Symposium: Comparative Genomics in Plants

Abs # 40002: Genome structure, function and evolution assessed by comparative sequence analyses of BAC-sized fragments of the maize, sorghum, rice, wheat, barley and Arabidopsis genomes.

Presenter:	Bennetzen, Jeff , maize@bilbo.bio.purdue.edu
Authors	Bennetzen, Jeff  (A)
Affiliations:	(A): Department of Biological Sciences, Purdue University

Plants vary tremendously in the size and complexity of their nuclear genomes, but mapping studies have shown that most of this variation is not associated with differences in gene content. My lab employs studies of homologous regions of different grass genomes to see how these genomes have evolved and how these differences may affect gene function. We have chosen regions with various interesting properties (representative chromosomal locations, interesting genes [Rp1, Vrn1, etc], for instance) for our comparative sequencing studies. By sequencing BACs from orthologous regions, we can find what is present in a genome, and how it has changed in various genome types over a variety of different time frames. Our results indicate that intergenic regions can be quite different without altering the order or content of genes. Both small genomes (e.g., rice, sorghum) and large genomes (e.g., wheat, barley) can have very high gene densities in some genic regions, indicating that repetitive DNAs are sequestered into mostly non-genic domains. Maize appears to be exceptional in having a general mixing of genic and non-genic blocks. The reasons for these differences are not absolutely clear, but are probably related to the type, specificities and recent activity of the transposable elements that make up most of this repetitive DNA. Our studies also indicate that the different components of a grass chromosomal region undergo very different rates of evolution, respond to very different levels of natural selection, and have very different life expectancies. Taken in total, this research has begun to explain why genomes vary so greatly, and why this variation seems to have relatively little effect upon gene function.