Abstract
Oomycetes are a family of eukaryotic microbes that superficially resemble fungi, but which are phylogenetically distinct from them. These organisms cause major global economic losses to agriculture and fisheries, with representative pathogens being Phytophthora infestans, the cause of late potato blight and Saprolegnia diclina, the instigator of “cotton molds” in fish. As in all eukaryotes, cytoplasmic Ca2+ is a key second messenger in oomycetes, regulating life-cycle transitions, controlling motility and chemotaxis and, in excess, leading to cell-death. Despite this, little is known about the molecular mechanisms regulating cytoplasmic Ca2+ concentrations in these organisms. Consequently, this review analyzed the presence of candidate calcium channels encoded within the nine oomycete genomes that are currently available. This revealed key differences between oomycetes and other eukaryotes, in particular the expansion and loss of different channel families, and the presence of a phylum-specific group of proteins, termed the polycystic kidney disease tandem ryanodine receptor domain (PKDRR) channels.
Highlights
Oomycetes are a family of eukaryotic microbes that superficially resemble fungi, but which are phylogenetically distinct from them
As is the case with most other eukaryotes, oomycetes contain multiple organelles that are potentially capable of storing and releasing Ca2+, including the endoplasmic reticulum (ER), Golgi apparatus, lysosomes, vesicles, and mitochondria (Chapman and Vujicic, 1965). They bear candidate Ca2+ handling organelles that are found within a narrower range of eukaryotic taxa, such as the vacuolar reticulum detected in the hyphal tips of various oomycetes including Saprolegnia ferax (Allaway et al, 1997), and the zoospore peripheral vesicles of Phytophthora palmivora (Irving et al, 1984)
In S. ferax, calciumsensitive microelectrodes have been used to detect a gradient of cytoplasmic Ca2+ within hyphae, with fluxes of this ion being greatest within 8 μm of the growing tip (Lew, 1999)
Summary
Oomycetes are eukaryotic microbes that superficially resemble fungi, both in terms of their appearance and in the ecological niches which they occupy (Judelson, 2012). Along with many other parasitic members, oomycete pathogens inflict multi-billion dollar losses per annum upon the agricultural and aquacultural sectors worldwide. Oomycetes have both vegetative and sexual lifecycles. They grow as mycelia, which upon appropriate stimulation, generate fruiting bodies called sporangia, see Figure 1A. These contain motile zoospores, whose release is triggered by specific cues and which migrate toward new hosts. Given the crucial role of zoospores in the propagation of oomycetes, mechanisms controlling the development and biology of this life-cycle stage represent potential targets for the design of novel disease management strategies (Judelson and Blanco, 2005)
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