Rice ESTs with disease-resistance gene- or defense-response gene-like sequences mapped to regions containing major resistance genes or QTLs.
The chromosomal locations of 109 rice expressed sequence tags (ESTs) in the rice genome were determined using a doubled haploid mapping population. These ESTs show high similarity to disease resistance genes or to defense response genes. Nine of the ESTs were mapped to three regions that contain genetically defined resistance genes on chromosomes 6 and 11. Clustering of the ESTs in the rice genome was observed at several chromosomal regions. Some of the clusters were located in regions where quantitative trait loci (QTL) associated with partial resistance to rice blast, bacterial blight and sheath blight are known to lie. Three ESTs that were mapped to the regions containing blast resistance genes Pi2 and Pia were chosen for Northern analysis after inoculation of plants with the blast fungus. Two of them, which code for a receptor-like kinase and a putative membrane channel protein, respectively, and were mapped to the Pi2 locus, were induced by rice blast infection as early as 4 h after inoculation. Transcription of another EST, which codes for a homolog of a putative human tumor suppressor and was mapped to the region containing Pia, was repressed after blast infection. These findings demonstrate that the candidate-gene approach is an efficient way of mapping resistance genes or resistance QTLs in rice.