Expression analyses of three members of the AtPHO1 family reveal differential interactions between signaling pathways involved in phosphate deficiency and the responses to auxin, cytokinin, and abscisic acid

The PHO1 protein is involved in loading inorganic phosphate (Pi) to the root xylem. Ten genes homologous to AtPHO1 are present in the Arabidopsis thaliana (L.) Heyn genome. From this gene family, transcript levels of only AtPHO1, AtPHO1;H1 and AtPHO1;H10 were increased by Pi-deficiency. While the up-regulation of AtPHO1;H1 and AtPHO1;H10 by Pi deficiency followed the same rapid kinetics and was dependent on the PHR1 transcription factor, phosphite only strongly suppressed the expression of AtPHO1;H1 and had a minor effect on AtPHO1;H10. Addition of sucrose was found to increase transcript levels of both AtPHO1 and AtPHO1;H1 in Pi-sufficient or Pi-deficient plants, but to suppress AtPHO1:H10 under the same conditions. Treatments of plants with auxin or cytokinin had contrasting effect depending on the gene and on the Pi status of the plants. Thus, while both hormones down-regulated expression of AtPHO1 independently of the plant Pi status, auxin and cytokinin up-regulated AtPHO1;H1 and AtPHO1;H10 expression in Pi-sufficient plants and down-regulated expression in Pi-deficient plants. Treatments with abscisic acid inhibited AtPHO1 and AtPHO1;H1 expression in both Pi-sufficient and Pi-deficient plants, but increased AtPHO1;H10 expression under the same conditions. The inhibition of expression by abscisic acid of AtPHO1 and AtPHO1;H1, and of the Pi-starvation responsive genes AtPHT1;1 and AtIPS1, was dependant on the ABI1 type 2C protein phosphatase. These results reveal that various levels of cross talk between the signal transduction pathways to Pi, sucrose and phytohormones are involved in the regulation of expression of the three AtPHO1 homologue

Evolution moléculaire de loci effecteurs et de gènes d'avirulence chez Magnaporthe oryzae, champignon pathogène de riz et d'autres Poacées : [P02/07]

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Structure and Expression Profile of the Arabidopsis PHO1 Gene Family Indicates a Broad Role in Inorganic Phosphate Homeostasis

PHO1 has been recently identified as a protein involved in the loading of inorganic phosphate into the xylem of roots in Arabidopsis. The genome of Arabidopsis contains 11 members of the PHO1 gene family. The cDNAs of all PHO1 homologs have been cloned and sequenced. All proteins have the same topology and harbor a SPX tripartite domain in the N-terminal hydrophilic portion and an EXS domain in the C-terminal hydrophobic portion. The SPX and EXS domains have been identified in yeast (Saccharomyces cerevisiae) proteins involved in either phosphate transport or sensing or in sorting proteins to endomembranes. The Arabidopsis genome contains additional proteins of unknown function containing either a SPX or an EXS domain. Phylogenetic analysis indicated that the PHO1 family is subdivided into at least three clusters. Reverse transcription-PCR revealed a broad pattern of expression in leaves, roots, stems, and flowers for most genes, although two genes are expressed exclusively in flowers. Analysis of the activity of the promoter of all PHO1 homologs using promoter-β-glucuronidase fusions revealed a predominant expression in the vascular tissues of roots, leaves, stems, or flowers. β-Glucuronidase expression is also detected for several promoters in nonvascular tissue, including hydathodes, trichomes, root tip, root cortical/epidermal cells, and pollen grains. The expression pattern of PHO1 homologs indicates a likely role of the PHO1 proteins not only in the transfer of phosphate to the vascular cylinder of various tissues but also in the acquisition of phosphate into cells, such as pollen or root epidermal/cortical cells

Iron-sulphur cluster assembly in plants: distinct NFU proteins in mitochondria and plastids from Arabidopsis thaliana.

Recent results are in favour of a role for NFU-like proteins in Fe-S cluster biogenesis. These polypeptides share a conserved CXXC motif in their NFU domain. In the present study, we have characterized Arabidopsis thaliana NFU1-5 genes. AtNFU proteins are separated into two classes. NFU4 and NFU5 are part of the mitochondrial type, presenting a structural organization similar to Saccharomyces cerevisiae Nfu1p. These proteins complement a Delta isu1 Delta nfu1 yeast mutant and NFU4 mitochondrial localization was confirmed by green fluorescent protein fusion analysis. AtNFU1-3 represent a new class of NFU proteins, unique to plants. These polypeptides are made of two NFU domains, the second having lost its CXXC motif. AtNFU1-3 proteins are more related to Synechocystis PCC6803 NFU-like proteins and are localized to plastids when fused with the green fluorescent protein. NFU2 and/or NFU3 were detected in leaf chloroplasts by immunoblotting. NFU1 and NFU2 are functional NFU capable of restoring the growth of a Delta isu1 Delta nfu1 yeast mutant, when addressed to yeast mitochondria. Furthermore, NFU2 recombinant protein is capable of binding a labile 2Fe-2S cluster in vitro. These results demonstrate the presence of distinct NFU proteins in Arabidopsis mitochondria and plastids. Such results suggest the existence of two different Fe-S assembly machineries in plant cells

A Fluxless and Low-Temperature Flip Chip Process Based on Insertion Technique

International audienceAbstract: For heterogeneous materials assembly, the thermal expansion mismatch between the chip and the substrate is a roadblock for Hip chip bonding of ultrafine-pitch (= 20 mm). Residual strains in bumps and device warpage have been calculated to evaluate the thermomechanical limits of a conventional flip chip soldering process using micro bumping. As a solution to overcome these limits, this paper describes a new patented flip-chip technology representing a technological breakthrough compared to conventional methods such as soldering or bonding through conductive adhesives. Electrical connections are performed by the insertion of metallic micro-tips in a ductile material. As a low-temperature process and fluxless technology, this method is adapted to fine-pitch and large devices. As a proof of concept, we present the bonding results obtained on fine-pitch large arrays of daisy chains with 500 x 500 contacts and 30-mu m pitch. The electrical contact has been demonstrated and characterized in terms of resistance and yield

A single amino acid change (Y318F) in the L-arabitol dehydrogenase (LadA) from Aspergillus niger results in a significant increase in affinity for D-sorbitol

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The pentose catabolic pathway of the rice-blast fungus Magnaporthe oryzae involves a novel pentose reductase restricted to few fungal species

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