Mesodern-inducing factors and mesodermal patterning

Identification of the signalling molecules involved in mesoderm formation in amphibian embryos still presents problems. None of the original candidates, such as activin, have been definitively ruled out, and the new factors, such as the nodal-related genes, have come on to the scene. Of the original candidates, activin has been definitively shown to act as a morphogen, whereas bone morphogenetic protein (BMP)-4 has emerged as a ventral inducer and an inhibitor of neural differentiation. The effects of BMP-4 are antagonized by chordin, a molecule related to the product of the Drosophila gene short gastrulation.     

Epoxiconazole‐Induced Degeneration in Rat Placenta and the Effects of Estradiol Supplementation

Epoxiconazole (CAS‐No. 133855‐98‐8) was recently shown to cause both a marked depletion of maternal estradiol blood levels and a significantly increased incidence of late fetal mortality when administered to pregnant rats throughout gestation (GD 7–18 or 21); estradiol supplementation prevented this epoxiconazole effect in rats (Stinchcombe et al., 2013), indicating that epoxiconazole‐mediated estradiol depletion is a critical key event for induction of late fetal resorptions in rats. For further elucidation of the mode of action, the placentas from these modified prenatal developmental toxicity experiments with 23 and 50 mg/kg bw/d epoxiconazole were subjected to a detailed histopathological examination. This revealed dose‐dependent placental degeneration characterized by cystic dilation of maternal sinuses in the labyrinth, leading to rupture of the interhemal membrane. Concomitant degeneration occurred in the trophospongium. Both placentas supporting live fetuses and late fetal resorptions were affected; the highest degree of severity was observed in placentas with late resorptions. Placental degeneration correlated with a severe decline in maternal serum estradiol concentration. Supplementation with 0.5 and 1.0 μg of the synthetic estrogen estradiol cyclopentylpropionate per day reduced the severity of the degeneration in placentas with live fetuses. The present study demonstrates that both the placental degeneration and the increased incidence of late fetal resorptions are due to decreased levels of estrogen, since estrogen supplementation ameliorates the former and abolishes the latter. Birth Defects Res (Part B) 98:208–221, 2013. © 2013 Wiley Periodicals, Inc.     

Attenuation of pattern recognition receptor signaling is mediated by a MAP kinase kinase kinase

Pattern recognition receptors (PRRs) play a key role in plant and animal innate immunity. PRR binding of their cognate ligand triggers a signaling network and activates an immune response. Activation of PRR signaling must be controlled prior to ligand binding to prevent spurious signaling and immune activation. Flagellin perception in Arabidopsis through FLAGELLIN‐SENSITIVE 2 (FLS2) induces the activation of mitogen‐activated protein kinases (MAPKs) and immunity. However, the precise molecular mechanism that connects activated FLS2 to downstream MAPK cascades remains unknown. Here, we report the identification of a differentially phosphorylated MAP kinase kinase kinase that also interacts with FLS2. Using targeted proteomics and functional analysis, we show that MKKK7 negatively regulates flagellin‐triggered signaling and basal immunity and this requires phosphorylation of MKKK7 on specific serine residues. MKKK7 attenuates MPK6 activity and defense gene expression. Moreover, MKKK7 suppresses the reactive oxygen species burst downstream of FLS2, suggesting that MKKK7‐mediated attenuation of FLS2 signaling occurs through direct modulation of the FLS2 complex.     

Communication,the centrosome and the immunological synapse

Recent findings on the behaviour of the centrosome at the immunological synapse suggest a critical role for centrosome polarization in controlling the communication between immune cells required to generate an effective immune response. The features observed at the immunological synapse show parallels to centrosome (basal body) polarization seen in cilia and flagella, and the cellular communication that is now known to occur at all of these sites.     

Leaf shape variation and herbivore consumption and performance: a case study with Ipomoea hederacea and three generalists

The effect of leaf shape variation on plant-herbivore interactions has primarily been studied from the perspective of host seeking behavior. Yet for leaf shape to affect plant-herbivore coevolution, there must be reciprocal effects of leaf shape variation on herbivore consumption and performance. We investigated whether alternative leaf morphs affected the performance of three generalist insect herbivores by taking advantage of a genetic polymorphism and developmental plasticity in leaf shape in the Ivyleaf morning glory, Ipomoea hederacea. Across four experiments, we found variable support for an effect of leaf shape genotype on insects. For cabbage loopers (Trichoplusia ni) and corn earworms (Helicoverpa zea) we found opposing, non-significant trends: T. ni gained more biomass on lobed genotypes, while H. zea gained more biomass on heart-shaped genotypes. For army beetworms (Spodoptera exigua), the effects of leaf shape genotype differed depending on the age of the plants and photoperiod of growing conditions. Caterpillars feeding on tissue from older plants (95 days) grown under long day photoperiods had significantly greater consumption, dry biomass, and digestive efficiency on lobed genotypes. In contrast, there were no significant differences between heart-shaped and lobed genotypes for caterpillars feeding on tissue from younger plants (50 days) grown under short day photoperiods. For plants grown under short days, we found that S. exigua consumed significantly less leaf area when feeding on mature leaves than juvenile leaves, regardless of leaf shape genotype. Taken together, our results suggest that the effects of leaf shape variation on insect performance are likely to vary between insect species, growth conditions of the plant, and the developmental stage and age of leaves sampled. Handling editor: May Berenbaum.     

A highly conserved nuclear gene for low-level phylogenetics: elongation factor-1 alpha recovers morphology-based tree for heliothine moths

Molecular systematists need increased access to nuclear genes. Highly conserved, low copy number protein-encoding nuclear genes have attractive features for phylogenetic inference but have heretofore been applied mostly to very ancient divergences. By virtue of their synonymous substitutions, such genes should contain a wealth of information about lower-level taxonomic relationships as well, with the advantage that amino acid conservatism makes both alignment and primer definition straightforward. We tested this postulate for the elongation factor-1 alpha (EF-1 alpha) gene in the noctuid moth subfamily Heliothinae, which has probably diversified since the middle Tertiary. We sequenced 1,240 bp in 18 taxa representing heliothine groupings strongly supported by previous morphological and allozyme studies. The single most parsimonious gene tree and the neighbor-joining tree for all nucleotides show almost complete concordance with the morphological tree. Homoplasy and pairwise divergence levels are low, transition/transversion ratios are high, and phylogenetic information is spread evenly across gene regions. The EF-1 alpha gene and presumably other highly conserved genes hold much promise for phylogenetics of Tertiary age eukaryote groups.      

Costs and benefits of cold tolerance in transgenic Arabidopsis thaliana

Cold tolerance in plants is an ecologically important trait that has been under intensive study for basic and applied reasons. Determining the fitness benefits and costs of cold tolerance has previously been difficult because cold tolerance is normally an induced trait that is not expressed in warm environments. The recent creation of transgenic plants constitutively expressing cold tolerance genes enables the investigation of the fitness consequences of cold tolerance in multiple temperature environments. We studied three genes from the CBF (C-repeat/dehydration responsive element binding factor) cold tolerance pathway, CBF1, 2 and 3, in Arabidopsis thaliana to test for benefits and costs of constitutive cold tolerance. We used multiple insertion lines for each transgene and grew the lines in cold and control conditions. Costs of cold tolerance, as determined by fruit number, varied by individual transgene. CBF2 and 3 overexpressers showed costs of cold tolerance, and no fitness benefits, in both environments. CBF1 overexpressing plants showed no fitness cost of cold tolerance in the control environment and showed a marginal fitness benefit in the cold environment. These results suggest that constitutive expression of traits that are normally induced in response to environmental stress will not always lead to costs in the absence of that stress, and that the ecological risks of CBF transgene escape should be assessed prior to their use in commercial agriculture.