, and identified by PCR and Southern blot.
The transformation rate was affected by five factors in this process. NB medium was suitable for callus induction and subculture. Re-suspending the strain by AAM-AS medium before transformation could improve the resistant callus rate significantly. After infected by the strain, the callus were put on the 2 layers of sterile filter papers (d=12 cm) absorbed 4 mL C-C2 medium for co-cultivation, instead of being on agar medium, which could improve the resistant callus rate of NPT from 2% to 31.7%. Before selection and regeneration, desiccation for 2 days on sterilized filter papers could increase the resistant callus rate. Adding 10 mg L^-1AgNO₃ or 8 mg L^-1CuSO₄ into the differentiation medium could improve the regeneration rate, especially for the callus subculturd for 2 months or longer. many putative transgenic plants identified by PCR were acquired by using this transformation procedure, and southern blot analysis showed the target gene integrated in most transgenic plants just by single copy.

Key words: Upland rice, Agrobacterium mediated transformation, Co-culture, Differentiation