Plant Genome IV Conference Plant Genome IV Conference
Libraries of high molecular weight (HMW) DNA inserts prepared in bacterial (BAC) or yeast (YAC) artificial chromosome vectors offer many advantages for the physical analysis of large genomes and for the map-based cloning of genes of interest. Common bean (Phaseolus vulgaris) is an important staple crop in many developing countries and genome analysis will lead to practical applications. In addition common bean could be proposed as an excellent model system for physical genome analysis of the legumes in general. We are currently developing a BAC library for the common bean since one goal of our group is the high density mapping and eventual map-based cloning of fungal disease resistance genes from this species. P. vulgaris is a good candidate for the successful preparation of a representative HMW BAC library due to small genome size (637 Mbp / 1C) and short life cycle. Both YAC and BAC vectors are being used since both systems offer specific advantages and disadvantages, however greater success has so far been obtained using the BAC system. Nuclear DNA from bean line A193 (of Andean origin) was cloned into vectors developed by Shizuya et al (1992, PNAS., 89:8794-8797) using the methodology of Woo et al ( 1994, Nuc. Acids Res., 22:4922-4931). To date around 3000 clones have been obtained with inserts ranging in size from 50 to 150 Kbp. These clones are currently being analyzed to determine the proportion of single/multi copy and chloroplast sequences present in this preliminary library.