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. Th ese ESTs show high similarity to disease resistance genes or to defense res ponse genes. Nine of the ESTs were mapped to three regions that contain gen etically defined resistance genes on chromosomes 6 and 11. Clustering of th e 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 sh eath blight are known to lie. Three ESTs that were mapped to the:regions co ntaining blast resistance genes Pi2 and Pia were chosen for Northern analys is after inoculation of plants with the blast fungus. Two of them, which co de for a receptor-like kinase and a putative membrane,channel protein, resp ectively, and were mapped to the Pi2 locus, were induced by rice blast infe ction as early as 4 h after inoculation. Transcription of another EST, whic h codes for a homolog of a putative human tumor suppressor and was mapped t o the region containing Pin, was repressed after blast infection. These fin dings demonstrate that the candidate-gene approach is an efficient way of m apping resistance genes or resistance QTLs in rice.