Regeneration and Agrobacterium-mediated transformation of japonica rice varieties developed for a cold region

So far, a large number of transformation systems have been established for japonica rice, but only a few have been reported for cold-region varieties. In our study, we established highly efficient tissue culture systems for two cold-region rice cultivars, Dongnong 427 and Longdao 14. Plant growth regulator (PGR) levels were optimized by an orthogonal experimental design. The culture ability, constituted by induction and differentiation rate, served as the detection index of orthogonal experiments. The optimal combinations of PGRs for callus induction and regeneration of Dongnong 427 and Longdao 14 were 1 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D) + 2 mg/l 6-benzyladenine (BA) + 4 mg/l kinetin (KIN) + 0.2 mg/l α-naphthaleneacetic acid (NAA) and 1 mg/l 2,4-D + 4 mg/l 6-BA + 4 mg/l KIN + 0.5 mg/l NAA, respectively. Agrobacterium strain EHA 105 containing the plasmid pCAMBIA1301 was used for transformation. The frequency of transient transformation was expressed as the ratio between the number of calli showing GUS expression and the total number of calli kept for staining. The highest transformation efficiency in Dongnong 427 was obtained when calli were immersed in 0.272 OD600 (optical density determined at 600 nm) for 10 min. While it was best for Longdao 14 calli to be infected with 0.592 OD600 for 20 min. Infected calli of the two varieties were co-cultivated on two pieces of sterile filter paper moistened with 1 ml liquid co-cultivation medium for three days. The expression of the GUS gene was confirmed by PCR analysis of plants of both varieties.