INSERTIONS AND G-C RICH DNA-SEQUENCES IN THE MITOCHONDRIAL LARGE RIBOSOMAL-SUBUNIT OF LEPTOSPHAERIA-MACULANS

A portion of domain V of the mitochondrial large ribosomal DNA was seq uenced from isolates of the highly and weakly virulent pathotypes of L eptosphaeria maculans. The domain V sequence was conserved between iso lates of L. maculans, and between L. maculans and other fungi. An inse rt within the sequenced domain V region was observed in the same locat ion as those in Aspergillus nidulans, Neurospora crassa and Saccharomy ces cerevisiae. Highly virulent isolates had a 270 bp insert and weakl y virulent isolates had a 319 bp insert which are the longest inserts yet observed for fungi in domain V. The 270 and 319 bp inserts have di fferent potential effects on the secondary structure of the ribosomal RNA. Most of the insert sequence was highly homologous (90%) between p athotypes indicating that they are closely related, but the insert of the weakly virulent pathotype was longer due to an additional 49 bp at the 3' end of the insert. The 49 bp region contained a repetitive 7 b p sequence and had a higher GC-content than the rest of the insert. Th e presence of 49 bp region demonstrates that the pathotypes are distin ct, and provides insights into the evolutionary relationship between t he pathotypes of L. maculans.