| dc.description.abstract | Centromeres are responsible for sister-chromatid cohesion, kinetochore formation, and
accurate transmission of chromosomes. Rice provides an excellent model for
organizational and functional studies of centromeres since several of its chromosomes
contain limited amounts of satellite and other repetitive sequences in their centromeres.
To facilitate molecular characterization of the centromeres, we screened several BIBAC
and BAC libraries of japonica and indica rice, using several centromere-specific repeat
elements as probes. The positive clones were identified, fingerprinted and integrated
into our whole genome physical map databases of the two rice subspecies. BAC/BIBACbased
physical maps were constructed for the centromeric regions of the subspecies. To
determine whether the genomic organization of the centromeres has changed since the
cultivated rice split from its progenitor and to identify the sequences potentially playing
an important role in centromere functions, we constructed a large-insert BIBAC library
for the wild progenitor of Asian cultivated rice, O. rufipogon. The library contains
24,192 clones, has an average insert size of 163 kb, and covers 5 x haploid genome of
wild rice. We screened the wild rice library with two centromere 8-specific overgo
probes designed from the sequences flanking centromere 8 of japonica rice. A BIBACbased
map was constructed for wild rice centromere 8. Two of the clones, B43P04 and
B15E04, were found to span the entire region of the wild rice centromere and thus
selected for sequencing the centromere. By sequencing the B43P09 clone, a 95%
genomic sequence of the long arm side of wild rice centromere 8 was obtained.
Comparative analysis revealed that the centromeric regions of wild rice have a similar
gene content to japonica rice, but the centromeric regions of japonica rice have
undergone chromosomal rearrangements at both large scale and nucleotide levels. In
addition, although the 155-bp satellite repeats showed dramatic changes at the middle
region, they are conserved at the 5' and 3' ends of satellite monomers, suggesting that
those regions might have important functional roles for centromeres. These results
provide not only new insights into genomic organization and evolution, but also a
platform for functional analysis of plant centromeres. | en |
