Identification of Phytophthora sojae genes upregulated during the early stage of soybean infection

To explore the molecular mechanisms that are involved in the pathogenicity of Phytophthora sojae, a suppression subtractive hybridization method was developed to screen for P. sojae genes that are differentially expressed in the early stage of Glycine max (soybean) infection. A cDNA library enriched for upregulated parasite genes was generated; of the 73 genes that were found to be upregulated, 66 are significantly similar to sequences in the P. sojae genome, and seven have no significant similarities in the databases examined. These sequences are predicted to encode proteins involved in protein biosynthesis, energy production, cell signaling, cell-wall biogenesis, and transcription regulation. Virtual Northern assay of random selected seven genes revealed that they are all highly expressed in plant infection. Reverse transcriptase polymerase chain reaction was used to further examine the expression pattern of these genes during soybean infection. These results provide an important insight into the genes expressed during P. sojae infection of soybean, which may be involved in oomycete pathogenesis.