Fine Mapping And Cloning Of The Bacterial Blight Resistance Candidate Genes Of Xa31(t) In Rice

Bacterial blight (BB) of rice is a kind of serious bacterial diseases in rice. Since it was first found at 1884 in Japan, BB has been observed in worldwide rice-planting area from the south latitude 20 degrees to north latitude 58 degrees. In China, BB occurs in every rice planting areas except Xinjiang Province. BB is caused by a kind of Gram-negative bacteria, Xanthomonas (Xanthomonas oryzae pv. Oryzae,Xoo) through the stoma or wound xylem (vascular bundle) of host rice plant to reproduce taupe and white disease spot along leaf vein turns. .Rice bacterial blight disease can cause the 20~30% loss of rice output in pop year, even up to 50% in serious occurring year.Up to now, there are at least 36 BB resistance genes, 23 dominant genes and 13 recessive genes, in rice have been identified, Wang et al. discoered a new resistance gene named Xa31(t) from ZCL, a regional rice variety from Yunnan province in southwest China. It was mapped on rice chromosome 4, between G235 and C600 the two molecular markers, and the Physical distance is 100 Kb. The aim of this research is to further make a fine map of Xa31(t) and to clone its candidate genes. The main results are as follows:1. A F2 population with 294 individual plants from a cross of ZCL×IRBB1 has been constructed. Fouty six pairs of PCR primers disigned by PrePrimer 5.0 based on sequence of Nipponbare and 9311 genomes within the mapped target gene (Xa31(t)) region on chromosome 4 are used for polymorphic analysis between the two parents of ZCL and IRBB1, and 5 pairs of polymophic PCR molecular markers has been selected. Using these 5 markers screen the 294 individual plants of the F2 population from a cross of ZCL×IRBB1. Genetic analysis are finally limiting Xa31(t) within a region of about 20 Kb.2. According to the sequence of about 20 Kb in the region of resistance gene Xa31(t) located in the Nipponbare genomics, 5 candidate genes were predicted by bioinformatics analysis. and full-length cDNAs of 2 candidate genes had been obtained from ZCL. The ORFs of two candidate genes were recombined with the expression vector pCMABIA1300, respectively and introduced into rice callus of Nipponbare and TB309 by the means of Agrobacterium-mediated transformation. A few of positive plants have been identified and the resistance analysis on these plant are being studied now.