Evolution Converted Bacterial Arsenic Effluxers into Plant Nutrient Boron and Silicon Importers (IMAGE)
Caption
Prokaryotes possess arsenic resistance (ars) operons for arsenic (As) detoxification and export. Some bacteria possess an ars operon-located aqpN aquaporin gene, which facilitates the transmembrane diffusion of As(III) species. In prokaryotes, arsenate [As(V)] enters the cells via phosphate transporters. Transcription of arsR is induced by As(V) and the protein produced, ArsR, regulates the expression of aqpN and arsC. The chemical gradient needed to cause As efflux through AqpNs is maintained by the reduction of As(V) to As(III), catalysed by the arsenate reductase ArsC. An aqpN gene was probably transferred to charophytic algae by a horizontal gene transfer event. During evolution, this ancestral plant AQPN-type channel protein converted into the so-called Nodulin 26-like Intrinsic Proteins (NIPs) which are essential to regulate the uptake and translocation of the important nutrients silicon (Si) and boron (B) in present-day seed plants. When Si and B became beneficial and essential elements for vascular plant groups, respectively, these proteins underwent structural changes which resulted in a neo- and subfunctional-isation enabling them to form efficient B and Si transport regulators.
Credit
G.P. Bienert / IPK
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