Microarray Analysis of Gene Expression in Rice Treated with Probenazole, a Resistance Inducer, in Special Reference to Blast Disease

Abstract

Probenazole (3-allyloxy-1,2-benzisothiazole-1,1-dioxide, PBZ) is a chemical inducer of resistance against plant pathogens and has long been practically used for protecting rice plants against a blast fungus, Magnaporthe grisea. We have been investigating the expression profiles of rice genes in response to PBZ using cDNA microarray technique. An array composed of 1265 rice expressed sequenced tag (EST) clones from various source including shoots, calli etc. was targeted by Cy5 labeled mRNAs from PBZ treated and untreated rice plants, respectively. As a result, ten cDNA clones exhibited greater than three-fold over-expression in the PBZ treated plants compared to untreated controls. Some of these clones have identities with disease resistance, pathogenesis-related and cell maintenance/development-related genes. The enhanced gene expression was confirmed for nine out of ten clones by using Northern blot and reverse transcription-polymerase chain reaction (RT-PCR) analyses. Several clones were further tested for Northern blot analysis using total RNA from blast fungus infected rice. Under the conditions used, three out of seven clones showed enhanced level of mRNA accumulation in infected plants. This may suggest that the enhanced expression of some genes by PBZ may contribute to the disease resistance in host plants. Furthermore cDNA library was constructed using mRNAs from leaves of PBZ treated rice plants and a microarray of the randomly selected 2880 clones from the library was used for choosing clones whose expression was changed in response to PBZ. Thirty nine clones were found to change their expression levels by a factor of 3 folds after PBZ treatment. Characterization including sequencing is now underway for these clones.