Rhizobacterial volatiles affect the growth of fungi and Arabidopsis thaliana

Volatiles of Stenotrophomonas, Serratia, and Bacillus species inhibited mycelial growth of many fungi and Arabidopsis thaliana (40 to 98%), and volatiles of Pseudomonas species and Burkholderia cepacia retarded the growth to lesser extents. Aspergillus niger and Fusarium species were resistant, and B. cepacia and Staphylococcus epidermidis promoted the growth of Rhizoctonia solani and A. thaliana. Bacterial volatiles provide a new source of compounds with antibiotic and growth-promoting features.     

Volatiles of bacterial antagonists inhibit mycelial growth of the plant pathogen <Emphasis Type="Italic">Rhizoctonia solani</Emphasis>

Bacterial antagonists are bacteria that negatively affect the growth of other organisms. Many antagonists inhibit the growth of fungi by various mechanisms, e.g., secretion of lytic enzymes, siderophores and antibiotics. Such inhibition of fungal growth may indirectly support plant growth. Here, we demonstrate that small organic volatile compounds (VOCs) emitted from bacterial antagonists negatively influence the mycelial growth of the soil-borne phytopathogenic fungus Rhizoctonia solani Kühn. Strong inhibitions (99–80%) under the test conditions were observed with Stenotrophomonas maltophilia R3089, Serratia plymuthica HRO-C48, Stenotrophomonas rhizophila P69, Serratia odorifera 4Rx13, Pseudomonas trivialis 3Re2-7, S. plymuthica 3Re4-18 and Bacillus subtilis B2g. Pseudomonas fluorescens L13-6-12 and Burkholderia cepacia 1S18 achieved 30% growth reduction. The VOC profiles of these antagonists, obtained through headspace collection and analysis on GC-MS, show different compositions and complexities ranging from 1 to almost 30 compounds. Most volatiles are species-specific, but overlapping volatile patterns were found for Serratia spp. and Pseudomonas spp. Many of the bacterial VOCs could not be identified for lack of match with mass-spectra of volatiles in the databases.     

The TTX metabolite 4,9-anhydro-TTX is a highly specific blocker of the Na(v1.6) voltage-dependent sodium channel

The blocking efficacy of 4,9-anhydro-TTX (4,9-ah-TTX) and TTX on several isoforms of voltage-dependent sodium channels, expressed in Xenopus laevis oocytes, was tested (Na_v1.2, Na_v1.3, Na_v1.4, Na_v1.5, Na_v1.6, Na_v1.7, and Na_v1.8). Generally, TTX was 40–231 times more effective, when compared with 4,9-ah-TTX, on a given isoform. An exception was Na_v1.6, where 4,9-ah-TTX in nanomole per liter concentrations sufficed to result in substantial block, indicating that 4,9-ah-TTX acts specifically at this peculiar isoform. The IC₅₀ values for TTX/4,9-ah-TTX were as follows (in nmol/l): 7.8 ± 1.3/1,260 ± 121 (Na_v1.2), 2.8 ± 2.3/341 ± 36 (Na_v1.3), 4.5 ± 1.0/988 ± 62 (Na_v1.4), 1,970 ± 565/78,500 ± 11,600 (Na_v1.5), 3.8 ± 1.5/7.8 ± 2.3 (Na_v1.6), 5.5 ± 1.4/1,270 ± 251 (Na_v1.7), and 1,330 ± 459/>30,000 (Na_v1.8). Analysis of approximal half-maximal doses of both compounds revealed minor effects on voltage-dependent activation only, whereas steady-state inactivation was shifted to more negative potentials by both TTX and 4,9-ah-TTX in the case of the Na_v1.6 subunit, but not in the case of other TTX-sensitive ones. TTX shifted steady-state inactivation also to more negative potentials in case of the TTX-insensitive Na_v1.5 subunit, where it also exerted profound effects on the time course of recovery from inactivation. Isoform-specific interaction of toxins with ion channels is frequently observed in the case of proteinaceous toxins. Although the sensitivity of Na_v1.1 to 4,9-ah-TTX is not known, here we report evidence on a highly isoform-specific TTX analog that may well turn out to be an invaluable tool in research for the identification of Na_v1.6-mediated function, but also for therapeutic intervention. sodium channel; tetrodotoxin     

Localization of the iron-regulatory proteins hemojuvelin and transferrin receptor 2 to the basolateral membrane domain of hepatocytes

The newly discovered proteins hemojuvelin (Hjv) and transferrin receptor type 2 (TfR2) are involved in iron metabolism. Mutations in the Hjv and TfR2 gene cause hemochromatosis. We investigated the expression and cellular localization of Hjv and TfR2 in rat and human liver. The expression of Hjv and TfR2 was shown on mRNA and protein level by RT–PCR and immunoblot experiments. Their cellular localization was studied by immunofluorescence with antibodies raised against Hjv and TfR2. Hjv and TfR2 are present in human and rat liver and in primary human hepatocytes. Antisera raised against Hjv identified immunoreactive proteins with an apparent size of 44 and 46 kDa in immunoblot experiments of rat and human liver extracts, which are in accordance with the putative membrane-bound and cleaved soluble forms of this protein, respectively. TfR2 was detected as a 105 kDa protein corresponding to the predicted size of glycosylated TfR2 monomers. In immunofluorescence experiments, Hjv and TfR2 were found in rat liver only in hepatocytes. At the subcellular level, both proteins were predominantly localized to the basolateral membrane domain of hepatocytes. The localization of Hjv and TfR2 at the same membrane domain renders a functional interaction of these two proteins in iron homeostasis possible. Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at . Kulaksiz and Stremmel contributed equally to this work.     

The Wilms tumor genes wt1a and wt1b control different steps during formation of the zebrafish pronephros

The Wilms tumor protein WT1 is an essential factor for kidney development. In humans, mutations in WT1 lead to Wilms tumor, a pediatric kidney cancer as well as to developmental anomalies concerning the urogenital tract. Inactivation of Wt1 in mice causes multiple organ defects most notably agenesis of the kidneys. In zebrafish, two paralogous wt1 genes exist, wt1a and wt1b. The wt1 genes are expressed in a similar and overlapping but not identical pattern. Here, we have examined the role of both wt1 genes in early kidney development employing a transgenic line with pronephros specific GFP expression and morpholino knockdown experiments. Inactivation of wt1a led to failure of glomerular differentiation and morphogenesis resulting in a rapidly expanding general body edema. In contrast, knockdown of wt1b was compatible with early glomerular development. After 48 h, however, wt1b morphant embryos developed cysts in the region of the glomeruli and tubules and subsequent pericardial edema at 4 days post-fertilization. Thus, our data suggest different functions for wt1a and wt1b in zebrafish nephrogenesis. While wt1a has a more fundamental and early role in pronephros development and is essential for the formation of glomerular structures, wt1b functions at later stages of nephrogenesis.     

An improved molecular phylogeny of the Nematoda with special emphasis on marine taxa

Phylogenetic reconstructions of relations within the phylum Nematoda are inherently difficult but have been advanced with the introduction of large-scale molecular-based techniques. However, the most recent revisions were heavily biased towards terrestrial and parasitic species and greater representation of clades containing marine species (e.g. Araeolaimida, Chromadorida, Desmodorida, Desmoscolecida, Enoplida, and Monhysterida) is needed for accurate coverage of known taxonomic diversity. We now add small subunit ribosomal DNA (SSU rDNA) sequences for 100 previously un-sequenced species of nematodes, including 46 marine taxa. SSU rDNA sequences for >200 taxa have been analysed based on Bayesian inference and LogDet-transformed distances. The resulting phylogenies provide support for (i) the re-classification of the Secernentea as the order Rhabditida that derived from a common ancestor of chromadorean orders Araeolaimida, Chromadorida, Desmodorida, Desmoscolecida, and Monhysterida and (ii) the position of Bunonema close to the Diplogasteroidea in the Rhabditina. Other, previously controversial relationships can now be resolved more clearly: (a) Alaimus, Campydora, and Trischistoma belong in the Enoplida, (b) Isolaimium is placed basally to a big clade containing the Axonolaimidae, Plectidae, and Rhabditida, (c) Xyzzors belongs in the Desmodoridae, (d) Comesomatidae and Cyartonema belongs in the Monhysterida, (e) Globodera belongs in the Hoplolaimidae and (f) Paratylenchus dianeae belongs in the Criconematoidea. However, the SSU gene did not provide significant support for the class Chromadoria or clear evidence for the relationship between the three classes, Enoplia, Dorylaimia, and Chromadoria. Furthermore, across the whole phylum, the phylogenetically informative characters of the SSU gene are not informative in a parsimony analysis, highlighting the short-comings of the parsimony method for large-scale phylogenetic modelling.     

Incongruent plastid and nuclear DNA phylogenies reveal ancient intergeneric hybridization in Pilosella hawkweeds (Hieracium, Cichorieae, Asteraceae)

Phylogenetic relationships for Hieracium subgen. Pilosella were inferred from chloroplast (trnT-trnL, matK) and nuclear (ITS) sequence data. Chloroplast markers revealed the existence of two divergent haplotype groups within the subgenus that did not correspond to presumed relationships. Furthermore, chloroplast haplotypes of the genera Hispidella and Andryala nested each within one of these groups. In contrast, ITS data were generally in accord with morphology and other evidence and were therefore assumed to reflect the true phylogeny. They revealed a sister relationship between Pilosella and Hispidella and a joint clade of Hieracium subgenera Hieracium and Chionoracium (Stenotheca) while genus Andryala represented a third major lineage of the final ingroup cluster. Detailed analysis of trnT-trnL character state evolution along the ITS tree suggested two intergeneric hybridization events between ancestral lineages that resulted in cytoplasmic transfer (from Hieracium/Chionoracium to Pilosella, and from the introgressed Pilosella lineage to Andryala). These chloroplast capture events, the first of which involved a now extinct haplotype, are the most likely explanation for the observed incongruencies between plastid and nuclear DNA markers.     

A novel, single nucleotide polymorphism-based assay to detect 22q11 deletions

Velocardiofacial syndrome, DiGeorge syndrome, and conotruncal anomaly face syndrome, now collectively referred to as 22q11deletion syndrome (22q11DS) are caused by microdeletions on chromosome 22q11. The great majority ( approximately 90%) of these deletions are 3 Mb in size. The remaining deleted patients have nested break-points resulting in overlapping regions of hemizygosity. Diagnostic testing for the disorder is traditionally done by fluorescent in situ hybridization (FISH) using probes located in the proximal half of the region common to all deletions. We developed a novel, high-resolution single-nucleotide polymorphism (SNP) genotyping assay to detect 22q11 deletions. We validated this assay using DNA from 110 nondeleted controls and 77 patients with 22q11DS that had previously been tested by FISH. The assay was 100% sensitive (all deletions were correctly identified). Our assay was also able to detect a case of segmental uniparental disomy at 22q11 that was not detected by the FISH assay. We used Bayesian networks to identify a set of 17 SNPs that are sufficient to ascertain unambiguously the deletion status of 22q11DS patients. Our SNP based assay is a highly accurate, sensitive, and specific method for the diagnosis of 22q11 deletion syndrome.