Bacterial present in the xylem of coffee (Rubiaceae: coffea arabica) with "Crespera" disease

"Crespera" is an infectious disease of coffee plants that affects both the coffee production and the economy of the coffee producer countries. This disease affects morphologically the plant: long and narrow leaves with wavy borders and marginal necrosis; strong chlorosis results in drying of the leave, and leads to bad conditions of the plant. The internodes are short, producing the appearance of multiple sprouts in the axial sprout, the flowers can turn greenish, and the plant can present branches with severe symptoms, and branches without apparent symptoms at the same time. As a result, the coffee bean production decreases strikingly. The aim of this work was to determine the occurrence of the possible causative agent in the coffee plants using transmission electron microscopy. Normal and infected plants were compared looking at the leaves, central vein, lateral veins and petiole. It was determined that xylematic vessels show the presence of gram negative bacilliform bacteria (of thick-wavy walls), with dimensions of 0.3-0.5 micron diameter and 1-4 microns, length. The control plants did not show bacteria in the xylem.     

Cold sweetening in diploid potato: mapping quantitative trait loci and candidate genes

A candidate gene approach has been used as a first step to identify the molecular basis of quantitative trait variation in potato. Sugar content of tubers upon cold storage was the model trait chosen because the metabolic pathways involved in starch and sugar metabolism are well known and many of the genes have been cloned. Tubers of two F(1) populations of diploid potato grown in six environments were evaluated for sugar content after cold storage. The populations were genotyped with RFLP, AFLP, and candidate gene markers. QTL analysis revealed that QTL for glucose, fructose, and sucrose content were located on all potato chromosomes. Most QTL for glucose content mapped to the same positions as QTL for fructose content. QTL explaining >10% of the variability for reducing sugars were located on linkage groups I, III, VII, VIII, IX, and XI. QTL consistent across populations and/or environments were identified. QTL were linked to genes encoding invertase, sucrose synthase 3, sucrose phosphate synthase, ADP-glucose pyrophosphorylase, sucrose transporter 1, and a putative sucrose sensor. The results suggest that allelic variants of enzymes operating in carbohydrate metabolic pathways contribute to the genetic variation in cold sweetening.     

Ligation of HLA class I molecules on endothelial cells induces phosphorylation of Src,paxillin, and focal adhesion kinase in an actin-dependent manner

The development of chronic rejection is the major limitation to long-term allograft survival. HLA class I Ags have been implicated to play a role in this process because ligation of class I molecules by anti-HLA Abs stimulates smooth muscle cell and endothelial cell proliferation. In this study, we show that ligation of HLA class I molecules on the surface of human aortic endothelial cells stimulates phosphorylation of Src, focal adhesion kinase, and paxillin. Signaling through class I stimulated Src phosphorylation and mediated fibroblast growth factor receptor (FGFR) translocation to the nucleus. In contrast, Src kinase activity was not involved in class I-mediated transfer of FGFR from cytoplasmic stores to the cell surface. Inhibition of Src protein kinase activity blocked HLA class I-stimulated tyrosine phosphorylation of paxillin and focal adhesion kinase. Furthermore, HLA class I-mediated phosphorylation of the focal adhesion proteins and FGFR expression was inhibited by cytochalasin D and latrunculin A, suggesting a role for the actin cytoskeleton in the signaling process. These findings indicate that anti-HLA Abs have the capacity to transduce activation signals in endothelial cells that may promote the development of chronic rejection.     

Effects of copper on algal communities at different current velocities

This study examines the influence of current velocity in the toxiceffect of copper in diatom-dominated biofilms grown in artificial channels.Effects on community structure, algal biomass and photosynthesis (carbonincorporation) caused by 15 g L^–1 of copperwere tested at contrasting (1 and 15 cm s^–1)velocities. Moreover, a possible threshold on the effect of copper on algalbiomass and photosynthesis related to current velocity was examined by usingprogressively increasing current velocity (1 to 50 cms^–1) at 15 g L^–1 Cu.Chlorophyll-a decreased ca. 50% as a result of addition of15 g L^–1 Cu. Chlorophyll decrease occurredearlier at 15 cm s^–1 than at 1 cms^–1 when adding 15 g L^–1Cu. Copper also caused a remarkable decrease in carbon incorporation(from 30 to ca. 50%), which was produced earlier at 15 cms^–1 (three days) than at 1 cms^–1 (seven days). Some taxa were affected by thecombination of copper and current velocity. Both Achnanthesminutissima and Stigeoclonium tenue becomedominant at 15 cm s^–1 in the presence of copper.Significant inhibition of algal growth in 15 g L^–1Cu occurred at low (1 cm s^–1) and highvelocities (50 cm s^–1), but not at intermediatevelocity (20 cm s^–1). The experiments indicatethat current velocity triggers the effect that copper has on diatom-dominatedbiofilms, and that the effect is more remarkable at low and high than atintermediate current velocities.     

TranScout: prediction of gene expression regulatory proteins from their sequences

MOTIVATION: The advent of genomics yields thousands of reading frames in search of function. Identification of conserved functional motifs in protein sequences can be helpful for function prediction. RESULTS: A database and a classification of reported DNA-binding protein motifs has been designed. A program ('TranScout') has been developed for the detection and evaluation of conserved motifs in prokaryotic and eukaryotic sequences of proteins with a gene regulatory function. The efficiency of the program is shown in a benchmark against a database obtained from SWISS-PROT without the protein sequences used to train the program. All motifs were detected with a mean average sensitivity of 0.98 and a mean average specificity of 0.92. AVAILABILITY: The program is freely available for use on the internet at http://luz.uab.es/transcout/. The user can find additional information at this site.     

Nitric oxide and cell signaling pathways in mitochondrial-dependent apoptosis

Nitric oxide, generated by endogenous nitric oxide synthases or nitric oxide donors, can promote or prevent apoptosis induced by diverse pro-apoptotic stimuli in cell culture models. Both mitochondrial-dependent and -independent apoptotic signaling pathways mediate this dichotomous cellular response to nitric oxide. The molecular mechanisms behind these effects are complex and involve a number of nitrogen oxide-related species that are more reactive than nitric oxide itself. The local cellular environment plays a dynamic role in determining the nature and concentration of these species. Important components of the microenvironment include: the cellular redox state, glutathione, transition metals and the presence of other oxygen- and nitrogen-centered radicals. In particular, redox-sensitive nitrosating species are favorably generated under physiological conditions and capable of modifying multiple cell signaling pathways through reversible S-nitrosation reactions. Cytochrome c release from mitochondria is an important mechanism for the activation of caspase-3 and the initiation of cell death in response to 'intrinsic' pro-apoptotic stimuli, including oxidative and nitrosative stress. In turn, caspases and mitogen associated protein kinases may modulate cytochrome c release through their effects on the Bcl-2 family of proteins. This review will focus on (i) the importance of the cellular environment in determining the fate of nitric oxide and (ii) the ability of S-nitrosation to regulate mitochondrial-dependent apoptosis at the level of mitochondrial bioenergetics, cytochrome c release, caspases, mitogen associated protein kinases, and the Bcl-2 family of proteins.     

Purification,cofactor analysis,and site-directed mutagenesis of Synechococcus ferredoxin-nitrate reductase

The narB gene of the cyanobacterium Synechococcus sp. strain PCC 7942 encodes an assimilatory nitrate reductase that uses photosynthetically reduced ferredoxin as the physiological electron donor. This gene was expressed in Escherichia coli and electrophoretically pure preparations of the enzyme were obtained using affinity chromatography with either reduced-ferredoxin or NarB antibodies. The electronic absorption spectrum of the oxidized enzyme showed a shoulder at around 320 nm and a broad absorption band between 350 and 500 nm. These features are indicative of the presence of an iron-sulfur centre(s) and accordingly metal analysis showed ca. 3 atoms of Fe per molecule of protein that could represent a [3Fe-4S] cluster. Further analysis indicated the presence of 1 atom of Mo and 2 molecules of ribonucleotide-conjugated molybdopterin per molecule of protein. This, together with the requirement of a mobA gene for production of an active enzyme, strongly suggests the presence of Mo in the form of the bis-MGD (bis-molybdopterin guanine dinucleotide) cofactor in Synechococcusnitrate reductase. A model for the coordination of the Mo atom to the enzyme is proposed. Four conserved Cys residues were replaced by site-directed mutagenesis. The effects of these changes on the enzyme activity and electronic absorption spectra support the participation of those residues in iron-sulfur cluster coordination. This revised version was published online in June 2006 with corrections to the Cover Date.