Submitted to: Proceedings of the Oomycete Molecular Genetics Network
Publication Type: Abstract Only
Publication Acceptance Date: 2/19/2006
Publication Date: 5/1/2006
Citation: Grunwald, N.J., Press, C.M., Carrington, J.C. 2006. Cloning of candidate micrornas from phytophthora sojae and p. ramorum. p. 12.
Technical Abstract: A microRNA (miRNA) is a 21-24 nucleotide RNA product of a non-protein-coding gene. miRNAs are the most abundant small RNAs and have to date been described in the animal and plant kingdoms but not for the Stramenopiles. The biogenesis of miRNAs in plants is similar to that in animals in that miRNAs are processed from primary precursors by at least two steps mediated by RNAse II-like enzymes and that the miRNAs are incorporated into a protein complex (RISC). Homologs of argonaute and dicer-like proteins, involved in miRNA processing in plants, were found in both the P. sojae and P. ramorum genomes. We thus wanted to test the hypothesis that miRNAs exist in Phytophthora given that homologs of the miRNA processing machinery were apparently present. To that effect, we conducted a pilot experiment and cloned and sequenced small (18-25bp) candidate RNAs and sequenced 50 clones each from Phytophthora ramorum and P. sojae. Of the 100 clones sequenced we obtained 7 P. sojae and 14 P. ramorum candidate miRNAs. Of these, one clone resembled a miRNA based on (1) its adequate clone length of 21-24 bp, (2) a genomic sequence flanking the miRNA that contains highly complementary 20- to 30-nt segments, which is required to form the pre-miRNA hairpin structure, and (3) a pre-miRNA sequence that is conserved in the closely related species P. infestans and P. sojae. The loop sequence and sequences flanking the stem are much more variable than the miRNA sequence, which is highly conserved among Phytophthora sequences. The function of the transcript containing the putative miRNA sequence is not known. Further cloning and sequencing efforts are underway.