|Klein, Robert - Bob|
Submitted to: Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/26/2004
Publication Date: 2/1/2005
Citation: Kim, J., Klein, P.E., Klein, R.R., Price, J.H., Mullet, J.E., Stelly, D.M. 2005. Molecular cytogenetics maps of sorghum linkage groups 2 and 8. Genetics. 169:955-965. Interpretive Summary: Major advancements in science hinge on the development of new tools including a detailed understanding of the structure of chromosomes. Chromosomes are the structures found in cells that harbor genes, the tiny packets of genetic blueprint material that are found in all plants and animals and control all of the physical characteristics of these organisms. Our work focuses on improving major grain crops and, with detailed knowledge of chromosomes, the genetic blueprint will be visible and this information can make improving the plants more efficient. This study details a microscopic view of two sorghum chromosomes, and revealed that regions of each chromosome have a high density of genes whereas other chromosomal locations are largely devoid of these genetic blueprints. Understanding the structure of sorghum chromosomes and knowing where important genes reside will permit more efficient identification of genes that control the physical appearance of an organism. Information will be primarily used by fellow scientists but the work should ultimately result in better adapted, higher producing crop varieties available to American farmers.
Technical Abstract: To integrate genetic, physical and cytological perspectives of the sorghum genome, we selected 40 landed bacterial artificial chromosome clones that contain different linkage map markers, 21 from linkage group 2 and 19 from linkage group 8. Cocktails with multiple bacterial artificial chromosome clones were constructed for each chromosome. Comparison to the corresponding linkage map revealed full concordance of locus order between cytological and prior segregation analyses. The pericentromeric heterochromatin constituted a large quasi uniform block in each bivalent, and was especially large in the bivalent corresponding to linkage group 8. Centromere positions were progressively delimited using Fluorescent In Situ Hybridization to identify landed bacterial artificial chromosome clones for which the Fluorescent In Situ Hybridization signals visibly flanked the centromere. Alignment of linkage and cytological maps revealed that pericentromeric heterochromatin of these sorghum chromosomes is largely devoid of recombination, which is mostly relegated to the more distal regions, which are largely euchromatic. This suggests that the sorghum genome is thus even more amenable to physical mapping of genes and positional cloning than previously suggested. As a prelude to positional cloning of a fertility restorer gene, Rf1, Fluorescent In Situ Hybridization of bacterial artificial chromosome clones flanking the fertility locus were used to delimit the chromosomal position of the gene. Fluorescent In Situ Hybridization of bacterial artificial chromosome clones that contain the most proximal linkage markers enabled localization of this gene to a small euchromatic region of linkage group 8.