Comparative analysis of expressed sequences in Phytophthora sojae

Phytophthora sojae (Kaufmann and Gerdemann) is an oomycete that causes stem and root rot on soybean (Glycine max L. Merr) plants. We have constructed three cDNA libraries using mRNA isolated from axenically grown mycelium and zoospores and from tissue isolated from plant hypocotyls 48 h after inocul ation with zoospores. A total of 3,035 expressed sequence tags (ESTs) were generated from the three cDNA libraries, representing an estimated 2,189 cD NA transcripts. The ESTs were classified according to putative function bas ed on similarity to known proteins, and were analyzed for redundancy within and among the three source libraries. Distinct expression patterns were ob served for each library. By analysis of the percentage G+C content of the E STs, we estimate that two-thirds of the ESTs from the infected plant librar y are derived from P. sojae cDNA transcripts. The ESTs originating from thi s study were also compared with a collection of Phytophthora infestans ESTs and with all other non-human ESTs to assess the similarity of the P, sojae sequences to existing EST data. This collection of cDNA libraries, ESTs, a nd accompanying annotation will provide a new resource for studies on oomyc etes and on soybean responses to pathogen challenge.