Comparative structural and functional analysis of genes encoding pectin methylesterases in Phytophthora spp.

• Phytophthora spp. genomes contain multiple PME-coding genes.
• PME-coding genes in Phytophthora spp. are monophyletic.
• Most P. infestans putative PME genes appear to be up-regulated during infection.
• Potential regulatory motifs exist upstream from the translational start site.

We have scanned the Phytophthora infestans, P. ramorum, and P. sojae genomes for the presence of putative pectin methylesterase genes and conducted a sequence analysis of all gene models found. We also searched for potential regulatory motifs in the promoter region of the proposed P. infestans models, and investigated the gene expression levels throughout the course of P. infestans infection on potato plants, using in planta and detached leaf assays. We found that genes located on contiguous chromosomal regions contain similar motifs in the promoter region, indicating the possibility of a shared regulatory mechanism. Results of our investigations also suggest that, during the pathogenicity process, the expression levels of some of the analyzed genes vary considerably when compared to basal expression observed in in vitro cultures of non-sporulating mycelium. These results were observed both in planta and in detached leaf assays.