Heading date of rice is controlled by complex mechanisms that respond
to several environmental conditions, such as daylength and temperature.
Factors controlling heading date include basic vegetative growth and photoperiod
sensitivity. Enhancer-Se1 (En-Se1), one of the photoperiod
sensitivity genes, was discovered in a perennial wild rice O. rufipogon
(W593) which dramatically delays heading in the presence of another photoperiod
sensitivity gene Se1 (Sano 1992). En-Se1 was reported to
be located on chromosome 6, between wx (Waxy endosperm) and Lcr
(Low crossability) (Sano 1992), but it has not been mapped on any molecular
linkage map. In this study, we carried out genetic mapping of En-Se1
using restriction fragment length polymorphism (RFLP) markers.
Near isogenic lines T65WxS6 (W593A) and T65wxSe1S6 (W593C)
contain segments of chromosome 6 of O. rufipogon (W593) from a
S6 gene (Hybrid sterility-6), to the Wx, and from the S6
to the Se1, respectively, in the genetic background of T65wx
(Sano 1992). An F2 population of 198 plants was produced by
crossing W593A and W593C. These F2 plants were grown from April
to August in an experimental paddy field in Tsukuba, Japan. More than
half of the F2 plants showed very late heading. Short-day treatment
was given to these plants to obtain self-pollinated seeds.
Total DNA of F2 plants was extracted from fresh leaf tissue
by the CTAB method (Murray and Thompson 1980). Southern hybridization
analysis was carried out following the procedure of Yamamoto et al.
(1998). DNA clones were selected from the distal side of the short arm
of chromosome 6 of a high-density linkage map (Harushima et al
1998) as probes for the RFLP analysis.
A total of 12 RFLP markers showed polymorphism between W593A and W593C,
and were used for linkage mapping (Fig. 1). Numbers of recombinations
detected between adjacent markers are summarized in Fig. 1. Plants in
which recombinations occurred in this region were used for a progeny test
to determine the genotype at the En- Se1 locus. Days to heading
of 50 self-pollinated progeny of each plant were measured. Genotypes of
F2 plants whose progeny headed from the middle to the end of
September were determined to be W593C type (en-Se1/en-Se1). Plants
whose progeny headed from the middle of September to the end of November
were determined to be heterozygous (En- Se1/en-Se1). Plants whose
progeny headed from the middle to the end of November were determined
to be W593A type (En-Se1/En-Se1). From these results along with
the results of RFLP mapping, En-Se1 was mapped between RFLP markers
C764 and R845, with 3 and 7 recombinants, respectively. No recombination
occurred with RFLP markers B174 and C1032 (Fig. 1).
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Harushima, Y., M. Yano, A. Shomura, M. Sato, T. Shimano, Y. Kuboki, T.
Yamamoto, S.Y. Lin, B.A. Antonio, A. Parco, H. Kajiya, N. Huang, K. Yamamoto,
Y. Nagamura, N. Kurata, G.S. Khush and T. Sasaki, 1998. A high density
rice genetic linkage map with 2275 markers using a single F2 population.
Genetics 148: 479-494.
Sano, Y., 1992. Genetic comparisons of chromosome 6 between wild and cultivated
rice. Jpn. J. Breed. 42: 561-572.
Yamamoto, T., Y. Kuboki, S.Y. Lin, T. Sasaki and M. Yano, 1998. Fine scale
mapping of quantitative trait loci, Hd-1, Hd-2 and Hd-3, controlling heading
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