Profiling the Secretome and Extracellular Proteome of the Potato Late Blight Pathogen Phytophthora infestans

Abstract

Oomycetes are filamentous organisms that cause notorious diseases, several of which have a high economic impact. Well known is Phytophthora infestans, the causal agent of potato late blight. Previously, in silico analyses of the genome and transcriptome of P. infestans resulted in the annotation of a large number of genes encoding proteins with an N-terminal signal peptide. This set is collectively referred to as the secretome and comprises proteins involved in, for example, cell wall growth and modification, proteolytic processes, and the promotion of successful invasion of plant cells. So far, proteomic profiling in oomycetes was primarily focused on subcellular, intracellular or cell wall fractions; the extracellular proteome has not been studied systematically. Here we present the first comprehensive characterization of the in vivo secretome and extracellular proteome of P. infestans. We have used mass spectrometry to analyze P. infestans proteins present in seven different growth media with mycelial cultures and this resulted in the consistent identification of over two hundred proteins. Gene ontology classification pinpointed proteins involved in cell wall modifications, pathogenesis, defense responses, and proteolytic processes. Moreover, we found members of the RXLR and CRN effector families as well as several proteins lacking an obvious signal peptide. The latter were confirmed to be bona fide extracellular proteins and this suggests that, similar to other organisms, oomycetes exploit non-conventional secretion mechanisms to transfer certain proteins to the extracellular environment. Molecular & Cellular

Delivery of cytoplasmic and apoplastic effectors from Phytophthora infestans haustoria by distinct secretion pathways

“…By contrast, histone H3 and cytoplasmic eGFP were detected only in the mycelium, indicating little or no contamination of the CF with intracellular proteins. Protein secretion from cultured P. infestans hyphae without haustoria is well documented (Torto et al ., ; Meijer et al ., ). However, it was not possible here to observe the sites of secretion in vitro using confocal microscopy, as the fusion protein would be rapidly diluted upon secretion.…”

Genome‐wide characterization of Phytophthora infestans metabolism: a systems biology approach

“…The latter encyst on plant contact and germinate, thereby forming an appressorium at the tip, from which a penetration peg emerges that mediates entry into the epidermal cells of the host plant. Cell wall‐degrading enzymes are secreted that may facilitate the penetration process (Brouwer et al ., ; Meijer et al ., ). After penetration, hyphae colonize the mesophyll, where they grow intracellularly and form haustoria inside the host cells (Whisson et al ., ).…”

Molecular Profiling of the Phytophthora plurivora Secretome: A Step towards Understanding the Cross-Talk between Plant Pathogenic Oomycetes and Their Hosts

“…Both BBEs and α-CAs oxidoreductases are likely involved in pathogen detoxification processes and triggering host cell death responses [28]. In a recent study, Meijer and coworkers confirmed the secretion of five berberine-like proteins in P. infestans by using a proteomic approach [62]. Although their function in Phytophthora has not been fully elucidated, it has been hypothesized that they may act as virulence factors or as protecting agents against plant counter defenses [28], [62], [63].…”