Physical map and organization of chromosome 7 in the rice blast fungus, Magnaporthe grisea

The rice blast fungus Magnaporthe grisea is a highly destructive plant path ogen and one of the most important for studying various aspects of host-pla nt interactions. It has been widely adopted as a model organism because it is ideally suited for genetic and biological studies. To facilitate map-bas ed cloning, chromosome walking, and genome organization studies of M. grise a, a complete physical map of chromosome 7 was constructed using a large-in sert (130 kb) bacterial artificial chromosome (BAC) library. Using 147 chro mosome 7-specific single-copy BAC clones and 20 RFLP markers on chromosome 7, 625 BAC clones were identified by hybridization. BAC clones were digeste d with HindIII, and fragments were size separated on analytical agarose gel s to create DNA fingerprints. Hybridization contigs were constructed using a random cost algorithm, whereas fingerprinting contigs were constructed us ing the software package FPC. Results from both methods were generally in a greement, but numerous anomalies were observed. The combined data produced five robust anchored contigs after gap closure by chromosomal walking. The genetic and physical maps agreed closely. The final physical map was estima ted to cover >95% of the 4.2 Mb of chromosome 7. Based on the contig maps, a minimum BAC tile containing 42 BAC clones was created, and organization o f repetitive elements and expressed genes of the chromosome was investigate d.