Variations in bulk leaf carbon isotope discrimination, growth and related leaf traits among three Populus nigra L. populations

The ongoing global change could be an additional threat to the establishment and the long-term survival of Populus nigra L., an emblematic European riparian species. With the general aim of gaining insights into the adaptive potential of this species, we (i) quantified variations within and among three French P. nigra populations for key physiological attributes, i.e., water-use efficiency (assessed from bulk leaf carbon isotope discrimination, Δ(13)C), growth performance and related leaf traits, (ii) examined genotype and population by environment interactions, and (iii) explored the relationship between Δ(13)C and growth. Thirty genotypes were sampled in each of three naturally established populations and grown in two different sites, Orléans (ORL) and Guémené-Penfao (GMN). In ORL, two similar plots were established and different watering regimes were applied in order to test for the drought response. Significant variations were observed for all traits within and among populations irrespective of site and watering. Trait variation was larger within than among populations. The effect of drought was neither genotype- nor population-dependent, contrary to the effect of site. The population ranking was maintained in all sites and watering regimes for the two most complex traits: Δ(13)C and growth. Moreover, these two traits were unrelated, which indicates that (i) water-use efficiency and growth are largely uncoupled in this species, and (ii) the environmental factors driving genetic structuration for Δ(13)C and growth act independently. The large variations found within populations combined with the consistent differences among populations suggest a large adaptive potential for P. nigra.     

Excitation energy partitioning and quenching during cold acclimation in Scots pine

We studied the influence of two irradiances on cold acclimation and recovery of photosynthesis in Scots pine (Pinus sylvestris L.) seedlings to assess mechanisms for quenching the excess energy captured by the photosynthetic apparatus. A shift in temperature from 20 to 5 degrees C caused a greater decrease in photosynthetic activity, measured by chlorophyll fluorescence and oxygen evolution, in plants exposed to moderate light (350 micromol m(-2) s(-1)) than in shaded plants (50 micromol m(-2) s(-1)). In response to the temperature shift, maximal photochemical efficiency of photosystem II (PSII), measured as the ratio of variable to maximal chlorophyll fluorescence (Fv/Fm) of dark-adapted samples, decreased to 70% in exposed seedlings, whereas shaded seedlings maintained Fv/Fm close to initial values. After a further temperature decrease to -5 degrees C, only 8% of initial Fv/Fm remained in exposed plants, whereas shaded plants retained 40% of initial Fv/Fm. Seven days after transfer from -5 to 20 degrees C, recovery of photochemical efficiency was more complete in the shaded plants than in the exposed plants (87 and 65% of the initial Fv/Fm value, respectively). In response to cold stress, the estimated functional absorption cross section per remaining PSII reaction center increased at both irradiances, but the increase was more pronounced in exposed seedlings. Estimates of energy partitioning in the needles showed a much higher dissipative component in the exposed seedlings at low temperatures, pointing to stronger development of non-photochemical quenching at moderate irradiances. The de-epoxidation state of the xanthophyll cycle pigments increased in exposed seedlings at 5 degrees C, contributing to the quenching capacity, whereas significant de-epoxidation in the shaded plants was observed only when temperatures decreased to -5 degrees C. Thermoluminescence (TL) measurements of PSII revealed that charge recombinations between the second oxidation state of Mn-cluster S2 and the semireduced secondary electron acceptor quinone Q(B)- (S2Q(B)-) were shifted to lower temperatures in cold-acclimated seedlings compared with control seedlings and this effect depended on irradiance. Concomitant with this, cold-acclimated seedlings demonstrated a significant shift in the S2 recombination with primary acceptor Q(A)- (S2Q(A)-) characteristic TL emission peak to higher temperatures, thus narrowing the redox potential gap between S2Q(B)- and S2Q(A)-, which might result in increased probability for non-radiative radical pair recombination between the PSII reaction center chlorophyll a (P680+) and Q(A)- (P680+)Q(A)-) (reaction center quenching) in cold-acclimated seedlings. In Scots pine seedlings, mechanisms of quenching excess light energy in winter therefore involve light-dependent regulation of reaction center content and both reaction center-based and antenna-based quenching of excess light energy, enabling them to withstand high excitation pressure under northern winter conditions.     

Structure of Galphaq-p63RhoGEF-RhoA complex reveals a pathway for the activation of RhoA by GPCRs

The guanine nucleotide exchange factor p63RhoGEF is an effector of the heterotrimeric guanine nucleotide-binding protein (G protein) Galphaq and thereby links Galphaq-coupled receptors (GPCRs) to the activation of the small-molecular-weight G protein RhoA. We determined the crystal structure of the Galphaq-p63RhoGEF-RhoA complex, detailing the interactions of Galphaq with the Dbl and pleckstrin homology (DH and PH) domains of p63RhoGEF. These interactions involve the effector-binding site and the C-terminal region of Galphaq and appear to relieve autoinhibition of the catalytic DH domain by the PH domain. Trio, Duet, and p63RhoGEF are shown to constitute a family of Galphaq effectors that appear to activate RhoA both in vitro and in intact cells. We propose that this structure represents the crux of an ancient signal transduction pathway that is expected to be important in an array of physiological processes.     

Citrobacter freundii septicemia in two dogs.

A 4-month-old Maltese puppy and a 7.5-year-old Collie were diagnosed with septicemia associated with Citrobacter freundii. The puppy died soon, after developing weakness and mucohemorragic diarrhea. The Collie had immune-mediated hemolytic anemia and thrombocytopenia and was treated with immunosuppressive drugs before being euthanized. Gross examination of the puppy revealed mucohemorrhagic intestinal contents. Focal necrotic hepatitis, fibrinous peritonitis, interstitial pneumonia, and hemorrhagic gastrointestinal contents were observed in the older dog. Histologically, there was a diffuse, moderate, histiocytic meningitis in the puppy and a focal fibrinonecrotic hepatitis in the adult dog. Lesions in both dogs contained numerous gram-negative rods. Citrobacter freudii is a potential cause of monomicrobic bacteraemia-septicemia in puppies or immunocompromized adult dogs.The gastrointestinal tract is probably the main site of entry.     

Growth performance of hybrid striped bass (Morone chrysops × M. saxatilis) fed with commercial pike perch and trout diets

Two commercial trout diets (Oncorhynchus mykiss) and one commercial pike perch diet (Sander lucioperca) were fed to hybrid striped bass (Morone chrysops × M. saxatilis) (mean initial weight ± SD of 60.7 g ± 12.1; mean initial length SD of 17.2 cm ± 1.1) for 69 days at rations of approximately 1% average body weight. While final body weight (FBW), final length (FBL) and condition factor (Cf) were not significantly influenced by diets, specific growth rate (SGR) in hybrid striped bass fed with the pike perch diet (1.15) was significantly higher than those fed with either of the two trout diets (1.04 and 1.07). The feed conversion ratio (FCR) in hybrid striped bass fed with the pike perch diet (1.0) was significantly lower than the FCR in hybrid striped bass fed with either of the two trout diets (1.1 and 1.2). When hybrid striped bass (mean initial body weight: 65.7 ± 4.5 and 127.7 ± 2.9 g) were fed with the pike perch diet twice per day until satiation for 52 days, the SGR was 1.7 and 1.15% d^?1 in fishes with an average body weight of 116 and 183 g, respectively. Present results demonstrate that growth performance in hybrid striped bass can be improved when fishes are fed with commercial pike perch diets rather than using commercial trout diets as is the current practice.

     

Progress in Mapping and Cloning Qualitative and Quantitative Resistance Against <Emphasis Type="Italic">Phytophthora infestans</Emphasis> in Potato and Its Wild Relatives

Cultivated potato is susceptible to many pests and pathogens, none of which is more of a threat to potato agriculture than the late blight disease, caused by the oomycete Phytophthora infestans (Mont.) de Bary. To date all efforts to thwart this most adaptive of pathogens have failed, and early attempts to deploy ‘R genes’ introgressed from the wild Mexican hexaploid Solanum demissum ended in abject failure. With the advent of facile gene mapping and cloning, allied to knowledge of plant resistance gene structure, renewed efforts are leading to mapping and isolation of new sources of late blight resistance in potato wild species, many of which are being performed under the auspices of the BIOEXPLOIT project (Sub-project 2). We document recent advances in late blight resistance gene mapping and isolation, and postulate how these genes, allied to knowledge of pathogen effectors and their recognition specificity, may greatly enhance our chances of halting the progress of late blight disease in potato crops worldwide.     

The genome of the African trypanosome Trypanosoma brucei

African trypanosomes cause human sleeping sickness and livestock trypanosomiasis in sub-Saharan Africa. We present the sequence and analysis of the 11 megabase-sized chromosomes of Trypanosoma brucei. The 26-megabase genome contains 9068 predicted genes, including approximately 900 pseudogenes and approximately 1700 T. brucei-specific genes. Large subtelomeric arrays contain an archive of 806 variant surface glycoprotein (VSG) genes used by the parasite to evade the mammalian immune system. Most VSG genes are pseudogenes, which may be used to generate expressed mosaic genes by ectopic recombination. Comparisons of the cytoskeleton and endocytic trafficking systems with those of humans and other eukaryotic organisms reveal major differences. A comparison of metabolic pathways encoded by the genomes of T. brucei, T. cruzi, and Leishmania major reveals the least overall metabolic capability in T. brucei and the greatest in L. major. Horizontal transfer of genes of bacterial origin has contributed to some of the metabolic differences in these parasites, and a number of novel potential drug targets have been identified.     

Atypical myopathy in 2 Bactrian camels

Atypical myopathy (AM) is an acute seasonal rhabdomyolysis seen primarily in equids, caused by the ingestion of sycamore maple samaras containing hypoglycin A (HGA) and methylenecyclopropyl-glycine (MCPG). Toxic metabolites inhibit acyl-CoA dehydrogenases and enoyl-CoA hydratases, causing selective hyaline degeneration of type I muscle fibers. Two zoo-kept Bactrian camels (Camelus bactrianus) with a fatal course of AM had sudden onset of muscle pain and weakness, recumbency, and dysphagia, accompanied by increased serum creatine kinase activity and detection in serum of HGA, MCPG, and metabolites. Medical treatment was ineffective. At postmortem examination, sycamore maple tree material was found within the first gastric compartment of the 2-y-old gelding. Although musculature was macroscopically normal, histologically, monophasic hyaline degeneration was marked within type I fibers of intercostal and hypoglossal muscles of the gelding, and in neck, tongue, and masticatory muscles of the cow. The ingestion of sycamore maple material can cause AM in Bactrian camels, and trees of the Sapindaceae family should be avoided in enclosures.     

First occurrence of resistance to strobilurin fungicides in Microdochium nivale and Microdochium majus from French naturally infected wheat grains

BACKGROUND: Microdochium nivale (Fr.) Samuels & Hallet and Microdochium majus (Wollenweber) belong to the Fusarium ear blight (FEB) fungal complex affecting cereals. In 2007 and 2008, major Microdochium sp. infestations were observed in France, and the efficacy of strobilurins was found to be altered in some field trials. The aim of this study was to determine the sensitivity to strobilurins of French isolates of Microdochium and to characterise the possible mechanisms of resistance. RESULTS: Half of the strains collected in 2007 were resistant to strobilurins, and most also displayed strong resistance to benzimidazoles. Strobilurin resistance was found mostly in M. majus isolates. Positive cross‐resistance was observed between all strobilurins tested, but not with the phenylpyrrole derivative fludioxonil and the various classes of sterol biosynthesis inhibitors (SBIs). In most strains, resistance was correlated with the G143A substitution in cytochrome b, the molecular target of strobilurins. Two other mechanisms were also detected at lower frequencies. CONCLUSION: This is the first report of strobilurin resistance in Microdochium. Several resistance mechanisms have evolved independently in populations and may have different impacts on field efficacy. This makes the accurate detection and quantification of QoI resistance difficult. The management of field resistance and efficacy must be adapted to take these findings into account. Copyright © 2009 Society of Chemical Industry     

Genome of the host-cell transforming parasite Theileria annulata compared with T. parva

Theileria annulata and T. parva are closely related protozoan parasites that cause lymphoproliferative diseases of cattle. We sequenced the genome of T. annulata and compared it with that of T. parva to understand the mechanisms underlying transformation and tropism. Despite high conservation of gene sequences and synteny, the analysis reveals unequally expanded gene families and species-specific genes. We also identify divergent families of putative secreted polypeptides that may reduce immune recognition, candidate regulators of host-cell transformation, and a Theileria-specific protein domain [frequently associated in Theileria (FAINT)] present in a large number of secreted proteins.