Auxin acts independently of DELLA proteins in regulating gibberellin levels

Shoot elongation is a vital process for plant development and productivity, in both ecological and economic contexts. Auxin and bioactive gibberellins (GAs), such as GA₁, play critical roles in the control of elongation,^1–3 along with environmental and endogenous factors, including other hormones such as the brassinosteroids.^4,5 The effect of auxins, such as indole-3-acetic acid (IAA), is at least in part mediated by its effect on GA metabolism,⁶ since auxin upregulates biosynthesis genes such as GA 3-oxidase and GA 20-oxidase and downregulates GA catabolism genes such as GA 2-oxidases, leading to elevated levels of bioactive GA₁.⁷ In our recent paper,¹ we have provided evidence that this action of IAA is largely independent of DELLA proteins, the negative regulators of GA action,^8,9 since the auxin effects are still present in the DELLA-deficient la cry-s genotype of pea. This was a crucial issue to resolve, since like auxin, the DELLAs also promote GA₁ synthesis and inhibit its deactivation. DELLAs are deactivated by GA, and thereby mediate a feedback system by which bioactive GA regulates its own level.¹⁰ However, our recent results,¹ in themselves, do not show the generality of the auxin-GA relationship across species and phylogenetic groups or across different tissue types and responses. Further, they do not touch on the ecological benefits of the auxin-GA interaction. These issues are discussed below as well as the need for the development of suitable experimental systems to allow this process to be examined.Key words: auxin, gibberellins, DELLA proteins, interactions, elongation     

Ku must load directly onto the chromosome end in order to mediate its telomeric functions

The Ku heterodimer associates with the Saccharomyces cerevisiae telomere, where it impacts several aspects of telomere structure and function. Although Ku avidly binds DNA ends via a preformed channel, its ability to associate with telomeres via this mechanism could be challenged by factors known to bind directly to the chromosome terminus. This has led to uncertainty as to whether Ku itself binds directly to telomeric ends and whether end association is crucial for Ku's telomeric functions. To address these questions, we constructed DNA end binding-defective Ku heterodimers by altering amino acid residues in Ku70 and Ku80 that were predicted to contact DNA. These mutants continued to associate with their known telomere-related partners, such as Sir4, a factor required for telomeric silencing, and TLC1, the RNA component of telomerase. Despite these interactions, we found that the Ku mutants had markedly reduced association with telomeric chromatin and null-like deficiencies for telomere end protection, length regulation, and silencing functions. In contrast to Ku null strains, the DNA end binding defective Ku mutants resulted in increased, rather than markedly decreased, imprecise end-joining proficiency at an induced double-strand break. This result further supports that it was the specific loss of Ku's telomere end binding that resulted in telomeric defects rather than global loss of Ku's functions. The extensive telomere defects observed in these mutants lead us to propose that Ku is an integral component of the terminal telomeric cap, where it promotes a specific architecture that is central to telomere function and maintenance.     

Identification, replication, and fine-mapping of Loci associated with adult height in individuals of african ancestry

Adult height is a classic polygenic trait of high heritability (h ² ∼0.8). More than 180 single nucleotide polymorphisms (SNPs), identified mostly in populations of European descent, are associated with height. These variants convey modest effects and explain ∼10% of the variance in height. Discovery efforts in other populations, while limited, have revealed loci for height not previously implicated in individuals of European ancestry. Here, we performed a meta-analysis of genome-wide association (GWA) results for adult height in 20,427 individuals of African ancestry with replication in up to 16,436 African Americans. We found two novel height loci (Xp22-rs12393627, P = 3.4×10⁻¹² and 2p14-rs4315565, P = 1.2×10⁻⁸). As a group, height associations discovered in European-ancestry samples replicate in individuals of African ancestry (P = 1.7×10⁻⁴ for overall replication). Fine-mapping of the European height loci in African-ancestry individuals showed an enrichment of SNPs that are associated with expression of nearby genes when compared to the index European height SNPs (P<0.01). Our results highlight the utility of genetic studies in non-European populations to understand the etiology of complex human diseases and traits.     

Pervasive sign epistasis between conjugative plasmids and drug-resistance chromosomal mutations

Multidrug-resistant bacteria arise mostly by the accumulation of plasmids and chromosomal mutations. Typically, these resistant determinants are costly to the bacterial cell. Yet, recently, it has been found that, in Escherichia coli bacterial cells, a mutation conferring resistance to an antibiotic can be advantageous to the bacterial cell if another antibiotic-resistance mutation is already present, a phenomenon called sign epistasis. Here we study the interaction between antibiotic-resistance chromosomal mutations and conjugative (i.e., self-transmissible) plasmids and find many cases of sign epistasis (40%)--including one of reciprocal sign epistasis where the strain carrying both resistance determinants is fitter than the two strains carrying only one of the determinants. This implies that the acquisition of an additional resistance plasmid or of a resistance mutation often increases the fitness of a bacterial strain already resistant to antibiotics. We further show that there is an overall antagonistic interaction between mutations and plasmids (52%). These results further complicate expectations of resistance reversal by interdiction of antibiotic use.     

C terminus of the P2X7 receptor: treasure hunting

P2X receptor (P2XR) is a family of the ATP-gated ion channel family and can permeabilize the plasma membrane to small cations such as potassium, sodium, and calcium, resulting in cellular depolarization. There are seven P2XR that have been described and cloned, with 45% identity in amino acid sequence. Each P2X receptors has two transmembrane domains that are separated by an extracellular loop and an intracellular N and C terminus. Unlike the other P2X receptors, the P2X7R has a larger C terminus with an extra 200 amino acid residues compared with the other receptors. The C terminus of the P2X7R has been implicated in regulating receptor function including signaling pathway activation, cellular localization, protein–protein interactions, and post-translational modification (PTM). In the present review, we discuss the role of the P2X7R C terminus in regards to receptor function, describe the specific domains and motifs found therein and compare the C terminus sequence with others proteins to discover predicted domains or sites of PTM.     

Phenolic derivatives from Ruprechtia polystachya and their inhibitory activities on the glucose-6-phosphatase system

Two new compounds, 5-methyl-2-(2-methylbutanoyl)phloroglucinol 1-O-(6-O-β-D-apiofuranosyl)-β-D-glucopyranoside (1) and trans-2,3-dihydrokaempferol 3-O-(4-O-sulfo)-α-L-arabinopyranoside (2), together with 14 known flavonoids, trans-dihydrokaempferol 3-O-α-L-arabinopyranoside (3), trans-taxifolin 3-O-α-L-arabinofuranoside (4), quercetin 3-O-α-L-rhamnopyranoside (5), quercetin 3'-O-α-L-arabinofuranoside (6), catechin 3-O-α-L-rhamnopyranoside (7), trans-taxifolin 3-O-α-L-arabinopyranoside (8), cis-dihydrokaempferol 3-O-α-L-arabinopyranoside (9), catechin (10), myricetin 3-O-α-L-rhamnopyranoside (11), quercetin 3-O-α-L-arabinopyranoside (12), quercetin 3-O-α-L-arabinofuranoside (13), quercetin 3-O-(3″-galloyl)-α-L-rhamnopyranoside (14), quercetin 3-O-(2″-galloyl)-α-L-rhamnopyranoside (15), and epicatechin 3-O-gallate (16), were isolated from the leaves of Ruprechtia polystachya Griseb. (Polygonaceae). Their structures were established on the basis of extensive 1D- and 2D-NMR experiments as well as MS analyses. All compounds, except 1, showed inhibition of the enzyme glucose-6-phosphatase in intact microsomes.     

Resolving the phylogenetic relationships and evolutionary history of the Drosophila virilis group using multilocus data

The Drosophila virilis group is one of the major lineages of Drosophila previously recognised and it has been used as a model for different types of studies. It comprises 13 species whose phylogenetic relationships are not well resolved. In the present study, six nuclear genes (Adh, fused, Gpdh, NonA, CG9631 and CG7219) and the mitochondrial ribosomal RNA genes (12S-16S) have been used to estimate the evolutionary tree of the group using different methods of phylogenetic reconstruction. Different competing evolutionary hypotheses have also been compared using the Approximately Unbiased test to further evaluate the robustness of the inferred trees. Results are, in general, consistent with previous studies in recovering the four major lineages of the group (D. virilis phylad, Drosophila montana subphylad, Drosophila kanekoi subphylad and Drosophila littoralis subphylad), although D. kanekoi, D. littoralis and Drosophila ezoana are here inferred to be more closely related to the D. virilis phylad than to the D. montana subphylad. The age of the crown group, estimated with a Bayesian method that assumes a relaxed molecular clock, is placed in the late Miocene (～ 10 Mya). The oldest lineages also appeared during this period (～ 7.5 to ～ 8.9 Mya), while the ages of the basal nodes of the montana subphylad and the virilis phylad are located in the early Pliocene (～ 4.9 and ～ 4.1 Mya). Major cladogenesis events correlate to geological and palaeoclimatic occurrences that most likely affected the freshwater and deciduous forests where these species are found. The inferred biogeographical history of the group, based on the statistical dispersal-vicariance analysis, indicates that the last common ancestor of the group had a Holarctic distribution from which the North American and the Eurasian lineages evolved as a result of a vicariant event.     

Effects of high environmental ammonia on branchial ammonia excretion rates and tissue Rh-protein mRNA expression levels in seawater acclimated Dungeness crab Metacarcinus magister

In the present study of the marine Dungeness crabs Metacarcinus magister, the long term effects of high environmental ammonia (HEA) on hemolymph ammonia and urea concentrations, branchial ammonia excretion rates and mRNA expression levels of the crustacean Rh-like ammonia transporter (RhMM), H(+)-ATPase (subunit B), Na(+)/K(+)-ATPase (α-subunit) and Na(+)/H(+)-exchanger (NHE) were investigated. Under control conditions, the crabs' hemolymph exhibited a total ammonia concentration of 179.3±14.5μmol L(-1), while urea accounted for 467.2±33.5μmol L(-1), respectively. Both anterior and posterior gills were capable of excreting ammonia against a 16-fold inwardly directed gradient. Under control conditions, mRNA expression levels of RhMM were high in the gills in contrast to very low expression levels in all other tissues investigated, including the antennal gland, hepatopancreas, and skeletal muscle. After exposure to 1mmol L(-1) NH(4)Cl, hemolymph ammonia increased within the first 12h to ca. 500μmol L(-1) and crabs were able the keep this hemolymph ammonia level for at least 4 days. During this initial period, branchial RhMM and H(+)-ATPase (subunit B) mRNA expression levels roughly doubled. After 14 days of HEA exposure, hemolymph ammonia raised up to environmental levels, whereas urea levels increased by ca. 30%. At the same time, whole animal ammonia and urea excretion vanished. Additionally, branchial RhMM, H(+)-ATPase, Na(+)/K(+)-ATPase and NHE mRNA levels decreased significantly after long term HEA exposure, whereas expression levels of RhMM in the internal tissues increased substantially. Interestingly, crabs acclimated to HEA showed no mortality even after 4 weeks of HEA exposure. This suggests that M. magister possesses a highly adaptive mechanism to cope with elevated ammonia concentrations in its body fluids, including an up-regulation of an Rh-like ammonia transporter in the internal tissues and excretion or storage of waste nitrogen in a so far unknown form.