Reference "A complex history of rearrangement in an orthologous region of the maize, sorghum, and rice genomes"

Reference ID

8001

Title

A complex history of rearrangement in an orthologous region of the maize, sorghum, and rice genomes

Source

Proceedings of the National Academy of Sciences of the United States of America, 2003, vol. , pp. -

Authors (3)

Ilic-K	SanMiguel-P-J
Bennetzen-J-L

Abstract

The sequences of large insert clones containing genomic DNA that is orthologous
to the maize adh1 region were obtained for sorghum, rice, and the adh1-
homoeologous region of maize, a remnant of the tetraploid history of the Zea
lineage. By using all four genomes, it was possible to describe the nature,
timing, and lineages of most of the genic rearrangements that have
differentiated this chromosome segment over the last 60 million years. The rice
genome has been the most stable, sharing 11 orthologous genes with sorghum and
exhibiting only one tandem duplication of a gene in this region. The lineage
that gave rise to sorghum and maize acquired a two-gene insertion (containing
the adh locus), whereas sorghum received two additional gene insertions after
its divergence from a common ancestor with maize. The two homoeologous regions
of maize have been particularly unstable, with complete or partial deletion of
three genes from one segment and four genes from the other segment. As a result,
the region now contains only one duplicated locus compared with the eight
original loci that were present in each diploid progenitor. Deletion of these
maize genes did not remove both copies of any locus. This study suggests that
grass genomes are generally unstable in local genome organization and gene
content, but that some lineages are much more unstable than others. Maize,
probably because of its polyploid origin, has exhibited extensive gene loss so
that it is now approaching a diploid state.