Highly variable minichromosomes and highly conserved endoglucanase genes in the phytopathogenic fungusMacrophomina phaseolina

摘要

Electrophoretic karyotype analysis of 17 different isolates ofMacrophomina phaseolinarevealed the presence of from zero to six minichromosomes (less than 2000 kilobases (kb)), with the smallest size observed being approximately 785 kb. Each isolate had a unique minichromosome pattern, whether from the same field or from different continents. The highly variable minichromosome pattern contrasts to the high degree of conservation found in the two endoglucanase genes (egl1andegl2) harbored byM. phaseolina. Gene structure was conserved, as judged by Southern analysis, and restriction fragment length was conserved. Digestion of DNA withSal1resulted in a 2-kb fragment containingegl1, and a 4-kb fragment containedegl2. Conservation of restriction fragment length suggests that the portions of the genome harboring the endoglucanases are less subject to rearrangement, relative to minichromosome DNA.Key words: charcoal rot, cell wall degrading enzymes, cellulase.