The Pi-ta gene in rice confers resistance to races of Magnaporthe
oryzae that contain AVR-Pita. Pi-ta encodes a predicted cytoplasmic
receptor protein with a nucleotide-binding site and a leucine-rich domain.
A panel of 51 Oryza accessions of AA genome species Oryza sativa, O.
glaberrima, O. rufipogon, O. nivara, and O. barthii, and CC genome
species O. officinalis were sequenced to investigate the diversity present
in the exon and intron regions of the Pi-ta gene. Two major clades were
identified, consisting of 16 different sequences with numerous insertion
and deletions. Only one Pi-ta resistance allele was identified despite DNA
sequences revealing 16 Pi-ta variants. Most differences were identified in
the intron region, and obvious selection of any motif was not observed in
the coding region of Pi-ta variants. Reverse-transcription polymerase
chain reaction analysis of seedlings revealed that all Pi-ta variants were
expressed with or without pathogen inoculation. The 15 Pi-ta variants can
be translated into nine proteins highly similar to the Pi-ta protein.
Resistance to M. oryzae expressing AVR-Pita correlates with alanine and
susceptibility correlates with serine at position 918 of Pi-ta in most
accessions examined. These data confirm that a single amino acid controlling
resistance specificity underlies the evolution of resistance of Pi-ta
genes in rice