Many destructive diseases of plants and animals are caused by oomycetes, a group of eukaryotic pathogens important to agricultural, ornamental, and natural ecosystems. Understanding the mechanisms underlying oomycete virulence and the genomic processes by which those mechanisms rapidly evolve is essential to developing effective long-term control measures for oomycete diseases. Several common mechanisms underlying oomycete virulence, including protein toxins and cell-entering effectors, have emerged from comparing oomycetes with different genome characteristics, parasitic lifestyles, and host ranges. Oomycete genomes display a strongly bipartite organization in which conserved housekeeping genes are concentrated in syntenic gene-rich blocks, whereas virulence genes are dispersed into highly dynamic, repeat-rich regions. There is also evidence that key virulence genes have been acquired by horizontal transfer from other eukaryotic and prokaryotic species.
[Show abstract][Hide abstract] ABSTRACT: Plasmopara viticola is an oomycete pathogen that causes downy mildew, one of the most devastating diseases of grapevine. Currently, the molecular basis of the interaction between this pathogen and the grapevine host is not well understood. To explore the genes involved in P. viticola pathogenicity we performed RNA-Seq analysis of cDNAs derived from downy mildew-infected grapevine leaves for three different P. viticola isolates; two from China (JL-7-2, ZJ-1-1) and one from Australia (CSIRO-L-2). Approximately 30,000 unigenes were predicted for each of the three isolates and from these over 500 potential secreted proteins were identified. Using three prediction methods, a total of 51 PvRXLR effectors were identified to be present in the secretome, with at least 26 shared by two or more P. viticola isolates. Expression profiling, based on RNA-Seq data, indicated that PvRXLRs showed three different expression patterns during infection. Transient expression of selected PvRXLRs in Nicotiana benthamiana demonstrated that all were capable of suppressing programmed cell death triggered by the mouse BAX protein or the PAMP INF1. Additionally, BLASTP and Hidden Markov Model (HMM) searches identified 10 predicted proteins belonging to the CRN (Crinkler) group of oomycete effectors. Pfam domain analysis of the secretome also identified a diverse range of putative apoplastic effectors, the major groups being glycosyl hydrolases, peptidases and protease-inhibitors. This study provides the first detailed analysis of the secretome of grapevine downy mildew and its encoded effector arsenal.
[Show abstract][Hide abstract] ABSTRACT: SUMMARY
Oomycetes form a deep lineage of eukaryotic organisms that includes a large number of plant pathogens which threaten natural and managed ecosystems.We undertook a survey to query
the community for their ranking of plant-pathogenic oomycete species based on scientific and economic importance. In total, we received 263 votes from 62 scientists in 15 countries for a total of 33 species. The Top 10 species and their ranking are: (1) Phytophthora infestans; (2, tied) Hyaloperonospora arabidopsidis; (2, tied) Phytophthora ramorum; (4) Phytophthora sojae; (5) Phytophthora capsici; (6) Plasmopara viticola; (7) Phytophthora cinnamomi; (8, tied) Phytophthora parasitica; (8, tied) ultimum; and (10) Albugo candida. This article provides an introduction to these 10 taxa and a snapshot of current research. We hope that the list will serve as a benchmark for future trends in oomycete research.
Keywords: oomycetes plant pathology, microbiology, diversity, genomics.
"Cytoplasmic effectors, namely the RXLR and CRN, are characterized by N-terminal signal peptides with conserved motifs that are required for host translocation followed by a highly diverse C-terminal domain that confers effector biochemical activity (Schornack et al. 2009; Win et al. 2007). The RXLR effectors are defined by the conserved N-terminal RXLR-dEER motif that facilitates transport of these effectors into host cells (Haas et al. 2009; Jiang et al. 2008; Whisson et al. 2007; Win et al. 2012). This domain is functionally equivalent to the conserved N-terminal LXLFLAK motif of CRN effectors (Haas et al. 2009; Schornack et al. 2010; Win et al. 2012). "
[Show abstract][Hide abstract] ABSTRACT: Late blight, caused by Phytophthora infestans (Mont.) de Bary, is the most historically significant and economically destructive disease of potatoes (Solanum tuberosum L.). In addition to potato, P. infestans can also infect tomato and some other members of the Solanaceae, and this has contributed to the recent late blight epidemic in Canada and the United States. Propagation of P. infestans in Canada and the United States has been mainly through asexual reproduction and this has led to the development of several dominant clonal lineages. Various P. infestans markers have been developed that are invaluable in monitoring the evolution and movement of these P. infestans genotypes. Population diversity and disease incidence has increased through the development of systemic fungicide insensitivity and the transcontinental shipment of the pathogen on late blight infected potato tubers and tomato plantlets. Introduction of the P. infestans A2 mating type to several regions of Canada and the United States has also increased the opportunity for sexual reproduction and recombination, potentially contributing to greater P. infestans genetic diversity and pathogenicity. Advances in P. infestans molecular analysis have revealed a complex pathogen with a genome capable of evolving relatively quickly. Management of late blight will therefore require new, multifaceted strategies which include monitoring pathogen evolution and implementing sustainable production practices.
American Journal of Potato Research 12/2014; 91(6):579-593. DOI:10.1007/s12230-014-9401-0 · 1.20 Impact Factor
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