Organization of chromosome ends in the rice blast fungus, Magnaporthe oryzae.
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 approximately 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.
Rehmeyer
Cathryn
C
Department of Plant Pathology, University of Kentucky, Lexington, KY 40546 USA.
Li
Weixi
W
Kusaba
Motoaki
M
Kim
Yun-Sik
YS
Brown
Doug
D
Staben
Chuck
C
Dean
Ralph
R
Farman
Mark
M
D000251:Adenosine Triphosphatases / Q000235:genetics; D001483:Base Sequence; D015825:Chromosomes, Fungal / Q000737:chemistry*; D004265:DNA Helicases / Q000235:genetics; D004251:DNA Transposable Elements; D005656:Fungal Proteins / Q000235:genetics; D020440:Gene Duplication; D005800:Genes, Fungal; D020082:Magnaporthe / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D012275:Oryza / Q000382:microbiology; D053484:RecQ Helicases; D017422:Sequence Analysis, DNA; D016615:Telomere / Q000737:chemistry*; D009626:Terminology as Topic
D004251:DNA Transposable Elements; D005656:Fungal Proteins; D000251:Adenosine Triphosphatases; D004265:DNA Helicases; D053484:RecQ Helicases