Genome-wide analysis of defense-responsive genes in bacterial blight resistance of rice mediated by the recessive R gene xa13

Abstract

Defense responses triggered by dominant and recessive disease resistance (R) genes are presumed to be regulated by different molecular mechanisms. In order to characterize the genes activated in defense responses against bacterial blight mediated by the recessive R gene xa13, two pathogen-induced subtraction cDNA libraries were constructed using the resistant rice line IRBB13--which carries xa13--and its susceptible, near-isogenic, parental line IR24. Clustering analysis of expressed sequence tags (ESTs) identified 702 unique expressed sequences as being involved in the defense responses triggered by xa13; 16% of these are new rice ESTs. These sequences define 702 genes, putatively encoding a wide range of products, including defense-responsive genes commonly involved in different host-pathogen interactions, genes that have not previously been reported to be associated with pathogen-induced defense responses, and genes (38%) with no homology to previously described functional genes. In addition, R-like genes putatively encoding nucleotide-binding site/leucine rich repeat (NBS-LRR) and LRR receptor kinase proteins were observed to be induced in the disease resistance activated by xa13. A total of 568 defense-responsive ESTs were mapped to 588 loci on the rice molecular linkage map through bioinformatic analysis. About 48% of the mapped ESTs co-localized with quantitative trait loci (QTLs) for resistance to various rice diseases, including bacterial blight, rice blast, sheath blight and yellow mottle virus. Furthermore, some defense-responsive sequences were conserved at similar locations on different chromosomes. These results reveal the complexity of xa13-mediated resistance. The information obtained in this study provides a large source of candidate genes for understanding the molecular bases of defense responses activated by recessive R genes and of quantitative disease resistance.

Few Mendelian Genes Underlie the Quantitative Response of a Forest Tree, Eucalyptus globulus, to a Natural Fungal Epidemic

“…This hypothesis is consistent with the moderate to high heritability previously reported for damage from MLD within E. globulus (narrow-sense heritability ¼ 0.12-0.60; Dungey et al 1997;Milgate et al 2005b). However, the possibility that the regions with QTL of large effect represent clusters of closely linked genes cannot be dismissed since resistance genes are commonly clustered in plants (Wang et al 2001;Chu et al 2004;Mondragon-Palomino and Gaut 2005). Due to the lack of QTL studies for disease resistance in Eucalyptus, comparative mapping is not possible.…”

Os8N3 is a host disease-susceptibility gene for bacterial blight of rice

“…Here, we used a previously discovered variant of avrXa7 (avrXa7-sacB50) that elicits resistance in IR24 and derived near-isogenic lines to compare the PXO99 A reaction to a typical HR on rice (22). Gene-profiling experiments with xa13 have also noted atypical defense gene expression profiles in IRBB13 plants after challenge with incompatible bacteria (25). Here, we demonstrated that the defense-related peroxidase gene PXO22.3 was not elevated in IRBB13 after challenge with PXO99 A .…”

Mitogen-activated protein kinase OsMPK6 negatively regulates rice disease resistance to bacterial pathogens

“…RNA was extracted and 20 g of total RNA was used for RNA gel blot analysis as described previously (Chu et al 2004) using the same 782-bp probe as for DNA gel blot analysis. The other hybridization probes were cDNA clones BI145L12 (GenBank accession no.…”