Chromosome landing at the tomato Bs4 locus

Area of Science:

• Plant genetics
• Molecular biology
• Crop science

Background:

• The tomato Bs4 gene provides resistance against specific Xanthomonas campestris strains expressing the AvrBs4 avirulence protein.
• Understanding the genetic basis of plant disease resistance is vital for crop improvement.

Purpose of the Study:

• To isolate the Bs4 gene using a map-based cloning strategy.
• To perform high-resolution genetic mapping of the Bs4 locus in tomato (Lycopersicon esculentum).

Main Methods:

• Conversion of amplified fragment length polymorphism (AFLP) and restriction fragment length polymorphism (RFLP) markers to locus-specific sequence-tagged-site (STS) markers.
• Analysis of 1972 meiotic events for genetic mapping.
• Identification and characterization of tomato yeast artificial chromosome (YAC) clones containing the Bs4 gene.
• Construction of a local YAC contig using YAC end-specific markers.

Main Results:

• High-resolution genetic mapping localized the Bs4 gene within a 1.2-cM interval.
• Two YAC clones, each with ~250 kb inserts, were identified.
• The physical to genetic distance ratio at Bs4 was determined to be 280 kb/cM, indicating higher recombination rates.
• The Bs4 locus was mapped to a physical region of 250 kb, corresponding to a genetic interval of 0.9 cM.

Conclusions:

• The map-based cloning strategy successfully narrowed down the physical location of the Bs4 gene.
• The Bs4 locus is situated within a compact genomic region, facilitating its isolation.
• The study provides valuable genetic and physical mapping data for the Bs4 gene in tomato.