Bell-like homeodomain selectively regulates the high-irradiance response of phytochrome A.

Plant responses mediated by phytochrome A display a first phase saturated by transient light signals and a second phase requiring sustained excitation with far-red light (FR). These discrete outcomes, respectively so-called very-low-fluence response (VLFR) and high-irradiance response (HIR), are appropriate in different environmental and developmental contexts but the mechanisms that regulate the switch remain unexplored. Promoter analysis of a light-responsive target gene revealed a motif necessary for HIR but not for VLFR.

Abscisic acid, high-light, and oxidative stress down-regulate a photosynthetic gene via a promoter motif not involved in phytochrome-mediated transcriptional regulation.

In etiolated seedlings, light perceived by phytochrome promotes the expression of light-harvesting chlorophyll a/b protein of photosystem II (Lhcb) genes. However, excess of photosynthetically active radiation can reduce Lhcb expression. Here, we investigate the convergence and divergence of phytochrome, high-light stress and abscisic acid (ABA) signaling, which could connect these processes.

A constitutive shade-avoidance mutant implicates TIR-NBS-LRR proteins in Arabidopsis photomorphogenic development.

In plants, light signals caused by the presence of neighbors accelerate stem growth and flowering and induce a more erect position of the leaves, a developmental strategy known as shade-avoidance syndrome. In addition, mutations in the photoreceptors that mediate shade-avoidance responses enhance disease susceptibility in Arabidopsis thaliana. Here, we describe the Arabidopsis constitutive shade-avoidance1 (csa1) mutant, which shows a shade-avoidance phenotype in the absence of shade and enhanced growth of a bacterial pathogen.

Phytochrome control of the Arabidopsis transcriptome anticipates seedling exposure to light.

Phytochromes mediate a profound developmental shift when dark-grown seedlings are exposed to light. Here, we show that a subset of genes is upregulated in phytochrome B (phyB) mutants even before dark-grown Arabidopsis thaliana seedlings are exposed to light. Most of these genes bear the RY cis motif, which is a binding site of the transcription factor ABSCISIC ACID INSENSITIVE3 (ABI3), and the phyB mutation also enhances ABI3 expression.

Missense mutation in the PAS2 domain of phytochrome A impairs subnuclear localization and a subset of responses.

Phytochrome A signaling shows two photobiologically discrete outputs: so-called very-low-fluence responses (VLFR) and high-irradiance responses (HIR). By modifying previous screening protocols, we isolated two Arabidopsis mutants retaining VLFR and lacking HIR. Phytochrome A negatively or positively regulates phytochrome B signaling, depending on light conditions.

Hierarchical coupling of phytochromes and cryptochromes reconciles stability and light modulation of Arabidopsis development.

In plants, development is a continuing process that takes place under strong fluctuations of the light environment. Here we show that in Arabidopsis thaliana plants grown under intense white light, coupling of the photoreceptor cryptochrome 2 to developmental processes is broader than previously appreciated. Compared to the wild type, the cry2 mutant showed reduced activity of a Lhcb1*2 promoter fused to a reporter, and delayed flowering.

Sustained but not transient phytochrome A signaling targets a region of an Lhcb1*2 promoter not necessary for phytochrome B action.

Current evidence is inconclusive regarding the point of signaling convergence downstream from different members of the phytochrome family. In transgenic Arabidopsis, the activity of a reporter enzyme under the control of the -453 to +67 fragment of an Lhcb1*2 promoter shows very low fluence responses (VLFRs) and high-irradiance responses (HIRs) mediated by phytochrome A and low-fluence responses (LFRs) mediated by phytochrome B. A 5' deletion of the promoter to -134 abolished the HIR without affecting VLFR or LFR.

Regulation of phytochrome B signaling by phytochrome A and FHY1 in Arabidopsis thaliana.

Phytochrome A (phyA) and phytochrome B (phyB) share the control of many processes but little is known about mutual signaling regulation. Here, we report on the interactions between phyA and phyB in the control of the activity of an Lhcb1*2 gene fused to a reporter, hypocotyl growth and cotyledon unfolding in etiolated Arabidopsis thaliana. The very-low fluence responses (VLFR) induced by pulsed far-red light and the high-irradiance responses (HIR) observed under continuous far-red light were absent in the phyA and phyA phyB mutants, normal in the phyB mutant, and reduced in the fhy1 mutant that is defective in phyA signaling.

Different phototransduction kinetics of phytochrome A and phytochrome B in Arabidopsis thaliana.

The kinetics of phototransduction of phytochrome A (phyA) and phytochrome B (phyB) were compared in etiolated Arabidopsis thaliana seedlings. The responses of hypocotyl growth, cotyledon unfolding, and expression of a light-harvesting chlorophyll a/b-binding protein of the photosystem II gene promoter fused to the coding region of beta-glucuronidase (used as a reporter enzyme) were mediated by phyA under continuous far-red light (FR) and by phyB under continuous red light (R). The seedlings were exposed hourly either to n min of FR followed by 60 minus n min in darkness or to n min of R, 3 min of FR (to back-convert phyB to its inactive form), and 57 minus n min of darkness.

A 146 bp fragment of the tobacco Lhcb1*2 promoter confers very-low-fluence, low-fluence and high-irradiance responses of phytochrome to a minimal CaMV 35S promoter.

The occurrence of very-low-fluence responses (VLFR), low-fluence responses (LFR) and high-irradiance responses (HIR) of phytochrome was investigated for the expression of the gene of beta-glucuronidase (gusA) under the control of the tobacco Lhcb1*2 promoter, in etiolated transgenic tobacco seedlings. The activity of beta-glucuronidase (GUS) showed biphasic responses to the calculated proportion of Pfr provided by light pulses. The first phase (i.

Characterization and regulation of the expression of the Solanum tuberosum Lhcb1 genes.

A potato (Solanum tuberosum) genomic library was used to isolate five full-length genes and part of a sixth one, encoding the apoproteins of a light-harvesting complex (LHC). The nucleotide sequences of the five isolated genes showed that they encoded very similar proteins (99.75% to 97.

Characterization of a high-affinity iron transport system in Acinetobacter baumannii.

Analysis of a clinical isolate of Acinetobacter baumannii showed that this bacterium was able to grow under iron-limiting conditions, using chemically defined growth media containing different iron chelators such as human transferrin, ethylenediaminedi-(o-hydroxyphenyl)acetic acid, nitrilotriacetic acid, and 2,2'-bipyridyl. This iron uptake-proficient phenotype was due to the synthesis and secretion of a catechol-type siderophore compound. Utilization bioassays using the Salmonella typhimurium iron uptake mutants enb-1 and enb-7 proved that this siderophore is different from enterobactin.

Molecular characterization of two clusters of genes encoding the Type I CAB polypeptides of PSII in Nicotiana plumbaginifolia.

A Nicotiana plumbaginifolia genomic library in the phage Charon 34 was used to isolate and characterize 7 full-length genes and part of an 8th gene encoding chlorophyll a/b-binding (CAB) polypeptides. These genes are arranged in two clusters. All the genes within the clusters are arranged in opposite orientation to their neighbours.

The enzymatic synthesis of beta 1-2 glucans.

Incubation of labeled uridine diphosphate glucose with an enzyme preparation from Rhizobium meliloti or Agrobacterium tumefaciens leads to the formation of a glucan which appears to be identical to the beta 1-2 cyclic glucan described by several workers. This conclusion is based on the molecular size, the formation of sophorose and higher homologs by partial acid hydrolysis, the liberation of only glucose by total acid hydrolysis, and the release of only 3,4,6-tri-O-methylglucose after methylation and hydrolysis. A snail intestinal juice enzyme was found to break down the glucan and its partial hydrolysis products.

Identification and genetic analysis of an Agrobacterium tumefaciens chromosomal virulence region.

A genetic analysis of Agrobacterium tumefaciens chromosomal functions required for virulence was undertaken. Large Tn5-containing cosmid clones were isolated from DNA of avirulent A. tumefaciens mutants having chromosomal Tn5 insertions and exhibiting defective attachment to plant cells.

Lipid-bound saccharides in Rhizobium meliloti.

The lipid-bound saccharides formed by incubation of uridine diphosphate glucose with a particulate enzyme of Rhizobium meliloti were studied. They behaved like polyprenyl diphosphate saccharides when treated with ammonia or hot phenol, when catalytically hydrogenated, and on DEAE-cellulose chromatography. The saccharide moieties obtained after heating at pH 2 for 10 min at 100 degrees C were separated with a gel filtration column.

The biosynthetic pathway of the asparagine-linked oligosaccharides of glycoproteins.

This review deals with the structure and addition of the different types of oligosaccharides to asparagine residues in proteins. This process occurs in several steps, first an oligosaccharide which contains N-acetylglucosamine mannose and glucose is built up joined to dolichyl diphosphate. The oligosaccharide is then transferred to a polypeptide chain, loses its glucose, and is modified by removal of some monosaccharides and addition of others giving rise to a variety of saccharides.

Transfer of oligosaccharide to protein from a lipid intermediate in plants.

A lipid-bound oligosaccharide was isolated from pea (Pisum sativum) cotyledons incubated with [(14)C]mannose. The oligosaccharide moiety appeared to be identical with the one obtained from rat liver, known to contain three glucoses, nine mannoses, and two N-acetylglucosamines, and to be involved in protein glycosylation.Enzymes obtained from soya (Glycine max) roots and developing pea cotyledons were found to catalyze the transfer of oligosaccharide from the lipid intermediate to endogenous protein.

Microsomal glucosidases of rat liver. Partial purification and inhibition by disaccharides.

Further work on microsomal glucosidases of rat liver has confirmed that at least two enzymes are involved in the removal of glucose from the glucose-containing oligosaccharide. One acts on the oligosaccharide containing three glucose residues and another on the oligosaccharide which has one or two glucoses. The glucosidase which acts on (Glc)2(Man)9(GlcNAc)2 could be purified with a Concanavalin-A--Sepharose column following by electrofocusing.

Presence in a plant of a compound similar to the dolichyl diphosphate oligosaccharide of animal tissue.

A compound with properties identical with the glucose-containing dolichyl diphosphate oligosaccharide present in animal tissues was detected in alfalfa roots incubated with [14C]glucose. The products of mild acid hydrolysis behaved the same on paper chromatography, on treatment with specific glucosidases and on N-deacetylation.

Addition of glucose to dolichyl diphosphate oligosaccharide and transfer to protein.

The glycosylation of asparagine residues in proteins is known to occur by transfer from a dolichyl diphosphate oligosaccharide containing glucose. Paper chromatography allowed the separation of oligosaccharides (obtained by acid hydrolysis of the dolichyl diphosphate derivative) containing 1, 2 and 3 glucose residues. Using this procedure it was found that the addition of all three glucoses to the dolichyl diphosphate oligosaccharide occur with dolichyl phosphate glucose as donor.