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Zinc (Zn) is essential for the optimal growth of plants but is toxic if present in excess, so Zn homeostasis needs to be finely tuned. Understanding Zn homeostasis mechanisms in plants will help in the development of innovative approaches for the phytoremediation of Zn-contaminated sites. In this study, Zn tolerance quantitative trait loci (QTL) were identified by analyzing differences in the Bay-0 and Shahdara accessions of Arabidopsis thaliana. Fine-scale mapping showed that a variant of the Fe homeostasis-related FERRIC REDUCTASE DEFECTIVE3 (FRD3) gene, which encodes a multidrug and toxin efflux (MATE) transporter, is responsible for reduced Zn tolerance in A. thaliana. Allelic variation in FRD3 revealed which amino acids are necessary for FRD3 function. In addition, the results of allele-specific expression assays in F1 individuals provide evidence for the existence of at least one putative metal-responsive cis-regulatory element. Our results suggest that FRD3 works as a multimer and is involved in loading Zn into xylem. Cross-homeostasis between Fe and Zn therefore appears to be important for Zn tolerance in A. thaliana with FRD3 acting as an essential regulator. [ABSTRACT FROM AUTHOR]

Zinc (Zn) is essential for the optimal growth of plants but is toxic if present in excess, so Zn homeostasis needs to be finely tuned. Understanding Zn homeostasis mechanisms in plants will help in the development of innovative approaches for the phytoremediation of Zn-contaminated sites. In this study, Zn tolerance quantitative trait loci (QTL) were identified by analyzing differences in the Bay-0 and Shahdara accessions of Arabidopsis thaliana. Fine-scale mapping showed that a variant of the Fe homeostasis-related FERRIC REDUCTASE DEFECTIVE3 (FRD3) gene, which encodes a multidrug and toxin efflux (MATE) transporter, is responsible for reduced Zn tolerance in A. thaliana. Allelic variation in FRD3 revealed which amino acids are necessary for FRD3 function. In addition, the results of allele-specific expression assays in F1 individuals provide evidence for the existence of at least one putative metal-responsive cis-regulatory element. Our results suggest that FRD3 works as a multimer and is involved in loading Zn into xylem. Cross-homeostasis between Fe and Zn therefore appears to be important for Zn tolerance in A. thaliana with FRD3 acting as an essential regulator. [ABSTRACT FROM AUTHOR]

Carrageenans are sulfated galactans found in the cell walls of numerous red seaweeds (Rhodophyta). They are classified according to the number and the position of sulfate ester groups and the occurrence of 3,6-anhydro-galactose. Although the carrageenan biosynthesis pathway is not fully understood, it is usually accepted that the last step consists of the formation of a 3,6-anhydro ring found in κ- and ι-carrageenans through the enzymatic conversion of D-galactose-6-sulfate or D-galactose-2,6- disulfate occurring in μ- and ν-carrageenan, respectively. We purified two enzymes, sulfurylase 1(65 kD) and sulfurylase 11(32 kD), that are able to catalyze the conversion of ν- into ι-carrageenan. We compared their sulfate release rates (i.e. arising from the formation of the anhydro ring) with the viscosity of the solution and demonstrated two distinct modes of action. In addition, we found that some mixtures of sulfurylase I and II lead to the formation of carrageenan solutions with unexpectedly low viscosities. We discuss the implication of these findings for the assembly of a densely aggregated matrix in red algal cell walls. [ABSTRACT FROM AUTHOR]

The expression of 28 high light (HL)-responsive genes of Arabidopsis was analysed in response to environmental and physiological factors known to influence the expression of the HL-responsive gene, ASCORBATE PEROXIDASE2 (APX2). Most (81%) of the HL-responsive genes, including APX2, required photosynthetic electron transport for their expression, and were responsive to abscisic acid (ABA; 68%), strengthening the impression that these two signals are crucial in the expression of HL-responsive genes. Further, from the use of mutants altered in reactive oxygen species (ROS) metabolism, it was shown that 61% of these genes, including APX2, may be responsive to chloroplast-sourced ROS. In contrast, apoplastic/plasma membrane-sourced H2O2, in part directed by the respiratory burst NADPH oxidases AtrbohD and AtrbohF, was shown to be important only for APX2 expression. APX2 expression in leaves is limited to bundle sheath parenchyma; however, for the other genes in this study, information on their tissue specificity of expression is sparse. An analysis of expression in petioles, enriched for bundle sheath tissue compared with distal leaf blade, in HL and control leaves showed that 25% of them had >10-fold higher expression in the petiole than in the leaf blade. However, this did not mean that these petiole expression genes followed a pattern of regulation observed for APX2. [ABSTRACT FROM PUBLISHER]

The metal tolerance of metal hyper-accumulating plants is a poorly understood mechanism. In order to unravel the molecular basis of zinc (Zn) tolerance in the Zn hyper-accumulating plant Arabidopsis halleri ssp. halleri, we carried out a functional screening of an A. halleri cDNA library in the yeast Saccharomyces cerevisiae to search for genes conferring Zn tolerance to yeast cells. The screening revealed four A. halleri defensin genes ( AhPDFs), which induced Zn but not cadmium (Cd) tolerance in yeast. The expression of AhPDF1.1 under the control of the 35S promoter in A. thaliana made the transgenic plants more tolerant to Zn than wild-type plants, but did not change the tolerance to Cd, copper (Cu), cobalt (Co), iron (Fe) or sodium (Na). Thus, AhPDF1.1 is able to confer Zn tolerance both to yeast and plants. In A. halleri, defensins are constitutively accumulated at a higher level in shoots than in A. thaliana. A. halleri defensin pools are Zn-responsive, both at the mRNA and protein levels. In A. thaliana, some but not all defensin genes are induced by ZnCl2 treatment, and these genes are not induced by NaCl treatment. Defensins, found in a very large number of organisms, are known to be involved in the innate immune system but have never been found to play any role in metal physiology. Our results support the proposition that defensins could be involved in Zn tolerance in A. halleri, and that a role for plant defensins in metal physiology should be considered. [ABSTRACT FROM AUTHOR]

GSK3/Shaggy kinases are involved in a wide range of fundamental processes in animal development and metabolism. In angiosperm plants, these kinases are encoded by moderate-sized gene families, which appear to have a complex set of functions. Here, we present the characterization of five members of the GSK3/Shaggy gene family in the bryophyte Physcomitrella patens. The P. patens GSK3/Shaggy kinases (PpSK) are organized in a group of closely related paralogues with respect to their gene sequence and structure. Indeed, a phylogenetic analysis of the GSK3/Shaggy kinase sequences from plants and animals showed that the five PpSK proteins are monophyletic, and closer to subgroups I and IV described in angiosperms. Expression analyses performed by quantitative real-time RT-PCR on a wide range of growing conditions showed that PpSK genes responded only to either desiccation, PEG or sorbitol. As demonstrated by both inductions of marker genes and protonemal cell plasmolyses, these treatments resulted in a hyperosmotic stress. Altogether, these data suggest that (1) GSK3/Shaggy kinase gene multiplication occurred early in plant evolution, before the separation between bryophytes and vascular plants, and (2) both gene loss and duplication occurred in the ancestor of P. patens along with functional gene diversification in angiosperms. However, conservation of the transcriptional responses between Physcomitrella and Arabidopsis suggests the identification of an ancestral response of the GSK3/Shaggy kinases genes to osmotic stress. [ABSTRACT FROM AUTHOR]

Steady-state numbers of peripheral lymphocyte are tightly controlled. For conventional T cells, signals delivered through the interaction of the T cell receptor (TCR) with antigen-loaded MHC molecules are required for the peripheral survival of naive T cells and for their homeostatic expansion in lymphopenic hosts. Cytokines, including IL-7, are also essential for survival of peripheral naive T cells. CD1d-restricted, Vα14[sup +] natural killer (NK)-T cells are a specialized autoreactive T subset with immunoregulatory activity. The relative roles of TCR engagement and cytokine signaling in the peripheral homeostasis of Vα14[sup +] NK-T cells were investigated. After adoptive transfer, the survival and expansion of peripheral Vα14[sup +] NK-T cells was independent of CD1d expression in the host. In contrast, IL-15 (but not IL-7) was required for maintenance of peripheral CD1d-reactive Vα14[sup +] T cells. Comparison of Vα14[sup +] T cell transfers into NK-proficient vs. deficient hosts suggests that NK-T cells and NK cells compete for peripheral resources. Our results indicate that IL-15 maintains the homeostasis of peripheral Vα14[sup +] NK-T cells. In contrast, TCR "tickling" of NK-T cells, if it occurs under steady-state conditions, does not by itself provide a sufficient signal for their peripheral survival. [ABSTRACT FROM AUTHOR]

Mitochondrial DNA from the unicellular rhodophyte Cyanidium caldarium RK-1 and the multicellular Chondrus crispus were isolated, cloned, and sequenced. Two genes, sdhB and sdhC, that encode subunits of the succinate dehydrogenase, were identified by similarity. These genes form a cluster ( titsdhCB) in both red algae. [ABSTRACT FROM AUTHOR]