Seed shattering is a common trait among wild rice species and related
to rice domestication. Eiguchi and Sano (1990) identified Sh3,
a gene with the largest effect on seed shattering in Oryza glumaepatula.
Sh3 is tightly linked to RFLP marker R1427 on chromosome
4 (Sobrizal et al. 1999). In this study, we performed linkage analyses
of Sh3 using introgression lines of two wild rice species, O.
meridionalis Ng (W1625) and O. rufipogon Griff. (Acc. IRGC105715).
To perform genetic dissection of the characteristics of A-genome wild
rice species, we developed several series of chromosomal segment introgression
lines with a Japonica variety Taichung 65 (T65) genetic background. Among
them, introgression lines of two wild rice species, O. meridionalis
(O. meridionalis introgression lines, merILs) (Kurakazu et al.
2001) and O. rufipogon (O. rufipogon introgression lines,
rufILs), were used for the analyses of seed shattering. Shattering plants
were observed in BC4F1 populations during the process
of introgression line development. Two BC4F2 populations
of merILs and rufILs that were obtained from self-pollinating shattering
BC4F1 plants were used for mapping.
Field observations showed that BC4F2 population
of merILs segregated 105 shattering and 28 non-shattering plants. The
segregation fitted a 3:1 ratio ( chi2 = 1.105, P = 0.29),
suggesting that seed shattering was controlled by a single dominant gene.
Linkage analysis was subsequently performed using RFLP markers C1016,
R1427 and C107 of chromosome 4. The seed shattering gene
was tightly linked to R1427 without recombination (Fig 1). Moreover,
the analysis of rufILs yielded similar results. The BC4F2
population of rufILs segregated 86 shattering and 18 non-shattering plants;
the segregation fitted a 3:1 ratio (rufILs; chi2 = 3.282, P
= 0.07). RFLP analysis revealed that the seed shattering gene of rufILs
was also linked to R1427 with no recombinant. Since Sobrizal et
al. (1999) located Sh3 from O. glumaepatula (hereafter,
the allele is designated as Sh3-glum) in the same map position
of chromosome 4, the alleles identified from O. meridionalis and
O. rufipogon in this study were designated as Sh3-mer and
Sh3-ruf, respectively. This co-linear linkage map suggested that
three wild rice species, O. glumaepatula, O. meridionalis
and O. rufipogon, have a common shattering gene, Sh3. The
loss of function of Sh3 in O. sativa might be a primary
cause for rice domestication.
This study was supported by Bio-oriented Technology Research Advancement
Institution (BRAIN), Japan.
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