Plant Genomics by Visualization of Genomes, Chromosomes and Genes

摘要

Genomics, a branch of genetics concerned with the systematic molecular characterization of whole genome, is important for obtaining an overview of the genome organization and to provide the basic information for isolating specific genes or DNA sequences. At present various projects in many higher plants are at various stages of sequencing and genome analysis. The whole genomes in Arabidopsis and rice have been or soon will be fully sequenced. It is more than one decade now since the fluorescence in situ hybridization (FISH) was first applied to visualize the DNA sequences on the plant chromosomes. Since then the technique has become very important in the genome analysis of plants to assess the homology between the genomes and to locate the position of different genes and DNA sequences on the individual chromosomes or extended DNA fiber. Genomic in situ hybridization (GISH), an offshoot of FISH technique, is a powerful tool using total genomic DNA as a probe for visualizing genome homology between polyploid species and their progenitors and to supplement information on the genomic origin of the polyploids. With the improvement in detection sensitivity and resolution of FISH technique it is now possible to even detect unique sequences, as small as 1kb. Mapping of genes or DNA sequences on extended DNA fiber and intact cloned DNA has increased the resolution of FISH technique. The technique was successful in showing the distal position of most of the agronomically important genes on the chromosomes of the crop plants. The technique was also able to show the gene synteny in cereals, particularly in wheat and rice. Despite of the size differences in the genomes of wheat and rice gene synteny is conserved, even in large blocks often comprising entire chromosome. In comparison to rice large amount of DNA was lying in between the genes on the chromosomes of wheat. In the present paper important problems and prospects of chromosome research in the field of plant genomics will be discussed for the 21st century.