The Unified Grass Genome: Synergy in Synteny
- Jeffrey L. Bennetzen1,2 and
- Michael Freeling3
- 1Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907; 3Department of Plant Biology, University of California, Berkeley, California 94720
This extract was created in the absence of an abstract.
The grasses, members of the family Gramineae or Poaceae, are represented by over 10,000 species (Kellogg and Birchler 1993). Three of the domesticated grasses, rice, wheat, and maize, account for about half of total world food production. Although the oldest known grass fossils have been found in paleocene-eocene deposits that are ∼50–60 million years old (Crepet and Feldman 1991), morphological and molecular clock data suggest that the grasses had a monophyletic (single) origin over 70 million years ago (Linder 1986;Clark et al. 1995).
Grasses are morphologically distinct from other plant families but are also highly diverse in morphology and growth habit. Grass species differ greatly in chromosome number and genome size. The genome of rice, for instance, is >11-fold smaller than the genome of barley (Arumuganathan and Earle 1991), despite their equivalent diploid states and apparently similar morphological and physiological complexity.
Grass Genome Colinearity
The use of common sets of low-copy-number DNA markers, often coding sequences, in the mapping of grass genomes has indicated that the gene content of different grass species does not vary greatly (Hulbert et al. 1990; Ahn et al. 1993; Kurata et al. 1994). Rice and barley, for example, do not differ by even twofold in the average number of genomic restriction fragments that hybridize to the same low-copy-number probes (A.E. Van Deynze, M.E. Sorrells, and S.R. McCouch; http://greengenes.cit.cornell.edu:80/anchors/). Much of the difference in genome size is attributable to differences in amounts of repetitive DNA (Flavell et al. 1974); larger genomes like barley or wheat are composed of >75% repetitive DNA, whereas smaller genomes like rice contain less <50% repetitive DNA (Flavell et al. 1974;Deshpande and Ranjekar 1980). A recent study has shown that retrotransposons inserted between genes account for the majority of the repetitive DNA in some large genome grasses, like …
