Project description:Stress constantly challenges plant adaptation to the environment. Of all stress types, arsenic was a major threat during the early evolution of plants. The most prevalent chemical form of arsenic is arsenate, whose similarity to phosphate renders it easily incorporated into cells via the phosphate transporters. Here we found that arsenate stress provokes a notable transposon burst in plants, in coordination with arsenate/phosphate transporter repression, which immediately restricts arsenate uptake. This repression was accompanied by delocalization of the phosphate transporter from the plasma membrane. When arsenate was removed, the system rapidly restored transcriptional expression and membrane localization of the transporter. We identify WRKY6 as an arsenate-responsive transcription factor that mediates arsenate/phosphate transporter gene expression and restricts arsenate-induced transposon activation. Plants therefore have a dual WRKY-dependent signaling mechanism that modulates arsenate uptake and transposon expression, providing a coordinated strategy for arsenate tolerance and transposon gene silencing.
Project description:Melioribacter roseus is one of two cultured representatives of the phylum Ignavibacteriae. It could grow by fermentation of sugars and peptides, by aerobic respiration or by dissimilatory reduction of arsenate, nitrite or Fe(III) on fermentable and non-fermentable substrates, what allows this bacterium to adapt to fluctuating environmental conditions. Primary genome analysis highlighted key determinants of electron transport chains, providing important insights into the ability of M. roseus to use a range of electron acceptors. Complete set of genes for proton-translocating membrane complexes I and II, alternative complex III (ACIII) and seven terminal oxidoreductases was found in the M. roseus genome. Among those three different cytochrome oxidases and two different molybdopterin oxidoreductases have been proposed to determine two most active respiratory processes performed by M. roseus – aerobic respiration and dissimilatory arsenate reduction, respectively.
Project description:ABSTRACT: Inorganic arsenic is a carcinogen and its ingestion in foods such as rice presents a significant risk to human health. Plants chemically reduce arsenate to arsenite. Using genome-wide association (GWA) mapping of loci controlling natural variation in arsenic accumulation in Arabidopsis thaliana allowed us to identify the arsenate reductase required for this reduction, which we named High Arsenic Content1 (HAC1). Complementation verified the identity of HAC1, and expression in Escherichia coli lacking a functional arsenate reductase confirmed the arsenate reductase activity of HAC1. The HAC1 protein accumulates in the epidermis, the outer cell layer of the root, and also in the pericycle cells surrounding the central vascular tissue. Plants lacking HAC1 lose their ability to efflux arsenite from roots, leading to both increased transport of arsenic into the central vascular tissue and on into the shoot. HAC1 therefore functions to reduce arsenate to arsenite in the outer cell layer of the root, facilitating efflux of arsenic as arsenite back into the soil to limit its accumulation in the root and transport to the shoot. Arsenate reduction by HAC1 in the pericycle may play a role in limiting arsenic loading into the xylem. Loss of HAC1 encoded arsenic reduction leads to a significant increase in arsenic accumulation in shoots causing an increased sensitivity to arsenate toxicity. We also confirmed the previous observation that the ACR2 arsenate reductase in A. thaliana plays no detectable role in arsenic metabolism. Further, ACR2 does not interact epistatically with HAC1, since arsenic metabolism in the acr2 hac1 double mutant is disrupted in an identical manner to that described for the hac1 single mutant. Our identification of HAC1 and its associated natural variation provides an important new resource for the development of low arsenic containing food stuffs such as rice.