Faculty of Agriculture, Kyushu University, Hakozaki, Fukuoka, 812 Japan
Since the establishment of 12 linkage groups corresponding to the
haploid chromosome number of rice by Nagao and Takahashi (1963), we have been
investigating the relationships between the linkage groups and chromosomes
mainly by using trisomics and reciprocal translocations (Iwata and Omura
1971a, b, 1975, 1976, 1984; Iwata et al. 1984; Kurata et al. 1981; Sato
1976; Sato et al. 1982; Yoshimura 1982). Recently we have established the
relationships between all the chromosomes and linkage groups. The results
from different series of studies are summarized in Table 1.
Table 1. Relationships among chromosomes, trisomics and linkage groups in
rice
============================================================================= Chromosome Trisomics =========== =========== Linkage RT Karyotype Jap- Indica group Marker genes oni- ca ============================================================================= 1 K1O H Triplo 9 VII _Bp*,_Dn,_dp-2*,drp-2* V _I-Bf 2 K9 L Triplo 5 VI _bgl*,_d-1,_nl-2*,_ops*,_v-10(t)* IX _nl-1,_ri,spl-7*,spl-8* XII _gl 3 K1 O Triplo 1 III A,ch-5*,ch-6*,d-10*,_d-18,eg*,fs-2, _lax,Pn,Rd,rl-2*,spl-6*,_v-6*,shr-1* 4 K5 A Triplo 6 - _d-B*,_nal-2*,_rl-1,_spl-1* 5 K3 M Triplo 4 XI bc-1,ch-l*,_ch-2*,ch-3*,ch-7*,d-K-2*, _dl*,drp-3*,drp-4*,fc*,op*,rl-3*,spl-3*, stl*,v-1,_v-2*,v-5*,v-7*,z-3* 6 K6 B Triplo 3 I C,_ch-4*,_Cl,_dp-1*,spl-4*,v-3*,_ws*,_wx 7 K12 C Triplo 10 - _du*,_fl*,_pgl*,_Rf-1,_rk-2 8 K2 N Triplo 2 X bl-1,bc-3*,d-K-l*,d-K-4*,d-W*,_gh-2*, gh-3*,spl-2*,tri 9 K8 G Triplo 11 VIII d-C*,_D-K-3*,d-t*,_la,_sp*,_v-4*,_z-1*, z-2*,_v-9(t)* 10 K11 F Triplo 7 IV _d-6,_g,_ge*,_Rc,_rfs*,spl-5*,_v-11(t)* 11 K4 E Triplo 12 II d-2,d-11*,_lg,nal-1*,Ph*,Pl,_rk-1*,ylm* 12 K7 D Triplo 8 - _d-51*,_su*,_ur-2(t)*,_v-8*,_z-4* ============================================================================= RT - Arbitrarily numbered on the basis of studies of reciprocal translocations by Nishimura (1961). Karyotype - Numbered according to the length of somatic prometaphase chromosomes in descending order by Kurata and Omura (1978). Trisomics, Japonica - Derived from Nipponbare, classified morphologically (Iwata et al. 1970, 1984). Trisoics, Indica - Estblished by Khush et al. (1984). Marker genes - Shown by symbols used at Kyushu University, Dept. of Plant Breed. Underline (_)indicates genes whose location was determined by trisomic analysis. * indicates genes described by the staff of Kyushu University.
Linkage groups VII and V were associated with chromosome I which is the extra chromosome of the H-type trisomics. Genes Bp, Dn and dp-2 (linkage group VII) and I-Bf (V) showed trisomic ratios in crosses with the H-type trisomics (Iwata and Omura 1975). Similarly, linkage groups VI, IX and XII were found to be associated with chromosome 2 which is the extra chromosome of the L-type trisomics (Iwata and Omura 1976). The linkage relations between I-Bf and genes belonging to linkage group VII still remain unknown. Linkage relations among genes of linkage groups VI, IX and XII were confirmed by both conventional and reciprocal translocation methods (Yoshimura et al. 1982; Sato et al. 1982).
None of the Nagao and Takahashi's linkage groups could be assigned to chromosomes 4, 7 and 12. However, several genes were located on them through trisomic analysis (Iwata and Omura 1975; lwata et ai. 1984; Yoshimura et al. 1982; Sato and Shinjyo 1978). Their linkage relations still remain unknown. The linkage groups assigned to respective chromosomes are shown in Fig. 1.
Many of the mutant genes listed in Table 1 were induced by irradiation or application of chemical mutagenes, but additional marker genes are necessary for preparing detailed linkage maps. The numbering system of rice chromosomes is not standardized as yet. It may be based on the length of chromosomes, but there is no complete agreement between the order of length of chromosomes at pachytene stage and that at somatic prometaphase. The adoption of an acceptable system would depend upon discussions among rice geneticists in the future.
Fig. 1. Linkage maps for 9 chromosomes. Gene symbols follow those
traditionally used at Kyushu University.
References
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Iwata, N., T. Omura and H. Satoh, 1984. Ditto, V. Relationship between the twelve chromosomes and the linkage groups. Jpn. J. Breed. 34: 314-321.
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Kurata, N. and T. Omura, 1978. Karyotype analysis in rice, I. A new method for identifying all chromosome pairs. Jpn. J. Genet. 53: 251-255.
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