Xa3, conferring resistance for rice bacterial blight and encoding a receptor kinase-like protein, is the same as Xa26

Abstract

Xa3-mediated resistance for rice bacterial blight, one of the most devastating rice diseases worldwide, is influenced by genetic background. Xa3 is genetically tightly linked to Xa26, another gene for bacterial blight resistance. Xa26 belongs to a clustered multigene family encoding leucine-rich repeat (LRR) receptor kinase-like proteins. To characterize Xa3, we fine mapped it using a population segregating for only one resistance gene and markers developed from Xa26 family. Genetic analysis showed that Xa3 co-segregated with the marker of Xa26 gene and segregated from the markers of other members of Xa26 family. DNA fingerprinting revealed that rice line IRBB3 carrying Xa3 had the same copy numbers of Xa26 family members as rice line Minghui 63 carrying Xa26. Phenotypic comparison showed that all the rice lines carrying either Xa3 or Xa26 developed dark brown deposition at the border between the lesion caused by incompatible-pathogen infection and health leaf tissue, while other rice lines did not show this dark brown deposition in either incompatible or compatible interactions. These results suggest that Xa3 and Xa26 is the same gene. We name it Xa3/Xa26 to indicate the relationship between the two gene symbols. The putative encoding products of Xa3/Xa26 and its susceptible allele xa3/xa26 shared 92% sequence identity. The sequence difference occurred in the LRR domains, specifically at the solvent-exposed amino acid residues, might be the major cause that differentiates the resistant and susceptible proteins.

The Expression Pattern of a Rice Disease Resistance Gene Xa3/Xa26 Is Differentially Regulated by the Genetic Backgrounds and Developmental Stages That Influence Its Function

“…In addition to Minghui 63, the indica line IRBB3 also carries the Xa3 gene Xiang et al 2006). Transgenic lines Rb1, Rb49, and Rb17-2, carrying one copy of Xa3 driven by a native promoter in the genetic background of japonica Mudanjiang 8, showed enhanced resistance compared with the native rice lines carrying Xa3 .…”

“…Another indica rice line IRBB3 is well known to carry only one R gene, Xa3, for Xoo resistance (Ogawa et al 1991). Our studies have demonstrated that Xa3 and Xa26 are the same gene, with identical sequences in the coding region and only one nucleotide substitution occurring at 475 bp upstream of the translation initiation site Xiang et al 2006). Thus this gene is named Xa3.…”

A Rice Kinase-Protein Interaction Map

“…The additional rice members are thought to result from recent lineage-specific expansions of resistance/ defense-related genes Dardick and Ronald, 2006). Part of the support for this hypothesis comes from the fact that three cloned rice disease resistance genes, Xa21, Xa3/Xa26, and Pi-d2, encode RLKs (Song et al, 1995;Sun et al, 2004;Chen et al, 2006;Xiang et al, 2006). It has been recognized that these three resistance proteins fall into the non-RD class of kinases, which lack the conserved arginine in kinase subdomain VI.…”

Two Different Transcripts of a LAMMER Kinase Gene Play Opposite Roles in Disease Resistance

“…Minghui 63 is resistant to Xoo by both qualitative resistance, conferred by MR genes Xa3/Xa26 and xa25, and quantitative resistance, conferred by resistance QTLs (Sun et al, 2004;Xiang et al, 2006;Hu et al, 2008;Liu et al, 2011). A recombinant inbred line segregation population developed from a cross between susceptible Zhenshan 97 and Minghui 63 has been used to study quantitative disease resistance against Xoo, and several defense-responsive genes contributing to resistance QTLs have been characterized by using this population (Qiu et al, 2007;Ding et al, 2008;Hu et al, 2008;Deng et al, 2012).…”