(go
to KOMUGI Home) (go
to WIS List) (go
to NO.71 Contents)
Results
Plants lacking one or two marker characteristics appeared in the
F1 plants by crossing between the marker line as female
and CS-Gc1aGc1a, thereas only a few mutants of Q were
observed from the reciprocal crosses (Table
1,
Fig.
1). Since mutants
did not appear in the control F1, it is clear that
Gc1a, induced the mutations. The mutation frequencies were
different among the genes (chi2
=12.5, df = 4 ), and
the mutation spectra in both 1985 and 1986 were similar. Except for
one case, chimeric mutants were not observed among the F1
mutants.
Germination of the F1 seeds was reduced when
CS-Gc1aGc1a was used as the male parent due to the presence
of many non-viable shriveled seeds (Table
2). On the other
hand, shriveled seeds were not produced by the reciprocal crosses nor
by the control crosses.
Discussion
Three important features of Gc1a as a mutational inducer
were revealed by the present study. Firstly, Gc1a causes
mutations at higher frequency when it is transferred from the male
gamete. Secondly, mutational frequencies are different among the five
genes observed. Thirdly, mutational events must occur only in the
first zygotic cell since it was observed that Gc1a derived
from the male gamete mutated the genes from the female gamete and
that most F1 mutants were not chimeric.
The first and third features of Gc1a as described above
suggest that the Gc1a gene was activated in the male gametes,
and inactivated before the first zygotic cell division. The genes
originating from the male gametes also may have been mutated by the
activated Gc1a gene. However, this was not detectable due to
lack of marker genes besides Q in the male gametes. The
mutants of the Q gene, for which mutation frequency was higher
than among the other genes investigated, may have included those
originating from the male allele. On the other hand, Gc1a
derived from the female gamete hardly mutated the genes of male
gametes with the exception of a few speltoid mutants which may be
attributable to the mutation of Q from the female gamete.
Tsujimoto and Noda (1989, 1990) reported that most mutants of the
Q gene caused by Gc1a or its related gene, Gc1b,
are involved in chromosomal breakage at proximal sites of the
Q locus and subsequent deficiency of the regions including
Q. The break points did not appear to have fixed locations
although it is unclear whether they are dispersed at random along the
chromosomes. If the mutants of the other genes observed in the
present study were caused by chromosornal deficiency of the segments
including the genes, the mutational frequency of the marker genes
would be proportional to the distance of the genes from the
centromere. The genes Q and Hg are located in distal areas
which do not link with the centromere (Rao 1983; McIntosh and Bennett
1978), C and Hp1 link with the centromere with 2.26 and
approximately 30 cM, respectively
(Rao1972; Driscoll
and Sears 1965). The distance of B1 has not been determined.
However, Tsujimoto and Noda (1990) recently reported from the data of
a deletion mapping that it must physically comprise 13% of the distal
end of whole long arm of chromosome 5A. The mutational frequencies of
the five genes tended to correlate positively with the distance from
the centromere. However, more F1 plants should be examined
before drawing a concrete conclusion.
References
Endo TE (1990) Gametocidal chromosomes and their induction of
chromosome mutations in wheat. Jpn J Genet 65: 135-152.
Driscoll CJ and Sears ER (1965) Mapping of a wheat-rye translocation.
Genetics 51: 439-443.
McIntosh RA and Bennett FGA (1978) Telocentric mapping of genes
Pm3a and Hg on chromosome 1A of hexaploid wheat. Cereal
Res Comm 6: 9-14.
Rao MVP (1972) Mapping of the compactum gene C on
chromosome 2D of wheat. Wheat Inf Serv 35: 9.
Rao MVP (1983) Telocentric mapping of the squarehead (vulgare)
gene Q on chromosome 5A of hexaploid wheat. Wheat Inf Serv 56:
12-13.
Tsujimoto H and Tsunewaki K (1985) Hybrid dysgenesis in common wheat
caused by gametocidal genes. Jpn J Genet 60: 565-578.
Tsujimoto H and Noda K (1989) Structure of chromosome SA of wheat
speltoid mutants induced by the gametocidal genes of Aegilops
speltoides. Genome 32: 1085-1090.
Tsujimoto H and Noda K (1990) Deletion mapping by gametocidal genes
in common wheat: Position of speltoid suppressor (Q) and
beta-amylase (beta-Amy-A2) genes on chromosome 5A. Genome (in
press).
<--Back
(go
to KOMUGI Home) (go
to WIS List) (go
to NO.71 Contents)