The efficiencies of generating selectable markerfree (SMF) transgenic rice through two transformation methods were compared using four indica and japonica varieties as materials. One is by using a single twin TDNA binary vector in one Agrobacterium strain. The twin TDNA binary vector pYH592 is composed of two separate TDNA regions, one carrying the antisense Wx gene while the other the HPT gene. The other one, known as twovector system, is by using two separate binary vectors in two separate Agrobacterium cultures. The results indicated that the average cotransformation frequencies of the antisense Wx gene and the HPT gene were 10.1% and 45.0% for the four rice varieties, the SMF transgenic plants could be found in the offsprings of 55.6% and 60.0% cotransformants, and the effectivenesses of generating markerfree transformants were 5.6% and 27.0%, respectively, in the twovector system and the twin T-DNA binary vector system.
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