Phosphatidylinositol 3-phosphate-binding protein AtPH1 controls the localization of the metal transporter NRAMP1 in .

"Too much of a good thing" perfectly describes the dilemma that living organisms face with metals. The tight control of metal homeostasis in cells depends on the trafficking of metal transporters between membranes of different compartments. However, the mechanisms regulating the location of transport proteins are still largely unknown.

Bypassing Iron Storage in Endodermal Vacuoles Rescues the Iron Mobilization Defect in the natural resistance associated-macrophage protein3natural resistance associated-macrophage protein4 Double Mutant.

To improve seed iron (Fe) content and bioavailability, it is crucial to decipher the mechanisms that control Fe storage during seed development. In Arabidopsis (Arabidopsis thaliana) seeds, most Fe is concentrated in insoluble precipitates, with phytate in the vacuoles of cells surrounding the vasculature of the embryo. NATURAL RESISTANCE ASSOCIATED-MACROPHAGE PROTEIN3 (AtNRAMP3) and AtNRAMP4 function redundantly in Fe retrieval from vacuoles during germination.

Identification of mutations allowing Natural Resistance Associated Macrophage Proteins (NRAMP) to discriminate against cadmium.

Each essential transition metal plays a specific role in metabolic processes and has to be selectively transported. Living organisms need to discriminate between essential and non-essential metals such as cadmium (Cd(2+) ), which is highly toxic. However, transporters of the natural resistance-associated macrophage protein (NRAMP) family, which are involved in metal uptake and homeostasis, generally display poor selectivity towards divalent metal cations.

Mutants impaired in vacuolar metal mobilization identify chloroplasts as a target for cadmium hypersensitivity in Arabidopsis thaliana.

Cadmium (Cd) is highly toxic to plants causing growth reduction and chlorosis. It binds thiols and competes with essential transition metals. It affects major biochemical processes such as photosynthesis and the redox balance, but the connection between cadmium effects at the biochemical level and its deleterious effect on growth has seldom been established.

New ABA-hypersensitive Arabidopsis mutants are affected in loci mediating responses to water deficit and Dickeya dadantii infection.

On water deficit, abscisic acid (ABA) induces stomata closure to reduce water loss by transpiration. To identify Arabidopsis thaliana mutants which transpire less on drought, infrared thermal imaging of leaf temperature has been used to screen for suppressors of an ABA-deficient mutant (aba3-1) cold-leaf phenotype. Three novel mutants, called hot ABA-deficiency suppressor (has), have been identified with hot-leaf phenotypes in the absence of the aba3 mutation.

Constitutive activation of a plasma membrane H(+)-ATPase prevents abscisic acid-mediated stomatal closure.

Light activates proton (H(+))-ATPases in guard cells, to drive hyperpolarization of the plasma membrane to initiate stomatal opening, allowing diffusion of ambient CO(2) to photosynthetic tissues. Light to darkness transition, high CO(2) levels and the stress hormone abscisic acid (ABA) promote stomatal closing. The overall H(+)-ATPase activity is diminished by ABA treatments, but the significance of this phenomenon in relationship to stomatal closure is still debated.

Identification of features regulating OST1 kinase activity and OST1 function in guard cells.

The phytohormone abscisic acid (ABA) mediates drought responses in plants and, in particular, triggers stomatal closure. Snf1-related kinase 2 (SnRK2) proteins from several plant species have been implicated in ABA-signaling pathways. In Arabidopsis (Arabidopsis thaliana) guard cells, OPEN STOMATA 1 (OST1)/SRK2E/SnRK2-6 is a critical positive regulator of ABA signal transduction.

A network of local and redundant gene regulation governs Arabidopsis seed maturation.

In Arabidopsis thaliana, four major regulators (ABSCISIC ACID INSENSITIVE3 [ABI3], FUSCA3 [FUS3], LEAFY COTYLEDON1 [LEC1], and LEC2) control most aspects of seed maturation, such as accumulation of storage compounds, cotyledon identity, acquisition of desiccation tolerance, and dormancy. The molecular basis for complex genetic interactions among these regulators is poorly understood. By analyzing ABI3 and FUS3 expression in various single, double, and triple maturation mutants, we have identified multiple regulatory links among all four genes.

Characterization of three homologous basic leucine zipper transcription factors (bZIP) of the ABI5 family during Arabidopsis thaliana embryo maturation.

The Arabidopsis thaliana genome contains approximately 80 genes encoding basic leucine zipper transcription factors, divided into 11 groups. Abscisic Acid-Insensitive 5 (ABI5) is one of the 13 members of group A and is involved in ABA signalling during seed maturation, and germination. Seven other members of this group are expressed during seed maturation, but only one of them (Enhanced Em Level, EEL) has been functionally characterized during this developmental phase.

Analysis of an activated ABI5 allele using a new selection method for transgenic Arabidopsis seeds.

The Arabidopsis abscisic acid (ABA) insensitive (ABI)5 transcription factor participates in the ABA-dependent induction of late embryogenesis abundant (LEA) genes in the final stages of seed development. We tested whether the VP16 transcriptional activation domain is sufficient to provide ABI5 with the ability to activate the AtEm LEA genes in vegetative tissues. We took advantage of a new transgenic seed selection assay based on green fluorescent protein (GFP) fluorescence and found that VP16-ABI5 triggered growth retardation and ABA-independent induction of AtEm1 in seedlings.

ABSCISIC ACID SIGNAL TRANSDUCTION.

The plant hormone abscisic acid (ABA) plays a major role in seed maturation and germination, as well as in adaptation to abiotic environmental stresses. ABA promotes stomatal closure by rapidly altering ion fluxes in guard cells. Other ABA actions involve modifications of gene expression, and the analysis of ABA-responsive promoters has revealed a diversity of potential cis-acting regulatory elements.

Regulation of storage protein gene expression in Arabidopsis.

The expression of seed storage proteins is under tight developmental regulation and represents a powerful model system to study the regulation of gene expression during plant development. In this study, we show that three homologous B3 type transcription factors regulate the model storage protein gene, At2S3, via two distinct mechanisms: FUSCA3 (FUS3) and LEAFY COTYLEDON2 (LEC2) activate the At2S3 promoter in yeast suggesting that they regulate At2S3 by directly binding its promoter; ABSCISIC ACID INSENSITIVE3 (ABI3), however, appears to act more indirectly on At2S3, possibly as a cofactor in an activation complex. In accordance with this, FUS3 and LEC2 were found to act in a partially redundant manner and differently from ABI3 in planta: At2S3 expression is reduced to variable and sometimes only moderate extent in fus3 and lec2 single mutants but is completely abolished in the lec2 fus3 double mutant.

Arabidopsis OST1 protein kinase mediates the regulation of stomatal aperture by abscisic acid and acts upstream of reactive oxygen species production.

During drought, the plant hormone abscisic acid (ABA) triggers stomatal closure, thus reducing water loss. Using infrared thermography, we isolated two allelic Arabidopsis mutants (ost1-1 and ost1-2) impaired in the ability to limit their transpiration upon drought. These recessive ost1 mutations disrupted ABA induction of stomatal closure as well as ABA inhibition of light-induced stomatal opening.

The homologous ABI5 and EEL transcription factors function antagonistically to fine-tune gene expression during late embryogenesis.

In Arabidopsis, the basic leucine zipper transcription factor ABI5 activates several late embryogenesis-abundant genes, including AtEm1 and AtEm6. However, the expression of many other seed maturation genes is independent of ABI5. We investigated the possibility that ABI5 homologs also participate in the regulation of gene expression during seed maturation.

Use of infrared thermal imaging to isolate Arabidopsis mutants defective in stomatal regulation.

In response to drought, plants synthesise the hormone abscisic acid (ABA), which triggers closure of the stomatal pores. This process is vital for plants to conserve water by reducing transpirational water loss. Moreover, recent studies have demonstrated the advantages of the Arabidopsis stomatal guard cell for combining genetic, molecular and biophysical approaches to characterise ABA action.