Nucleic Acids Research Advance Access published online on September 8, 2006
Nucleic Acids Research, doi:10.1093/nar/gkl588
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© 2006 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Genomics |
Organization of chromosome ends in the rice blast fungus, Magnaporthe oryzae
1 Department of Plant Pathology, University of Kentucky Lexington, KY 40546 USA 2 Department of Biology, University of Kentucky Lexington, KY 40546 USA 3 Center for Integrated Fungal Research, North Carolina State University Raleigh, NC 27695 USA
*To whom correspondence should be addressed. Tel: 859 257 7445, ext. 80728; Fax: 859 323 1961; Email: farman{at}uky.edu
Received April 11, 2006. Revised July 29, 2006. Accepted July 30, 2006.
Eukaryotic pathogens of humans often evade the immune system by switching the expression of surface proteins encoded by subtelomeric gene families. To determine if plant pathogenic fungi use a similar mechanism to avoid host defenses, we sequenced the 14 chromosome ends of the rice blast pathogen, Magnaporthe oryzae. One telomere is directly joined to ribosomal RNA-encoding genes, at the end of the 
2 Mb rDNA array. Two are attached to chromosome-unique sequences, and the remainder adjoin a distinct subtelomere region, consisting of a telomere-linked RecQ-helicase (TLH) gene flanked by several blocks of tandem repeats. Unlike other microbes, M.oryzae exhibits very little gene amplification in the subtelomere regions—out of 261 predicted genes found within 100 kb of the telomeres, only four were present at more than one chromosome end. Therefore, it seems unlikely that M.oryzae uses switching mechanisms to evade host defenses. Instead, the M.oryzae telomeres have undergone frequent terminal truncation, and there is evidence of extensive ectopic recombination among transposons in these regions. We propose that the M.oryzae chromosome termini play more subtle roles in host adaptation by promoting the loss of terminally-positioned genes that tend to trigger host defenses.
Present addresses: Cathryn Rehmeyer, Pikeville College School of Osteopathic Medicine, Pikeville, KY 41501, USA
Motoaki Kusaba, Faculty of Agriculture, Saga University, Saga, Japan
Yun-Sik Kim, Department of Plant Medicine, Chungbuk National University, Cheongju, Chungbuk, 361-763, Republic of Korea
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