Submitted to: Plant and Animal Genome VX Conference Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 8/26/2003
Publication Date: 8/26/2003
Citation: Chauhan, R., Durfee, T., Blattner, F., Holt, J., Leong, S.A. 2003. Exceptional haplotype divergence at a rice blast resistance locus, Pi-CO39(T) flanked by clusters of serpin genes. Plant and Animal Genome VX Conference Abstracts. p. 155.
Technical Abstract: We have genetically mapped and physically delineated the chromosomal location of a new rice blast resistance locus, designated as Pi-CO39(t) corresponding to avirulence locus, AVR1-CO39 of Magnaporthe grisea on the short arm of rice chromosome 11 (Chauhan et al., 2002). Comparative sequence analysis of blast resistant (CO39-indica) and susceptible (Nipponbare-japonica) rice genotypes at genomic regions co-segregating with Pi-CO39(t) showed that two haplotypes are substantially diverged with respect to relative number, size, orientation and location of NBS-LRR genes. A cluster of 18 NBS-LRR disease resistance-like genes in Nipponbare haplotype (500 kb) and a cluster of 8 NBS-LRR genes in the CO39 haplotype (200 kb) has been identified at the Pi-CO39(t) locus. Both the NBS-LRR gene clusters are flanked by clusters of Serpin genes (serine/cysteine proteinase-inhibitors), which have been implicated as negative regulators of Toll-mediated antifungal defense pathway in Drosophila (Levashina EA et al. 1999. Constitutive activation of toll-mediated antifungal defense in serpin-deficient Drosophila. Science 285: 1917-9). Whether these rice serpins also possess any regulatory role in blast resistance phenotype, is being investigated. All the predicted resistance genes belong to non-TIR NBS-LRR subfamily of plant disease resistance-like genes suggested to be more abundant in monocot genomes. Expression analysis of predicted disease resistance as well as serpin genes was performed on RNA templates isolated from rice leaves inoculated with Guy11 and a Guy11 AVR1-CO39 transformant and harvested at different time points (0, 3, 6, 12, 24, 36, 48, 96, 7d). All the NBS-LRR genes are constitutively expressed in both the haplotypes, except the RPR1 (NBR16) gene in Nipponbare, which showed induced expression in response to M. grisea infection. Two serpin genes in CO39 and one in Nipponbare showed induced expression in response to M. grisea infection. Functional characterization of putative R genes in CO39 haplotype is in progress both by complementation as well as gene silencing.