ABSTRACT

Map-based cloning is defined as the isolation of a gene based on its position on the genetic map. The overall objective for utilizing a map-based cloning system in cotton is to go from a phenotype, an important agronomic trait, in the field to the isolation of the gene(s) in the laboratory^a.

The overall strategy for map-based cloning is to: 1) Map the target gene(s); 2) Determine the relationship between genetic and physical distance by physically mapping the region(s) using the most closely linked molecular markers; 3) Chromosome walk in a cotton yeast artificial chromosome library (YAC) to the target genets) using the most closely linked markers as starting points; 4) Identify the target gene on the YAC (e.g. mutant complementation).

Our laboratory is developing a map-based cloning system for cotton, in conjunction with a high density RFLP map^b,c, aimed at the isolation of agriculturally important genes. To this end we have: 1) Developed a method for the isolation and manipulation of very high molecular weight cotton DNA (megabase DNA) for physical mapping and YAC cloning; 2) Isolated and mapped a set of NotI halflinking clones useful for long-range physical mapping; 3) Generated over 800 cotton YACs with a insert size range of 50 to 250 kb.

Development of a map-based cloning system for cotton is important because cotton is the world's leading textile fiber. By combining a high-density RFLP map with an effective map-based cloning system, many agronomically important genes (e.f. fiber quality, yield, color, disease resistance, abscission) can be isolated and use to genetically engineer novel cotton varieties which will increase the competitiveness, long range improvement, and sustainability of U.S. agriculture.