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Wolf Prize in Agriculture
chromosome 10 short-arm-specific SSR markers (p-phi041, p-
phi117, and
p-umc1293) were present; none of the long-arm-
specific markers (p-umc1249, p-umc1196, p-umc1176, and p-
umc1084) tested was detected (22). We, therefore, assume that
the chromosome transmitted to offspring in every case is a
short-arm telocentric derivative of chromosome 10 (22). The
derived line disomic for the chromosome 10 short-arm telocen-
tric was labeled OMAdt10S.20 and seeds (F
3
offspring) have
already been distributed (Table 1).
The F
1
hybrid F
1
-5133-1 originated from crosses of Starter oat
with maize B73. This hybrid possessed the three maize chromo-
somes 4, 7, and 10 in addition to the haploid oat complement at
a young growth stage. In DNA samples from both the third and
fourth tillers (F
1
-5133-1
͞c and F
1
-5133-1
͞d), SSR markers were
present for chromosome 4 and chromosome 10. Although all
three short-arm-specific markers for chromosome 10 were
present in the two DNA samples, neither sample showed evi-
dence for long-arm-specific markers. Therefore, we assume that
chromosome 10, which was accompanied by maize chromosome
4, also was a telocentric short-arm derivative of chromosome 10.
PCR analysis of the three F
2
offspring from the panicles of the
third and fourth tiller of plant F
1
-5133-1 (Table 2) showed that
only two F
2
plants had the short-arm-specific SSR markers for
chromosome 10, and none had any of the long-arm-specific SSR
markers for chromosome 10. All three F
2
plants had the chro-
mosome 4-specific SSR markers. All six F
2
offspring from the
F
1
-5133-1
͞a panicle were positive for B73 chromosome 4, three
as monosomic and three as disomic additions. The tiller F
1
-5133-
1
͞b did not set seed.
The generation of a fertile disomic telocentric addition for
chromosome 10 (OMAdt10S.20) is a major breakthrough in our
efforts to develop a complete series of fertile oat–maize addition
lines (22). However, this observation raises the question of why
does only the short arm of an added maize chromosome 10
transmit in oat. Does the long arm possess a gene that prevents
transmission in this alien background? High sterility occurs in
the highly stable whole chromosome 10 addition in GAF-Park
oat and the two independent events of short-arm derivatives of
chromosome 10 in Sun II and Starter oat, where the long-arm
telocentrics could not be established. The situation appears
similar to the difficulties of generating a disomic euplasmic
addition line for Betzes barley chromosome 1H and for its
long-arm telosome 1HL in Chinese Spring wheat (25). The
difficulties in wheat (26–28) appear to be caused by the inter-
action of the gene Shw (sterility in hybrid with wheat) with the
wheat background causing sterility. However, the sterility was
alleviated by the simultaneous addition of monosomic or disomic
chromosome 6H to the 1H addition (29). Perhaps we could select
(oat
ϫ maize)F
1
hybrids for the simultaneous additions of other
chromosomes with chromosome 10 to possibly allow fertility and
transmission of the whole chromosome 10. In addition, it may be
feasible to use additional maize genotypes that possess a differ-
ent allele of the presumed gene on chromosome arm 10L
responsible for the sterility. In the corresponding wheat–barley
addition situation, chromosome 1H of the closely related wild
barley (Hordeum vulgare L. subsp. spontaneum) was added to
wheat without causing a severe effect of sterility (30).
Oat–Maize Chromosome 1 RHs.
Monosomic oat–maize chromo-
some 1 addition seeds, the foundation for the development of
oat–maize chromosome 1 RH lines, were treated with
␥ rays at
two levels. These levels were 180 BC
1
seeds treated with 40 krad
and 120 BC
1
seeds treated with 35 krad. A total of 46 maize-
positive plants, as indicated by the presence of the markers
Grande 1 and
͞or CentA, were recovered from the 40-krad
treatments. The 35-krad treatment generated 54 maize-positive
plants. These 100 BC
1
plants were allowed to self-pollinate. Of
these, 91 panicles produced 340 BC
1
F
2
offspring that tested
negative and 171 BC
1
F
2
offspring that tested positive for maize
chromatin in their genomes, indicating successful transmission of
maize segments. It is notable that after the
␥ radiation treatment
of 300 monosomic addition seeds, only 100 plants retained their
maize chromosomes or a diminutive maize chromosome deriv-
ative. This finding indicates that a majority of the breaks
generated maize fragments that were eliminated from somatic
tissues. Earlier results showed a certain level of somatic insta-
bility for whole chromosome 1 addition plants resulting in
chromosome loss (7, 10).
A set of 45 SSR markers distributed along maize chromosome
1 was used to determine by a presence vs. absence test for each
marker approximate points of maize chromosome breakage in
the 171 BC
1
F
2
plants. All 45 SSR markers were present in 98
BC
1
F
2
plants, which represent 50 families. These plants were
considered as possessing either a whole maize chromosome
without a break or a reciprocal oat–maize translocation. These
plants will be self-pollinated, and offspring of those with recip-
rocal translocations will be selected for the segregating translo-
cated chromosomes. Nine BC
1
F
2
plants, forming five families,
showed complex rearrangements, including interstitial deletions
and multiple translocations with oat. Forty-four BC
1
F
2
plants
constituted 21 families, each representing one likely independent
(chromosome rearrangement) event (Table 3). These 44 RH
plants were placed into 10 panel groups, with plants within a
group resulting from similar maize chromosome breaks based on
marker analysis (Table 3 and Fig. 2). Fig. 2 illustrates the
definition of eight segments by seven breaks in selected RH lines
for maize chromosome 1 representing the 10 groups (Table 3).
Plants with only one break in their maize chromosome, and thus
possessing only one deficiency or one oat–maize translocation,
are shown in the first panel (Fig. 2). The markers shown in the
left column are the first and last marker present or absent and
frame the breakpoints. The points define six segments on the
short arm (p-umc1354 to p-umc168), one large segment spanning
the centromere region (p-umc1626 to p-mmc0041), and one
additional segment on the long arm (p-bnlg1720 to p-umc2244).
The apparently single breakpoint in the long arm of chromo-
Table 3. Groups of RH lines from independent chromosome
mutation events that define the same breakpoints on
chromosome 1
Treatment,
krad
No. of BC
1
plants
No. of BC
1
F
2
plants with
similar breaks
No. of
independent
events*
Panel
group
40
2
3
2
1
35
3
3
3
1
40
1
1
1
2
40
1
3
1
3
35
1
2
1
4
35
1
1
1
5
40
1
1
1
6
35
2
2
2
7
35
2
2
2
8
40
2
20
2
9
35
4
5
4
9
35
1
1
1
10
*Each irradiated BC
1
plant producing offspring with a rearranged added
maize chromosome either as a deletion or a translocation with an oat
chromosome represents at least one independent mutation event. Chromo-
somal BC
1
-plant mutants, however, are not necessarily based only on one
single rearrangement event because of potentially different mutations in
different embryo cells during irradiation. Thus, the resulting chimeric nature
of the radiated BC
1
plants among their different tillers can produce and
transmit more then one maize chromosome derivative to the corresponding
BC
1
F
2
-offspring plants.
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͉ www.pnas.org͞cgi͞doi͞10.1073͞pnas.0403421101
Kynast et al.
38_2006-7 Phillips.p65
06-Mar-09, 7:49 PM
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