Intralineage variation among rice pathogens of Magnaporthe grisea may be caused by the transposition of Fosbury, an LTR-containing retrotransposon
Abstract
A family of repetitive elements, called MGR586, are dispersed throughout the genome of rice pathogens of Magnaporthe grisea, and are associated with a high rate of flanking restriction site polymorphisms (J. ROMAO and J. E. HAMER. 1992. PNAS. 89:5316-5320). Analysis of these MGR586 RFLPs resolves rice pathogens into a small number of groups that contain highly similar genome structures, with minor variation (LEVY et al. 1991. Phytopathology. 83:1427-1433). This suggests that rice pathogens are organized into lineages and that members of a lineage are related by clonal descent. The evolutionary mechanisms that produce genetic lineages of the pathogen are unknown. In addition, the molecular genetic mechanisms that produce minor variation among members of a lineage are also unknown. In the process of analyzing the segregation of MGR586 sequences I fortuitously identified a polymorphism, called MGR586-P2, arising in one member of a sister spore pair from a complete tetrad. Molecular cloning and genetic analysis suggests that MGR586-P2 was created by the insertion of a novel, Gypsy class retrotransposon called fosbury into DNA sequences adjacent to this MGR586 repeat. Furthermore, the strain harboring this polymorphism was found to contain a heterogeneous population of nuclei consisting of at least three different allelic forms of this chromosomal locus. My results suggest ways in which minor variation is produced within a lineage in the absence of a sexual cycle. Furthermore my results show that although M. grisea cells are uninuclear, strains are capable of existing with heterogeneous populations of nuclei, allowing novel genotypes to be produced upon sporulation.
Degree
Ph.D.
Advisors
Hamer, Purdue University.
Subject Area
Genetics|Molecular biology
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