The Aspartic Proteinase Family of Three Phytophthora Species

MEIJER, HJG; KAY, J; TEN HAVE A; GOVERS F; VAN KAN JAL

Asilomar

Conferencia; 26th Fungal Genetics Conference; 2011

Background: Phytophthora species are oomycete plant pathogens with such major social and economic impactthat genome sequences have been determined for Phytophthora infestans, P. sojae and P. ramorum. Pepsin-likeaspartic proteinases (APs) are produced in a wide variety of species (from bacteria to humans) and containconserved motifs and landmark residues. APs fulfil critical roles in infectious organisms and their host cells.Annotation of Phytophthora APs would provide invaluable information for studies into their roles in the physiologyof Phytophthora species and interactions with their hosts.Results: Genomes of Phytophthora infestans, P. sojae and P. ramorum contain 11-12 genes encoding APs. Nine ofthe original gene models in the P. infestans database and several in P. sojae and P. ramorum (three and four,respectively) were erroneous. Gene models were corrected on the basis of EST data, consistent positioning ofintrons between orthologues and conservation of hallmark motifs. Phylogenetic analysis resolved the PhytophthoraAPs into 5 clades. Of the 12 sub-families, several contained an unconventional architecture, as they either lacked asignal peptide or a propart region. Remarkably, almost all APs are predicted to be membrane-bound.Conclusions: One of the twelve Phytophthora APs is an unprecedented fusion protein with a putative G-proteincoupled receptor as the C-terminal partner. The others appear to be related to well-documented enzymes fromother species, including a vacuolar enzyme that is encoded in every fungal genome sequenced to date.Unexpectedly, however, the oomycetes were found to have both active and probably-inactive forms of an APsimilar to vertebrate BACE, the enzyme responsible for initiating the processing cascade that generates the Abpeptide central to Alzheimer?s Disease. The oomycetes also encode enzymes similar to plasmepsin V, a membraneboundAP that cleaves effector proteins of the malaria parasite Plasmodium falciparum during their translocationinto the host red blood cell. Since the translocation of Phytophthora effector proteins is currently a topic of intenseresearch activity, the identification in Phytophthora of potential functional homologues of plasmepsin V wouldappear worthy of investigation. Indeed, elucidation of the physiological roles of the APs identified here offers areasfor future study. The significant revision of gene models and detailed annotation presented here shouldsignificantly facilitate experimental design.