The race-specific resistance gene Pi-ta has been effectively used to control blast disease, one of the most destructive plant diseases worldwide. A single amino acid change at the 918 position of the Pi-ta protein was known to determine resistance specificity. To understand the evolutionary dynamics present, we examined sequences of the Pi-ta locus and its flanking regions in 159 accessions composed of seven AA genome Oryza species: O. sativa , O. rufipogon , O. nivara , O. meridionalis , O. glaberrima , O. barthii , and O. glumaepatula . A 3364-bp fragment encoding a predicted transposon was found in the proximity of the Pi-ta promoter region associated with the resistance phenotype. Haplotype network analysis with 33 newly identified Pi-ta haplotypes and 18 newly identified Pi-ta protein variants demonstrated the evolutionary relationships of Pi-ta haplotypes between O. sativa and O. rufipogon . In O. rufipogon , the recent directional selection was found in the Pi-ta region, while significant deviation from neutral evolution was not found in all O. sativa groups. Results of sequence variation in flanking regions around Pi-ta in O. sativa suggest that the size of the resistant Pi-ta introgressed block was at least 5.4 Mb in all elite resistant cultivars but not in the cultivars without Pi-ta . These findings demonstrate that the Pi-ta region with transposon and additional plant modifiers has evolved under an extensive selection pressure during crop breeding. Footnotes Supporting information is available online at http://www.genetics.org/cgi/content/full/genetics.109.108266/DC1 . Sequence data from this article have been deposited with the EMBL/GenBank Data Libraries under accessions nos. GQ918334 – GQ918489 and GQ984160 . ↵ 1 Present address: Samuel Roberts Noble Foundation, 2510 Sam Noble Pky., Ardmore, OK 73401. Communicating editor: J. A. B irchler Received August 6, 2009. Accepted October 3, 2009. Copyright © 2009 by the Genetics Society of America
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