Identification of a BAC [bacterial artificial chromosomes] clone carrying the xa5 locus in rice
1998
Daichang Yang | Sanchez, A. | Khush, G.S. | Yingguo Zhu | Zhikang Li | Ning Huang (International Rice Research Inst., P.O. Box 933, 1099 Manila (Philippines))
The recessive gene, xa5, confers resistance to a broad spectrum of rice bacterial blight strains in the Philippines. To generate a physical map of the xa5 locus, three RFLP markers closely linked to the gene, RG556, RG207, and RZ390 were used to screen a rice bacterial artificial chromosome (BAC) library. The identified overlapping BAC clones formed two small contigs. The contigs were extended to both sides by chromosome walking and merged into one by DNA fingerprinting. The final physical map consists of 14 BAC clones and covers 580 kb. Genetic analysis of an F2 population showed that two RFLP markers, 28N22R and 40F20R, derived from the BAC clones in the contig were flanking xa5 indicating that the contig encompass the xa5 locus. To further delimit the location of xa5 locus, RFLP markers RG556 and RG207 were converted to sequence tagged sites and used to perform genetic analysis. The results indicated that the xa5 locus is located between RG556 and RG207. Among the BAC clones in the contig, one BAC clone, 44B4, hybridized to both markers, RG207 and RG556. Therefore, it is concluded that BAC clone, 44B4, carried the xa5 locus. This BAC clone have been used to screen a cDNA library constructed from IRBB5 which carry the resistant allele as a further step towards cloning xa5. Preliminary results indicated that the xa5 gene is different from the dominant gene Xa21
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