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Title: GENOME ORGANIZATION OF MAGNAPORTHE GRISEA: INTEGRATION OF GENETIC MAPS, CLUSTERING OF TRANSPOSABLE ELEMENTS AND IDENTIFICATION OF GENOME DUPLICATIONS AND REARRANGEMENTS

Author
item NAOTO, NITTA - UNIVERSITY OF WISCONSIN
item FARMAN, MARK - UNIVERSITY OF WISCONSIN
item Leong, Sally

Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: How microbes control iron uptake is essential to their longterm survival as iron is both an essential trace element, while at the same time being toxic if taken up in excess quantities. Ustilago maydis, the cause of corn smut disease, has proven to be an excellent model system for studying how iron regulates its own uptake. U. maydis secretes chemicals, called siderophores, that enable it to take up iron from the extracellular environment. We are studying two genes, sid1 and sid2, involved in the biosynthesis of siderophores. In addition, we have identified a protein, Urbs1, which is able to turn off these genes. We have made progress in understanding how this protein turns off genes that are involved in iron uptake. This work has significance to our understanding of how iron may control the outcome of soilborne fungal diseases as a number of bacterial "biocontrol agents" appear to function by competing for iron with pathogenic fungi. This work may also lend insight on how the iron status of fungal spores may affect their viability and germinability.

Technical Abstract: A high-density genetic map of the rice blast fungus Magnaporthe grisea (Guy11 X 2539) was constructed by adding 87 cosmid-derived RFLP markers to the maps generated by Skinner et al. (1993), Smith and Leong (1993) and Farman and Leong (1995). The new map consists of 203 markers representing 132 independently segregating loci and spanning approximately 860 cM with one telomere marker unlinked. Mapping of 33 cosmid probes from the genetic map generated by Sweigard et al. (1993) has allowed integration of two M. grisea maps. The integrated map showed that the linear order of markers along all 7 chromosomes in both maps is in good agreement. Thirty of 87 markers were derived from cosmid clones that contained the retrotransposon MAGGY (Magnaporthe grisea gypsy element) (Farman et al., 1996). Mapping of single copy DNA sequences associated with the MAGGY cosmids indicated that MAGGY elements are scattered throughout the fungal genome. Most of the MAGGY cosmids also contained other classes of repetitive DNA elements suggesting that repetitive DNAs tend to cluster in the M. grisea genome. In three cases, the DNA associated with the MAGGY elements showed abnormal segregation patterns suggesting the possibility that MAGGY is involved in genomic rearrangement events. Two RFLP probes associated with MAGGY elements and one containing other repetitive DNA elements identified sequences that were duplicated only in the Guy11 genome.