Ken-Ichi NONONIURA1 Tsutomu KAWASAKI1, Atsushi YOSHIMURA1, Naoki KISHIMOT02 and Nobuo IWATA1
1) Faculty of Agriculture, Kyushu University, Fukuoka, 812 Japan
2) National Institute of Aerobiological Resources, Kannondai, Tsukuba City, 305 Japan
Tertiary trisomics (TT), cytogenetical variants with a translocated chromosome in addition to normal chromosome complement, are useful in determining arm location of marker genes, position of centromere and orientation of linkage maps. Therefore, these are produced and used for genetic analysis in some plants (Khush 1973). In rice, tertiary trisomics were reported to occur in the progenies of reciprocal translocation heterozygotes and plants exposed to atomic radiation (Nishimura 1961; Iwata 1970; Tateno 1978). The systematic development and utilization for gene mapping, however, has not been undertaken.
Recently, we started to develop tertiary trisomics through three-way crosses (primary trisomics/reciprocal translocations//normal disomics) and obtained 23 such trisomics (Table 1). Reciprocal translocations used in the three-way crosses had translocated chromosomes associated with the extra chromosomes of primary trisomics. In the F1 progenies of the three-way crosses, it is expected that two types of TT, two types of primary trisomic interchange heterozygotes, one type of primary trisomics and some other aneuploids would occur. In this study, TT was distinguished from other trisomics on the basis of their morphology and seed fertility.
Most tertiary trisomics transmitted to their selfed progenies. In addition, primary trisomics associated with TT appeared at low frequencies. The frequencies of pentavalent pairing at diakinesis or metaphase I were also high in most of the trisomics (Table 1).
We also attempted to construct the chromosome map of rice by locating the interchange points of tertiary chromosomes on RFLP linkage map using RFLP gene dosage analysis of Indica X Japonica hybrids with extra tertiary chromosomes derived from Japonica, by the methods given by McCouch et al. (1988) and Ideta et al. (1990). RFLP clones were obtained from Saito et al. (1991). Fig.1 shows the result of gene dosage analysis of RFLP clones mapped on chromosome 12 using TT 8 (1-12a). When probed with Npb 261, hybrid TT showed gene dosage effect in lane 3, while no dosage effect was observed with Npb 336. This result suggests that the interchange point of TT 8 is between both loci on the RFLP linkage map of chromosome 12.
Two TT lines can be developed from each reciprocal translocation through three-way crosses. More RFLP gene dosage analyses and cytological information of translocated chromosomes at pachytene, therefore, will make it possible to construct detailed chromosome maps of rice.
Table 1. List of tertiary trisomics obtained in this study =============================================================================== No. of cells which show No. of TT 1OII + 1V chromosome Tertiarya Combination ofb appeared in configuration trisomics three-way cross selfed progenies ============================ (Total plants) 1OII+1V cells Cell stagec (Total cells) observed =============================================================================== TT 1A(5-9) T 5/RT 1//Nip 74(172) 15(52) M TT 1B(5-9) T 5/RT 1//Nip 53(169) - - - TT 2 (1-9a) NT 9/RT 2//Nip 36(120) 11(93) M TT 3 (1-9b) NT 9/RT 3//Nip 109(355) 7(44) M TT 4 (9-12a) T 12/RT 4//Nip 32(172) - - - TT 6 (7-9) NT 9/RT 6//Nip 61(169) 9(81) M TT 7 (4-9) NT 9/RT 7//Nip 15(106) - - - TT 8 (1-12a) T 12/RT 8//Nip 71(174) 1(32) M TT 15 (1-4c) NT 4/RT 15//Nip 6(14) 19(50) D TT 16 (1-8a) NT 8/RT 16//Nip 15(62) 7(23) D TT 17A(3-12a) NT 12/RT 17//Nip 62(168) 20(50) D TT 17B(3-12a) NT 12/RT 17//Nip 14(61) 10(51) D TT 70 (1-5d) NT 5/RT 70//Nip 5(57) 3(7) D TT 102(3-12) NT 12/RT 102//Nip 75(196) - - - TT 104(1-10) NT 1O/RT 104//Nip 31(116) 1(6) D TT 111(1-9) NT 9/RT 111//Nip 48(130) 9(39) D TT 114(4-9) NT 4/RT 114//Nip 8(51) 27(46) D TT 117(3-4) NT 4/RT 117//Nip 28(95) - - - TT 118(3-12) NT 12/RT 118//Nip 45(131) 9(50) D TT 120(1-4) NT 4/RT 120//Nip 22(69) - - - TT 122(3-9) NT 9/RT 122//Nip 4(17) - - - TT 127(9-12) NT 9/RT 127//Nip 116(334) - - - TT 130(1-9) NT 9/RT 130//Nip 90(237) 28(43) D ==============================================================================a. The numbering system of tertiary trisomics lines corresponds to that of reciprocal translocations. For example, in case of TT 1 derived from the crosses of T 5/RT 1//Nipponbare, strain number of TT 1 corresponds to that of RT 1 (For RT number except RT 118 and 127, see list of translocation, RGN 7, p. 60-64).
In TT 1 and TT 17, two expected tertiary trisomics were selected in the progenies of single translocation homozygote. The authors intend to call both type "A" and "B" respectively, in order of the number of translocated chromosomes involving a centromere of the extra chromosomes of these two tertiary trisomics. But without any cytological information, "A" and "B" in this table are defined only as a matter of convenience.
The numbers in parentheses show translocated chromosome numbers.
c. D=diakinesis, M=metaphase I.
Fig. 1. Gene dosage analysis of RFLP clones, Npb 261 and 336, mapped on chromosome 12 using hybrid tertiary trisomics of TT 8 (1-12a). The map distance between XNpb261 and 336 is 11.1 cM. In each autoradiogram, lane 1 =tertiary trisomics, lane 2=hybrid disomics, lane 3=hybrid tertiary trisomics and lane 4=IR 24.
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