Reference "Grass genomes"

Reference ID

5390

Title

Grass genomes

Source

Proceedings of the National Academy of Sciences of the United States of America, 1998, vol. 95, pp. 1975-1978

Authors (6)

Bennetzen-J-L	SanMiguel-P
Chen-M	Tikhonov-A
Francki-M	Avramova-Z

Abstract

For the most part, studies of grass genome structure have been limited to the
generation of whole-genome genetic maps or the fine structure and sequence
analysis of single genes or gene clusters. We have investigated large contiguous
segments of the genomes of maize, sorghum, and rice, primarily focusing on
intergenic spaces. Our data indicate that much (>50%) of the maize genome is
composed of interspersed repetitive DNAs, primarily nested retrotransposons that
insert between genes. These retroelements are less abundant in smaller genome
plants, including rice and sorghum. Although 5- to 200-kb blocks of methylated,
presumably heterochromatic, retrotransposons flank most maize genes, rice and
sorghum genes are often adjacent. Similar genes are commonly found in the same
relative chromosomal locations and orientations in each of these three species,
although there are numerous exceptions to this collinearity (i.e.,
rearrangements) that can be detected at the levels of both the recombinational
map and cloned DNA. Evolutionarily conserved sequences are largely confined to
genes and their regulatory elements. Our results indicate that a knowledge of
grass genome structure will be a useful tool for gene discovery and isolation,
but the general rules and biological significance of grass genome organization
remain to be determined. Moreover, the nature and frequency of exceptions to the
general patterns of grass genome structure and collinearity are still largely
unknown and will require extensive further investigation.