High Resolution Mapping of the Indica-Derived Rice Blast Resistance Genes II. Pi-ta² and Pi-ta and a Consideration of Their Origin

Abstract

The indica-derived rice blast resistance genes Pi-ta2 and Pi-ta, introgressed into a japonica background, were mapped on the middle of chromosome 12 with restriction fragment length polymorphism (RFLP)/random amplified polymorphic DNA (RAPD) markers and several nearly isogenic lines (NILs). Pi-ta2 cosegregated with XNpb 289 and 196, and was flanked by closely linked markers at 0.3 (ta2-1) and 0.7 cM (XNpb 088, 319/079) on the left (up) side, and at 0.3 (RUBss) and 0.7 cM (XNpb316) on the right (down) side of the map, in F2 analyses of Pi No. 4 × japonica crosses, with 160 recessive homozygotic individuals corresponding to 320 chromosomes. CHEF (contour-clamped hexagonal electric field) Southern blotting suggested that XNpb088 and XNpb239-1, both very close to Pi-ta2, were spanned by a 170-kb band, suggesting about 500 to 750 kb/cM as the physical/genetic distances ratio in the crosses of Pi No. 4 × japonica, which was rather low in recombination ratio, in this region. Pi-ta was mapped to the position overlapping Pi-ta2 by graphical genotype analysis of an NIL with a very narrow introgressed region, Shimokita. This result suggested that these functionally related genes are allelic or at least very closely located, and that they may be derived from a common ancestral gene. However, RFLP analyses of the NILs of these two genes indicated that they are derived from rather different genomes, refuting the report that NILs of Pi-ta share a common donor with those of Pi-ta2. This indicates that the two genes differentiated at a rather ancient time. Two other pedigrees, describing spontaneous recent origins of Pi-ta in japonica, were also refuted and a single indica origin of the gene was indicated.

Evolutionary Dynamics of the Genomic Region Around the Blast Resistance Gene Pi-ta in AA Genome Oryza Species

“…First, other blast R genes in the Pi-ta region also introgressed into diverse elite rice cultivars. Other R genes such as Pi-ta 2 , Pi39, and Pi20(t) (Rybka et al 1997;Liu et al 2007;Li et al 2008) were also mapped at the Pi-ta region, but it was unknown if these and/or other unknown R genes were clustered in the Pi-ta region that have been introgressed as a large linkage block. Second, other components for the Pi-tamediated resistance reside within the 5-Mb region to form a superlocus.…”

“…The landraces Tadukan and Tetep, containing Pi-ta and other blast R genes in chromosome 12, have been used as breeding parents for preventing blast disease worldwide. Tadukan was confirmed to be the Pita donor for various Asian japonica cultivars (Rybka et al 1997) whereas Tetep was the Pi-ta donor for the U. S. cultivars (Gravois et al 1995;Moldenhauer et al 1998;McClung et al 1999;Gibbons et al 2006;Moldenhauer et al 2007). Recently, the large introgressed chromosomal segments surrounding the Pi-ta locus were identified in backcross BC 5 progenies and elite rice cultivars ( Jia 2009).…”

Two Adjacent Nucleotide-Binding Site–Leucine-Rich Repeat Class Genes Are Required to Confer Pikm-Specific Rice Blast Resistance

“…In addition, analysis of sequences at the Pi9 locus in a group of genetically distinct cultivars has revealed the complex and divergent genome organization of this locus (Zhou et al 2007). Two blast resistance genes, Pita and Pita2, have been located at the Pita locus on chromosome 12 (Kiyosawa 1967;Rybka et al 1997;Bryan et al 2000). These two genes are interesting in terms of their resistance specificity: Pita2 has a broader resistance spectrum than Pita.…”

The Broad-Spectrum Blast Resistance Gene Pi9 Encodes a Nucleotide-Binding Site–Leucine-Rich Repeat Protein and Is a Member of a Multigene Family in Rice

“…For example, 5 blast R genes have been identified at the Pi-k locus of chromosome 11 (Kiyosawa 1989;Inukai et al 1994). Pi-ta and Pi-ta 2 are allelic or at least very close to each other in the centromere region of chromosome 12 (Rybka et al 1997), while Pi5(t) and Pi3(t) map at the same location on rice chromosome 5 (Inukai et al 1996;Jeon et al 2003). To date, only 2 blast R genes, Pib (Wang et al 1999) and Pi-ta , have been cloned.…”