| Compared with qualitative disease resistance conferred by disease resistance (R) genes, quantitative disease resistance conferred by quantitative trait loci (QTL) is presumably of wider spectrum and durable. The objectives of this study were (1) to determine the chromosomal locations of a number of defense-responsive genes and to examine the relationship between these genes and disease resistance QTL, (2) to isolate WRKY-type genes from rice. It is believed that location correspondence between defense-responsive genes and resistance QTL will provide the starting point for characterizing these genes and the functional study of WRKY-type genes will be significant to get an insight in the mechanism of disease resistance in rice.Forty-four cDNA clones, representing 44 defense-responsive genes, were fine mapped to 56 loci distributed on 9 of the 12 rice chromosomes. The locations of 32 loci detected by 27 cDNA clones were associated with previously identified resistance QTL for different rice diseases, including blast, bacterial blight, sheath blight and yellow mottle virus. The loci detected by the same multiple-copy cDNA clones were frequently located on similar locations of different chromosomes. Some of the multiple loci detected by the same clones were all associated with resistance QTL. These results suggest that some of the genes may be important components in regulation of defense responses against pathogen invasion and they may be the candidates for studying the mechanism of quantitative disease resistance in rice.The expression of cDNA sequence, El 1211, was induced by pathogen in disease resistance rice varieties. This clone was a fragment of WRKY-type transcriptional factor gene. Two genes highly homologous with WRKY-type genes were isolated from Minghui 63 and Zhenshan 97 respectively. Both of them had conserved amino acid sequence WRKYGQK and typical ZnF motif C-X5-C-X23-H-X-H of this family. Antisense strands of WRKY-type gene from Minghui 63 were transformed into RIL15, which is a line of recombinant inbred linos (RILs) of Minghui 63 and Zhenshan 97. Totally 65 TO transgenic plants were obtained. The GUS positive transgenic plant frequency was 42%. When inoculated with pathogens, 2 antisense transgenic plants, A36 and A37, showed evident enhancement in disease susceptibility in contrast with untransgenic plants. This result suggested that WRKY-type genes might play a fairly important role in regulation of disease resistance in rice. |
