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21. Distribution of recombination sites
in the 195-kb region surrounding the wx gene in rice
KHIN-THIDAR, Y. TANAKA, T. INUKAI and Y. SAN0 Meiotic recombination does not
occur uniformly in the chromosomes in plants or other eukaryotic organisms
(Puchta and Hohn 1996; Schnable et al. 1998). Inukai et
al.(1998) previously reported that the average frequency of recombination
in the wx locus in rice was 27.1 kb/cM, about 10 times higher than the
whole rice genome (250 kb/cM). This result suggests two different possibilities,
the wx intragenic region is specifically active for meiotic recombination
or the wx intragenic region resides in a recombinationally
active interval which is larger than the wx gene. We investigated
recombination sites in the 195-kb region surrounding the wx gene
in the present study.
The physical map of 300-kb including
the wx locus in rice had been constructed by Nagano et al. (1997).
By using seven RFLP probes (four cDNA clones C01, C02, C03 and C04, and
two genomic clones G01 and G02) on this map, recombination frequency and
distribution of recombination sites in the 195-kb region surrounding the
wx locus was investigated. To estimate the recombination frequency
in this region, 381 F2 plants of a cross between the Japonica
cultivar T65wx and the Indica cultivar IR36 were analyzed with
the DNA clones G0l and C04. The genomic DNA clone G01 was located at 72-kb
in the direction of 5' side of the wx gene while cDNA clone C04 was located
at 123-kb in the direction of 3' side of the wx gene (Fig. 1).
In all ten recombinants were detected in the F2 population
and the recombination frequency within the 195-kb region was estimated
as 148 kb/cM. This frequency was two times higher than the genome average,
but five times lower than the recombination frequency within the wx
locus. The distribution of recombination sites in this region was shown
in Fig. 1, suggesting that recombination sites were randomly distributed
in the 195-kb region rather than concentrated in the regions near the
wx locus. These results indicated that the wx intragenic
region is specifically active for meiotic recombination in the 195-kb
region.
References
Inukai,T., A. Sako, Khin-Thidar and Y. Sano, 1998. Frequency and distribution of intragenic recombination at the wx locus in rice. RGN 15: 169-170. Nagano, H., L. Wu, S. Kawasaki, Y. Kishima and Y. Sano, 1997. Construction of a 300-Kb BAC contig containing waxy locus in Japonica rice. RGN 14: 121-123. Puchta, H. and B. Hohn, 1996. From centiMorgans to base pairs: homologous recombination in plants. Trends Plant Sci. 1: 340-348. Schnable, P.S.,A.-P. Hsia and B.L. Nikolau, 1998. Genetic
recombination in plants. Curr. Opin. Plant Biol. 1:123-129.
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