Burkholderia phytofirmans PsJN acclimates grapevine to cold by modulating carbohydrate metabolism

Low temperatures damage many temperate crops, including grapevine, which, when exposed to chilling, can be affected by symptoms ranging from reduced yield up to complete infertility. We have previously demonstrated that Burkholderia phytofirmans PsJN, a plant growth-promoting rhizobacteria (PGPR) that colonizes grapevine, is able to reduce chilling-induced damage. We hypothesized that the induced tolerance may be explained at least partly by the impact of bacteria on grapevine photosynthesis or carbohydrate metabolism during cold acclimation. To investigate this hypothesis, we monitored herein the fluctuations of photosynthesis parameters (net photosynthesis [P(n)], intercellular CO(2) concentration, stomatal conductances, ΦPSII, and total chlorophyll concentration), starch, soluble sugars (glucose, fructose, saccharose, mannose, raffinose, and maltose), and their precursors during 5 days of chilling exposure (4°C) on grapevine plantlets. Bacterization affects photosynthesis in a non-stomatal dependent pattern and reduced long-term impact of chilling on P(n). Furthermore, all studied carbohydrates known to be involved in cold stress tolerance accumulate in non-chilled bacterized plantlets, although some of them remained more concentrated in the latter after chilling exposure. Overall, our results suggest that modification of carbohydrate metabolism in bacterized grapevine plantlets may be one of the major effects by which this PGPR reduces chilling-induced damage.     

Different biogeographic patterns of prokaryotes and microbial eukaryotes in epilithic biofilms

Microbial biogeography studies expend much effort in determining whether environmental selection or stochastic processes related to dispersal are more important in shaping community composition. While both types of factors are possibly influential, it is tacitly assumed that protists, or microbial eukaryotes in general, behave biogeographically as prokaryotes because of their small physical size. However, direct evidence for this in exactly the same environment and at the same phylogenetic depth is lacking. In this study, we compared the structure of both prokaryotic and eukaryotic components of microbial communities forming biofilms on mineral substrates in different geographic locations at the level of small-subunit (SSU) rRNA-based operational taxonomic units (OTUs). These microbial communities are subjected to strong environmental selection and contain significant proportions of extremophilic microorganisms adapted to desiccation and UV radiation. We find that the nature of the substrate as well as climatic variables and geography influences microbial community structure. However, constrained correspondence analyses and distance-decay curves showed that, whereas the substrate type was the most significant factor structuring bacterial communities, geographic location was the most influential factor for microbial eukaryote communities. Biological explanations implying a higher dispersal success for bacteria combined with more mobile lifestyles for predatory protists may underlie these different prokaryote versus microbial eukaryote biogeographic patterns.     

Benzoylbenzimidazole-based selective inhibitors targeting Cryptosporidium parvum and Toxoplasma gondii calcium-dependent protein kinase-1

Calcium-dependent protein kinase-1 (CDPK1) from Cryptosporidium parvum (CpCDPK1) and Toxoplasma gondii (TgCDPK1) have become attractive targets for discovering selective inhibitors to combat infections caused by these protozoa. We used structure-based design to improve a series of benzoylbenzimidazole-based compounds in terms of solubility, selectivity, and potency against CpCDPK1 and TgCDPK1. The best inhibitors show inhibitory potencies below 50nM and selectivity well above 200-fold over two human kinases with small gatekeeper residues.     

Pregnancy reduces RhoA/Rho kinase and protein kinase C signaling pathways downstream of thromboxane receptor activation in the rat uterine artery

During pregnancy, reduced vascular responses to constrictors contribute to decreased uterine and total vascular resistance. Thromboxane A(2) (TxA(2)) is a potent vasoconstrictor that exerts its actions via diverse signaling pathways, and its biosynthesis increases in preeclampsia. In this study, we hypothesized that maternal vascular responses to TxA(2) will be attenuated via Rho kinase, PKC, p38 MAPK, and ERK1/2 signaling pathways. Isolated ring segments of uterine and small mesenteric arteries from late pregnant (19-21 days) and virgin rats were suspended in a myograph, and isometric force was measured. Pregnancy did not affect uterine and mesenteric artery responses to the TxA(2) analog U-46619 (10(-9)-10(-5) M), but transduction signals associated with these contractions were different between pregnant and nonpregnant rats. Inhibition of Rho kinase (10(-6) M Y-27632) reduced sensitivity to U-46619 in virgin uterine vessels but did not inhibit these contractions in pregnant uterine arteries and had no effect on mesenteric vessels. Treatment of arterial segments with a PKC inhibitor (10(-6) M bisindolylmaleimide I) reduced U-46619-induced contractions in virgin uterine and mesenteric arteries and in pregnant mesenteric arteries. Pregnant uterine arteries, however, were unresponsive to PKC inhibition. Inhibition of ERK1/2 (10(-5) M PD-98059) and p38 MAPK (10(-5) M SB-203580) reduced U46619-induced contractions in nonpregnant vessels and in pregnant uterine and mesenteric vessels. These data suggest that normal pregnancy does not affect uterine and mesenteric contractile responses to TxA(2) but reduces the contribution of Rho kinase and PKC signaling pathways to these contractions in the uterine vasculature. In contrast, the role of ERK1/2 and p38 MAPK in U-46619-induced uterine contractions remains unchanged with pregnancy. TxA(2)-associated transduction signals and its regulators might present potential targets for the development of new treatments for preeclampsia and other pregnancy-associated vascular diseases.     

Dosage compensation in birds

The Z and W sex chromosomes of birds have evolved independently from the mammalian X and Y chromosomes [1]. Unlike mammals, female birds are heterogametic (ZW), while males are homogametic (ZZ). Therefore male birds, like female mammals, carry a double dose of sex-linked genes relative to the other sex. Other animals with nonhomologous sex chromosomes possess "dosage compensation" systems to equalize the expression of sex-linked genes. Dosage compensation occurs in animals as diverse as mammals, insects, and nematodes, although the mechanisms involved differ profoundly [2]. In birds, however, it is widely accepted that dosage compensation does not occur [3-5], and the differential expression of Z-linked genes has been suggested to underlie the avian sex-determination mechanism [6]. Here we show equivalent expression of at least six of nine Z chromosome genes in male and female chick embryos by using real-time quantitative PCR [7]. Only the Z-linked ScII gene, whose ortholog in Caenorhabditis elegans plays a crucial role in dosage compensation [8], escapes compensation by this assay. Our results imply that the majority of Z-linked genes in the chicken are dosage compensated.     

Molecular Evidence for Gender Differences in the Migratory Behaviour of a Small Seabird

Molecular sexing revealed an unexpectedly strong female bias in the sex ratio of pre-breeding European Storm Petrels (Hydrobates pelagicus), attracted to playback of conspecific calls during their northwards migration past SW Europe. This bias was consistent across seven years, ranging from 80.8% to 89.7% female (mean annual sex ratio ± SD = 85.5% female ±4.1%). The sex ratio did not differ significantly from unity (i.e., 50% female) among (i) Storm Petrel chicks at a breeding colony in NW France, (ii) adults found dead on beaches in Southern Portugal, (iii) breeding birds attending nest burrows in the UK, captured by hand, and (iv) adults captured near a breeding colony in the UK using copies of the same sound recordings as used in Southern Europe, indicating that females are not inherently more strongly attracted to playback calls than males. A morphological discriminant function analysis failed to provide a good separation of the sexes, showing the importance of molecular sexing for this species. We found no sex difference in the seasonal or nocturnal timing of migration past Southern Europe, but there was a significant tendency for birds to be caught in sex-specific aggregations. The preponderance of females captured in Southern Europe suggests that the sexes may differ in migration route or in their colony-prospecting behaviour during migration, at sites far away from their natal colonies. Such differences in migration behaviour between males and females are poorly understood but have implications for the vulnerability of seabirds to pollution and environmental change at sea during the non-breeding season.     

From Desert to Rainforest: Phenotypic Variation in Functionally Important Traits of Bushy-Tailed Woodrats (Neotoma cinerea) Across Two Climatic Extremes

Changes in body size inversely related to ambient temperatures have been described in woodrats (Neotoma) over time scales ranging from decades to millennia. However, climate-mediated variation in other traits has not been evaluated, and the effects of precipitation have been overlooked. We assessed variation in skull morphology among bushy-tailed woodrats (Neotoma cinerea) over two sampling transects spanning coastal rainforest and interior desert environments to determine whether skull morphology varied with climate. We also tested whether previously described size-temperature relationships could be generalized to our study populations. In both transects, linear measurements of functionally significant traits differed between coastal and interior populations. Geometric morphometric analyses of shape confirmed some of those differences and revealed additional patterns of skull variation. Variation in some linear measurements, including body size, was predicted by climate. However, body and skull size, as well as measurements of skull components, displayed varying responses. Although longitudinal patterns of body size variation supported Bergmann’s rule, skull size variation was only weakly associated with climate. The strongest phenotypic responses to climate were those of auditory, dental, and palatal skull traits. Altogether, our findings suggest that geographic variation in temperature and precipitation mediated selective heterogeneity and plasticity in skull traits associated with food processing and sensory organs in N. cinerea. This was consistent with our expectation of resource-dependent phenotypic variation among populations in environments with highly contrasting climatic regimes.     

Crystal structure of firefly luciferase in a second catalytic conformation supports a domain alternation mechanism

Beetle luciferases catalyze a two-step reaction that includes the initial adenylation of the luciferin substrate, followed by an oxidative decarboxylation that ultimately produces light. Evidence for homologous acyl-CoA synthetases supports a domain alternation catalytic mechanism in which these enzymes' C-terminal domain rotates by ～140° to adopt two conformations that are used to catalyze the two partial reactions. While many structures exist of acyl-CoA synthetases in both conformations, to date only biochemical evidence supports domain alternation with luciferase. We have determined the structure of a cross-linked luciferase enzyme that is trapped in the second conformation. This new structure supports the role of the second catalytic conformation and provides insights into the biochemical mechanism of the luciferase oxidative step.