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Wheat Information Service
Number76: 54-55 (1993)


Origin of midget chromosome present in the rye cytoplasmic Chinese Spring

N. Nakata, M. Tomita and Y. Yasumuro

Faculty of Agriculture, Tottori University, Tottori 680


We found a diminutive chromosome in the rye cytoplasmic Chinese Spring ((cer)-CS) and named it "Midget chromosomes" (Nakata et al 1986). This chromosome has essential genes responsible for endosperm development and fertility in the rye cytoplasmic line and was derived from rye chromosome 1R (Nakata et al 1988). This study was conducted to locate the origin of the midget chromosome on chromosome 1R by producing deletion lines for 1R. The deletions of 1R were induced by the action of the gametocidal gene of chromosome 4S¹ of Aegilops longissima (Endo 1985).


Materials and methods

(cer)-CS with 1R and without the midget chromosome was obtained by the cross between (cer)-CS and Imperial Rye chromosome 1R addition Chinese Spring(CS) line. For induction of deletion 1R, (cer)-CS with 1R was crossed with chromosome 4S¹ addition CS line. The seeds of the 4S¹ addition line were kindly provided by Dr. T. R. Endo, Nara University. The structural changes of 1R were examined in the F₂ progenies, because all the vaible F₂ plants with rye cytoplasm have the essential genes for endosperm development which located on 1R. Chromosome 1R was recognized by the double bands on the end of short arm and the large band on the end of long arm by C-banding, and carried the Sec3 gene for high molecular seed storage protein at the region near the interstitial C-band of the long arm (Gustafson et al1990). Therefore, the presence or absence of the C-band and Sec3 gene were examined for identification of structural changes of 1R. Seed proteins for the Sec3 gene were fractionated by SDS-PAGE.


Results and discussion

Plump and shrivelled seeds were segregated in the F₂. Only the plump seeds have chromosome 1R or structurally changed 1R carrying the essential genes for endosperm development. These plump seeds were examined for inspecting the structural changes of 1R.

The expression of the Sec3 gene was recognized in 109 seeds out of 145 plump seeds of F₂ examined. Sixty-one of them germinated and grew. These plants were examined by C-banding with respect to chromosome 1R. The intact 1R was monosomic, or disomic in 51 plants. An isochromosome of the long arms of 1R was found in three plants. Monotelosome or ditelosomes of long arm of 1R were found in three plants. The translocated chromosome composed of the short arm of 1B and the long arm of 1R was found in three plants. The translocated chromosome composed of the long arms of 4A and 1R was found in one plant (Fig.1A-E). Thus, all of 61 plants having Sec3 gene had the long arm of 1R though ten of 61 plants did not have the short arm of 1R. This indicates that the long arm of 1R as well as the midget chromosome has the essential genes for endosperm development.

Out of 26 plump seeds showing no subunit of the Sec3 gene, five plants germinated and grew. However, the karyotypes of only two plants were identified by C-banding. The two plants had one small subterminal chromosome in addition to 42 chromosomes of wheat (Fig.1F). This chromosome was similar in size to the D genome chromosomes and must have the essential genes for endosperm development although it did not carry the Sec3 gene. This chromosome was presumed to be derived from 1R by the deletion of a large part of the terminal regions of both arms. This indicates that the loci of the essential genes for endosperm development is between the centromere and the Sec3 locus of the long arm. The midget chromosome must be derived from the region near the centromere on the long arm of chromosome 1R, because the chromosome was telocentric.


References

Endo TR (1985) An Aegilops longissima chromosome causing chromosome aberrations in common wheat. Wheat Inf Serv 60: 29.

Gustafson JP, Butler E an cIntyre (1990) Physical mapping of a low-copy DNA sequence in rye (Secale cereale L). Proc Natl Acad Sci USA 87: 1899-1902.

Nakata N, Yasumuro Y and Sasaki M (1986) Midget chromosome found in common wheat cv. Chinese Spring with rye cytoplasm. Wheat Inf Serv 63: 39-41.

Nakata N, Asami H, Yasumuro Y and Sasaki M (1988) Role and transmission of midget chromosome found in the rye cytoplasmic Chinese Spring line. Proc 7th Int Wheat Genet Symp 391-396.

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