[Generation of selectable marker-free and vector backbone sequence-free Xa21 transgenic rice]

The dominant gene Xa21 with broad-spectrum and high resistance to Xanthomonas oryzae pv. oryzae (Xoo) was transferred into C418, an important restorer line of japonica hybrid rice in China using double right-border (DRB) T-DNA binary vector through Agrobacterium-mediated transformation. 17 transgenic lines were Xa21-positive with high resistance to the race P6 of Xoo through PCR analysis and resistance identification, among the total 27 independent primary transformants (T0) obtained. The subsequent analysis of the T1 progenies of these 17 T0 lines through PCR-assisted selection and resistance investigation showed that four Xa21 transgenic T0 lines could produce selectable marker-free (SMF) progenies. The frequency of primary transformants producing SMF progenies was 15%. In addition, PCR analysis also revealed these SMF progenies did not contain vector backbone sequence, and they were named as SMF and vector backbone sequence-free (SMF-VBSF) Xa21 transgenic plants. The further molecular and phenotypic analysis of the T2 and T3 progenies testified the homozygous SMF-VBSF Xa21 transgenic plants were obtained with high resistance to Xoo.