Legumes symbioses: absence of Nod genes in photosynthetic bradyrhizobia

Leguminous plants (such as peas and soybeans) and rhizobial soil bacteria are symbiotic partners that communicate through molecular signaling pathways, resulting in the formation of nodules on legume roots and occasionally stems that house nitrogen-fixing bacteria. Nodule formation has been assumed to be exclusively initiated by the binding of bacterial, host-specific lipochito-oligosaccharidic Nod factors, encoded by the nodABC genes, to kinase-like receptors of the plant. Here we show by complete genome sequencing of two symbiotic, photosynthetic, Bradyrhizobium strains, BTAi1 and ORS278, that canonical nodABC genes and typical lipochito-oligosaccharidic Nod factors are not required for symbiosis in some legumes. Mutational analyses indicated that these unique rhizobia use an alternative pathway to initiate symbioses, where a purine derivative may play a key role in triggering nodule formation.     

Development of a Potato Cultivar (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.) Core Collection,a Valuable Tool to Prospect Genetic Variation for Novel Traits

This study presents the development of a core collection capturing the genetic diversity of a collection of 350 tetraploid cultivated potato varieties (Solanum tuberosum L.). The core collection was established by using simple sequence repeats (SSR) data and the M strategy, which aims at maximizing the allelic diversity. A 48-core collection was defined which captured 99.5% of the SSR alleles used to establish it, and 96.9% of the SSR alleles which belonged to an independent set of markers. The defined core collection was further validated by analysing 35 agro-morphological traits. The class coverage value and the estimates of the Shannon-Weaver diversity index indicated a good representation of the phenotypic diversity in the core collection. Furthermore, the core set included accessions having the most desirable status for several agronomic traits. A linkage disequilibrium (LD) analysis, using data obtained with the SolCAP SNP array on the defined core collection, was performed. The population structure analysis showed that the core collection did not present a clear genetic structure. The linkage disequilibrium analysis carried out between markers located on the same pseudomolecule within 10,000 bp concluded that 41.3% of these pairs of SNP markers have a significant LD. We conclude that this core collection, representative of the genetic diversity of cultivated potato varieties, is a relevant tool for a first screening for genetic variation regarding novel traits of interest.     

Retention and bioaccessibility of β-carotene in blended foods containing orange-fleshed sweet potato flour

The retention and bioaccessibility of β-carotene (BC) in blended foods made with part orange-fleshed sweet potato (OFSP) flour (30%) were examined. Chapatis and porridges were prepared by local processors under field conditions (FC) in Uganda (n=10). While the retention of all-trans-BC in porridges (69 to 93%) and chapatis (70 to 97%) varied between the processors, there was no overall difference between the two products and this was probably because of the variability in FC. BC retention in mandazis was similar to that of chapatis and porridges. Processing in FC significantly increased the amount of cis-isomers, in particular 13-cis-BC. The bioaccessibility of the BC as measured by their transfer into micelles was evaluated using an in vitro digestion procedure in various OFSP-derived products. After in vitro digestion, the percentage of micellarized all-trans-BC was greater in products cooked with oil, chapati (73%) and mandazi (49%), as compared with the boiled ones, porridge (16%) and pure?ed from boiled root (10%). In all the products, the incorporation into micelles for 13-cis-BC was significantly higher to that of all-trans-BC. When taking into account the bioaccessibility of all-trans-BC and 13-cis-BC isomer, an edible portion of porridge (one mug), boiled root (half a root), mandazis (two), or chapati (one) could provide a significant part of the daily vitamin A requirements of a child under 6 years (respectively 20, 46, 75, or 100%). These data support the promotion/consumption of locally cooked OFSP food products to tackle vitamin A deficiency in sub-Saharan Africa.     

An in planta, Agrobacterium-mediated transient gene expression method for inducing gene silencing in rice (Oryza sativa L.) leaves

Background

Although the genetic structure of rice germplasm has been characterized worldwide, few studies investigated germplasm from Thailand, the world’s largest exporter of rice. Thailand and the International Rice Research Institute (IRRI) have diverse collections of rice germplasm, which could be used to develop breeding lines with desirable traits. This study aimed to investigate the level of genetic diversity and structures of Thai and selected IRRI germplasm. Understanding the genetic structure and relationships among these germplasm will be useful for parent selection used in rice breeding programs.

Results

From the 98 InDel markers tested for single copy and polymorphism, 19 markers were used to evaluate 43 Thai and 57 IRRI germplasm, including improved cultivars, breeding lines, landraces, and 5 other Oryza species. The Thai accessions were selected from all rice ecologies such as irrigated, deep water, upland, and rainfed lowland ecosystems. The IRRI accessions were groups of germplasm having agronomic desirable traits, including temperature-sensitive genetic male sterility (TGMS), new plant type, early flowering, and biotic and abiotic stress resistances. Most of the InDel markers were genes with diverse functions. These markers produced the total of 127 alleles for all loci, with a mean of 6.68 alleles per locus, and a mean Polymorphic Information Content (PIC) of 0.440. Genetic diversity of Thai rice were 0.3665, 0.4479 and 0.3972 for improved cultivars, breeding lines, and landraces, respectively, while genetic diversity of IRRI improved and breeding lines were 0.3272 and 0.2970, respectively. Cluster, structure, and differentiation analyses showed six distinct groups: japonica, TGMS, deep-water, IRRI germplasm, Thai landraces and breeding lines, and other Oryza species.

Conclusions

Thai and IRRI germplasm were significantly different. Thus, they can be used to broaden the genetic base and trait improvements. Cluster, structure, and differentiation analyses showed concordant results having six distinct groups, in agreement with their development, and ecologies.     

Dairy goat demography and Q fever infection dynamics

Between 2007 and 2009, the largest human Q fever epidemic ever described occurred in the Netherlands. The source was traced back to dairy goat farms, where abortion storms had been observed since 2005. Since one putative cause of these abortion storms is the intensive husbandry systems in which the goats are kept, the objective of this study was to assess whether these could be explained by herd size, reproductive pattern and other demographic aspects of Dutch dairy goat herds alone. We adapted an existing, fully parameterized simulation model for Q fever transmission in French dairy cattle herds to represent the demographics typical for Dutch dairy goat herds. The original model represents the infection dynamics in a herd of 50 dairy cows after introduction of a single infected animal; the adapted model has 770 dairy goats. For a full comparison, herds of 770 cows and 50 goats were also modeled. The effects of herd size and goat versus cattle demographics on the probability of and time to extinction of the infection, environmental bacterial load and abortion rate were studied by simulation. The abortion storms could not be fully explained by demographics alone. Adequate data were lacking at the moment to attribute the difference to characteristics of the pathogen, host, within-herd environment, or a combination thereof. The probability of extinction was higher in goat herds than in cattle herds of the same size. The environmental contamination was highest within cattle herds, which may be taken into account when enlarging cattle farming systems.     

The relationship of host-mediated induced resistance to polymorphism in gene-for-gene relationships

Gene-for-gene relationships are a common feature of plant-parasite interactions. Polymorphism at host resistance and parasite avirulence loci is maintained if there is negative, direct frequency-dependent selection on alleles of either gene. More specifically, selection of this kind is generated when the disease is polycyclic with frequent auto-infection. When an incompatible interaction occurs between a resistant host and an avirulent parasite, systemic defenses are triggered, rendering the plant more resistant to a later attack by another parasite. However, induced resistance (IR) incurs a fitness cost to the plant. Here, the effect of IR on polymorphism in gene-for-gene interactions is investigated. First, in an infinite population model in which parasites have two generations per host generation, increasing the fitness cost of IR increases selection for susceptible plants at low disease severity, while increasing the effectiveness of IR against further parasite attacks enhances selection for resistant plants at high disease severity. This reduces the possibility of polymorphism being maintained in host and parasite populations. In finite population models, the number of plants varies over time as a function of the disease burden of the population. Polymorphism in gene-for-gene relationships is then more stable at high disease prevalence and severity if IR reactions are more costly when there is competition for resources between plants.     

人为污染土壤中Cd、Pb、和Zn的化学有效性：地球化学反应与口服生物有效性评价

The most recent in vitro tests used to determine metal bioaccessiblility are generally time-consuming and expensive.This study aimed at determining potential relationships between the concentrations of metals extracted using single-extraction methods and the concentrations of bioaccessible metals assessed by a harmonised in vitro test,the Unified BARGE Method (UBM).A total number of 27 soil samples were collected from kitchen gardens and lawns with various physicochemical parameters and contamination levels.Significant relationships were obtained between Cd,Pb and Zn extracted in gastric and gastrointestinal phases and using single extractions.The best relationhips were established using acetic and citric acids for Cd,whereas for Pb,citric acid and ethylenediaminetetraacetic acid (EDTA) were identified as the best extractants.These relationships were improved by means of a linear multiple regression with a downward stepwise procedure involving agronomic parameters (soil cation exchange capacity and assimilated P).This method highlighted the fact that the cation exchange capacity and P contents in soils were the two main parameters that controlled the human bioaccessibility of Cd,Pb and Zn in the gastric phase.Besides,the metal concentrations extracted with the acetic and citric acids correlated well with the metal concentrations in the gastric and gastrointestinal phases,suggesting that the bioaccessible metals were mainly in a soluble form,weakly bound to the organic matter and associated with the carbonates and the Fe and Mn oxides/hydroxides in soils.     

Chemical constituents from Tillandsia recurvata

The CHCl3 extract of Tillandsia recurvata yielded 5,3'-dihydroxy-6,7,8,4'-tetramethoxyflavanone (1), 1,3-di-O-cinnamoyl-glycerol (2) and ethyl ester of caffeic acid. Their structures were elucidated by means of spectroscopic methods such as mass spectroscopy and 1 and 2D-NMR.     

Influence of landscape and time of year on bat-wind turbines collision risks

Landscape Ecology - Collisions with wind turbines threaten bat populations worldwide. Previous studies tried to assess the effects of landscape on mortalities. Yet, the count of carcasses found per...