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Why are Phytophthora and Other Oomycota not True Fungi?

Outlooks on Pest Management 10/2006; 17(5). DOI: 10.1564/17oct08
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    • "It remains unclear whether pathogen PCD, especially apoptosis, is involved in development of pathogenicity. Many economically important eukaryotic plant pathogens, such as Phytophthora sojae, belong to the oomycetes, which are distinct from fungi and classified in the kingdom Stramenopiles , although exhibiting many morphological and physiological similarities to fungi attributable to convergent evolution (Rossman and Palm 2006). Phytophthora plant pathogens attack a wide variety of plants, causing great losses in agriculture, forestry, and natural ecosystems worldwide (Erwin and Ribiero 1996). "
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    ABSTRACT: During pathogenic interactions, both the host and pathogen are exposed to conditions that induce programmed cell death (PCD). Certain aspects of PCD have been recently examined in eukaryotic microbes, but not in oomycetes. Here, we identified conserved TatD proteins in Phytophthora sojae; the proteins are key components of DNA degradation in apoptosis. We selected PsTatD4 for further investigation because the enzyme is unique to the oomycete branch of the phylogenetic tree. The purified protein exhibited DNase activity in vitro. Its expression was upregulated in sporangia and later infective stages, but downregulated in cysts and during early infection. Functional analysis revealed that the gene was required for sporulation and zoospore production, and the expression levels were associated with the numbers of H2O2-induced TUNEL-positive cells. Furthermore, overexpression of PsTatD4 gene reduced the virulence in a susceptible soybean cultivar. Together, these data suggest that apoptosis may play different roles in the early and late infective stages of P. sojae, and that PsTatD4 is a key regulator of infection. The association of PsTatD4 and apoptosis will lay a fundament to understand the basic biology of apoptosis and its roles in P. sojae disease cycle.
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