Comparative profiling of the transcriptional response to soybean cyst nematode infection of soybean roots by deep sequencing

To gain insight into the changes in the transcriptome of soybean roots during soybean cyst nematode （SCN） infection, we conducted genome-wide gene expression profiling using serial analysis of gene expression （SAGE） combined with Solexa sequencing. More than 3 million tags were generated from the SCN-infected and uninfected roots, and 366941 and 314591 clean UniTags were obtained from SCN-infected and uninfected samples, respectively. In the SCN-infected sample, 48249 UniTags represented 18114 reference genes. In the uninfected control, 46290 UniTags represented 19323 reference genes. Comparison of tag frequencies identified 1405 genes that were expressed at greater levels in SCN-infected roots than in uninfected roots, and 1191 genes that were expressed at lower levels. Quantitative real-time PCR analyses confirmed the changes in mRNA levels observed in our sequencing analyses. A comparable number of genes were up- and down-regulated in response to nematode infection, indicating that down-regulation of some genes might be essential in the plant response to nematodes. Our SAGE results showed significant changes in expression of many unreported genes involved in nematode infection. Approximately 7% of tags mapped to the antisense strand of genes, indicating widespread antisense transcription.