Role of the Arabidopsis PIN6 Auxin Transporter in Auxin Homeostasis and Auxin-Mediated Development

Plant-specific PIN-formed (PIN) efflux transporters for the plant hormone auxin are required for tissue-specific directional auxin transport and cellular auxin homeostasis. The Arabidopsis PIN protein family has been shown to play important roles in developmental processes such as embryogenesis, organogenesis, vascular tissue differentiation, root meristem patterning and tropic growth. Here we analyzed roles of the less characterised Arabidopsis PIN6 auxin transporter. PIN6 is auxin-inducible and is expressed during multiple auxin–regulated developmental processes. Loss of pin6 function interfered with primary root growth and lateral root development. Misexpression of PIN6 affected auxin transport and interfered with auxin homeostasis in other growth processes such as shoot apical dominance, lateral root primordia development, adventitious root formation, root hair outgrowth and root waving. These changes in auxin-regulated growth correlated with a reduction in total auxin transport as well as with an altered activity of DR5-GUS auxin response reporter. Overall, the data indicate that PIN6 regulates auxin homeostasis during plant development.     

Anionic and zwitterionic moieties as widespread glycan modifications in non-vertebrates

Glycoconjugate Journal - Glycan structures in non-vertebrates are highly variable; it can be assumed that this is a product of evolution and speciation, not that it is just a random event. However,...     

A unifying conceptual model for the environmental responses of isoprene emissions from plants

Background and Aims

Isoprene is the most important volatile organic compound emitted by land plants in terms of abundance and environmental effects. Controls on isoprene emission rates include light, temperature, water supply and CO₂ concentration. A need to quantify these controls has long been recognized. There are already models that give realistic results, but they are complex, highly empirical and require separate responses to different drivers. This study sets out to find a simpler, unifying principle.

Methods

A simple model is presented based on the idea of balancing demands for reducing power (derived from photosynthetic electron transport) in primary metabolism versus the secondary pathway that leads to the synthesis of isoprene. This model''s ability to account for key features in a variety of experimental data sets is assessed.

Key results

The model simultaneously predicts the fundamental responses observed in short-term experiments, namely: (1) the decoupling between carbon assimilation and isoprene emission; (2) a continued increase in isoprene emission with photosynthetically active radiation (PAR) at high PAR, after carbon assimilation has saturated; (3) a maximum of isoprene emission at low internal CO₂ concentration (c_i) and an asymptotic decline thereafter with increasing c_i; (4) maintenance of high isoprene emissions when carbon assimilation is restricted by drought; and (5) a temperature optimum higher than that of photosynthesis, but lower than that of isoprene synthase activity.

Conclusions

A simple model was used to test the hypothesis that reducing power available to the synthesis pathway for isoprene varies according to the extent to which the needs of carbon assimilation are satisfied. Despite its simplicity the model explains much in terms of the observed response of isoprene to external drivers as well as the observed decoupling between carbon assimilation and isoprene emission. The concept has the potential to improve global-scale modelling of vegetation isoprene emission.     

Hemocytes and Plasma of the Eastern Oyster (Crassostrea virginica) Display a Diverse Repertoire of Sulfated and Blood Group A-modified N-Glycans

The eastern oyster (Crassostrea virginica) has become a useful model system for glycan-dependent host-parasite interactions due to the hijacking of the oyster galectin CvGal1 for host entry by the protozoan parasite Perkinsus marinus, the causative agent of Dermo disease. In this study, we examined the N-glycans of both the hemocytes, which via CvGal1 are the target of the parasite, and the plasma of the oyster. In combination with HPLC fractionation, exoglycosidase digestion, and fragmentation of the glycans, mass spectrometry revealed that the major N-glycans of plasma are simple hybrid structures, sometimes methylated and core α1,6-fucosylated, with terminal β1,3-linked galactose; a remarkable high degree of sulfation of such glycans was observed. Hemocytes express a larger range of glycans, including core-difucosylated paucimannosidic forms, whereas bi- and triantennary glycans were found in both sources, including structures carrying sulfated and methylated variants of the histo-blood group A epitope. The primary features of the oyster whole hemocyte N-glycome were also found in dominin, the major plasma glycoprotein, which had also been identified as a CvGal1 glycoprotein ligand associated with hemocytes. The occurrence of terminal blood group moieties on oyster dominin and on hemocyte surfaces can account in part for their affinity for the endogenous CvGal1.     

Fe(II) Oxidation Is an Innate Capability of Nitrate-Reducing Bacteria That Involves Abiotic and Biotic Reactions

Phylogenetically diverse species of bacteria can catalyze the oxidation of ferrous iron [Fe(II)] coupled to nitrate (NO₃⁻) reduction, often referred to as nitrate-dependent iron oxidation (NDFO). Very little is known about the biochemistry of NDFO, and though growth benefits have been observed, mineral encrustations and nitrite accumulation likely limit growth. Acidovorax ebreus, like other species in the Acidovorax genus, is proficient at catalyzing NDFO. Our results suggest that the induction of specific Fe(II) oxidoreductase proteins is not required for NDFO. No upregulated periplasmic or outer membrane redox-active proteins, like those involved in Fe(II) oxidation by acidophilic iron oxidizers or anaerobic photoferrotrophs, were observed in proteomic experiments. We demonstrate that while “abiotic” extracellular reactions between Fe(II) and biogenic NO₂⁻/NO can be involved in NDFO, intracellular reactions between Fe(II) and periplasmic components are essential to initiate extensive NDFO. We present evidence that an organic cosubstrate inhibits NDFO, likely by keeping periplasmic enzymes in their reduced state, stimulating metal efflux pumping, or both, and that growth during NDFO relies on the capacity of a nitrate-reducing bacterium to overcome the toxicity of Fe(II) and reactive nitrogen species. On the basis of our data and evidence in the literature, we postulate that all respiratory nitrate-reducing bacteria are innately capable of catalyzing NDFO. Our findings have implications for a mechanistic understanding of NDFO, the biogeochemical controls on anaerobic Fe(II) oxidation, and the production of NO₂⁻, NO, and N₂O in the environment.     

A Chemokine-Like Viral Protein Enhances Alpha Interferon Production by Plasmacytoid Dendritic Cells but Delays CD8+ T Cell Activation and Impairs Viral Clearance

Murine cytomegalovirus encodes numerous proteins that act on a variety of pathways to modulate the innate and adaptive immune responses. Here, we demonstrate that a chemokine-like protein encoded by murine cytomegalovirus activates the early innate immune response and delays adaptive immunity, thereby impairing viral clearance. The protein, m131/129 (also known as MCK-2), is not required to establish infection in the spleen; however, a mutant virus lacking m131/129 was cleared more rapidly from this organ. In the absence of m131/129 expression, there was enhanced activation of dendritic cells (DC), and virus-specific CD8⁺ T cells were recruited into the immune response earlier. Viral mutants lacking m131/129 elicited weaker production of alpha interferon (IFN-α) at 40 h postinfection, indicating that this protein exerts its effects during early rounds of viral replication in the spleen. Furthermore, while wild-type and mutant viruses activated plasmacytoid dendritic cells (pDC) equally at this time, as measured by the upregulation of costimulatory molecules, the presence of m131/129 stimulated more pDC to secrete IFN-α, accounting for the stronger IFN-α response than from the wild-type virus. These data provide evidence for a novel immunomodulatory function of a viral chemokine and expose the multifunctionality of immune evasion proteins. In addition, these results broaden our understanding of the interplay between innate and adaptive immunity.     

Levels of 5-methyltetrahydrofolate and ascorbic acid in cerebrospinal fluid are correlated: Implications for the accelerated degradation of folate by reactive oxygen species

Deficiency of 5-methyltetrahydrofolate (5-MTHF) in cerebrospinal fluid (CSF) is associated with a number of neurometabolic conditions including mitochondrial electron transport chain defects. Whilst failure of the active transport of 5-methyltetrahydrofolate (5-MTHF) into the CSF compartment has been proposed as a potential mechanism responsible for the 5-MTHF deficiency seen in mitochondrial disorders, it is becoming increasingly clear that other mechanisms are involved. Here, we have considered the role of oxidative stress as a contributing mechanism. Concerning, ascorbic acid (AA), we have established a CSF reference range (103–303 μM) and demonstrated a significant positive correlation between 5-MTHF and AA. Furthermore, CSF itself was also shown to convey antioxidant properties towards 5-MTHF. However, this protection could be overcome by the introduction of a hydroxyl radical generating system. Using a neuronal model system, inhibition of mitochondrial complex I, by 58%, was associated with a 23% increase in superoxide generation and a significantly increased loss of 5-MTHF from the extracellular medium. Addition of AA (150 μM) was able to prevent this increased 5-MTHF catabolism. We conclude that increased generation of reactive oxygen species and/or loss of CSF antioxidants are also factors to consider with regard to the development of a central 5-MTHF deficiency. Co-supplementation of AA together with appropriate folate replacement may be of therapeutic benefit.     

Proposal to replace the illegitimate genus name Prescottia Jones et al. 2013 with the genus name Prescottella gen. nov. and to replace the illegitimate combination Prescottia equi Jones et al. 2013 with Prescottella equi comb. nov

Recently we proposed that Rhodococcus equi (Magnusson 1923) Goodfellow and Alderson 1977 be transferred to a novel genus, Prescottia, as Prescottia equi comb. nov. However, in accordance with Principle 2 and Rule 51b(4) of the Bacteriological Code (1990 Revision), the bacterial genus name Prescottia Jones et al. 2013 is deemed illegitimate as this name has been used previously for a plant genus within the family Orchidaceae. Consequently, a new genus name, Prescottella gen. nov. is proposed for the bacterial taxon and a new combination Prescottella equi comb. nov. is proposed for the type species.     

Publication of descriptions of novel bacterial taxa in <Emphasis Type="Italic">Antonie van Leeuwenhoek</Emphasis>

The species from the order Neisseriales are currently distinguished from other bacteria on the basis of branching in 16S rRNA gene trees. For this order containing a single family, Neisseriaceae, no distinctive molecular, biochemical, or phenotypic characters are presently known. We report here detailed phylogenetic and comparative analyses on the 27 genome sequenced species of the order Neisseriales. Our comparative genomic analyses have identified 54 conserved signature indels (CSIs) in widely distributed proteins that are specific for either all of the sequenced Neisseriales species or a number of clades within this order that are also supported by phylogenetic analyses. Of these CSIs, 11 are specifically present in all of the sequenced species from this order, but are not found in homologous proteins from any other bacteria. These CSIs provide novel molecular markers specific for, and delimiting, this order. Twenty-one CSIs in diverse proteins are specific for a group comprised of the genera Neisseria, Eikenella, Kingella, and Simonsiella (Clade I), which are obligate host-associated organisms, lacking flagella and exhibiting varied morphology. The species from these genera also formed a strongly supported clade in phylogenetic trees based upon concatenated protein sequences; a monophyletic grouping of these genera and other genera displaying similar morphological characteristics was also observed in the 16S rRNA gene tree. A second clade (Clade II), supported by seven of the identified CSIs and phylogenetic trees based upon concatenated protein sequences, grouped together species from the genera Chromobacterium, Laribacter, and Pseudogulbenkiania that are rod-shaped bacteria, which display flagella-based motility and are capable of free living. The remainder of the CSIs were uniquely shared by smaller groups within these two main clades. Our analyses also provide novel insights into the evolutionary history of the Neisseriales and suggest that the CSIs that are specific for the Clade I species may play an important role in the evolution of obligate host-association within this order. On the basis of phylogenetic analysis, the identified CSIs, and conserved phenotypic characteristics of different Neisseriales genera, we propose a division of this order into two families: an emended family Neisseriaceae (corresponding to Clade I) containing the genera Alysiella, Bergeriella, Conchiformibius, Eikenella, Kingella, Neisseria, Simonsiella, Stenoxybacter, Uruburuella and Vitreoscilla and a new family, Chromobacteriaceae fam. nov., harboring the remainder of the genera from this order (viz. Andreprevotia, Aquaspirillum, Aquitalea, Chitinibacter, Chitinilyticum, Chitiniphilus, Chromobacterium, Deefgea, Formivibrio, Gulbenkiania, Iodobacter, Jeongeupia, Laribacter, Leeia, Microvirgula, Paludibacterium, Pseudogulbenkiania, Silvimonas, and Vogesella).