Gene expression of rice mutant lines in response to feeding by brown planthopper (Nilaparvatha lugens Stal).

This study aimed to understand the molecular mechanism of resistance (defense) in the BPH resistant cultivars by comparing the genetic makeup of the rice variants known to be resistant. Specifically, the gene expression in BPH resistant cultivars and expression patterns of genes responsible for BPH resistance were determined in IR64 (wild type) and D518 (mutant line) of rice. A mutant with a higher resistance, like D518, most likely utilizes these types of resistance genes for its resistance genotype. However, the correlated expression of common genes between IR64 and D518 suggested an involvement of BPH resistance response genes. It would be beneficial to conduct experiments to confirm significance of the resistance phenotype of the IR64 and D518. Microarray technology, a new method of bioinformatics was applied in this study. This was applied in the form of cDNA Microarray Analysis that utilized a high density rice oligo-array representing 60,000 oligo-arrays of the rice genome. The differential gene expressions were determined statistical within or between genotypes and at different time courses after BPH infestation using MAANOVA analysis. The first major scientific contribution of this study is that a total of 125 candidate genes were found to be responsible for resistance responses to BPH attack in both genotypes studied. The BPH feeding on D518 resulted in differential expression (70 genes) which included 55 genes that showed similar expression pattern in IR64; 103 genes had a known function and 22 genes had an unknown function, and those genes were listed for further study. The results showed overlaps between the responses in D518 and IR64 to BPH feeding. By using contrasting phenotypes, this study provided useful information for understanding rice-BPH interactions. The second contribution was the confirmation that the same genes are involved in producing resistance in both resistant varieties, although the comparison has shown that the number of genes expressed was not exactly the same. The common genes between IR64 and D518 in response to BPH suggested that there was a set of genes responsible for BPH resistance. Third and final major contribution is the confirmation that auxin signaling depends on the targeted protein degradation and also that the rice-BPH interaction might be associated with the auxin signaling pathway. The higher expression level in variety D518 implies that the genes of the jasmonic acid independent pathway also participate in the response of rice to the piercing /sucking insect. This work, could lead to the development of insect resistant rice varieties, which would be capable of producing their own BH repellent.