Specific binding of basic fibroblast growth factor to basement membrane-like structures and to purified heparan sulfate proteoglycan of the EHS tumor

The binding of iodinated basic fibroblast growth factor (bFGF) to low-density heparan sulfate proteoglycan purified from the Engelbreth Holm Swarm (EHS) sarcoma was investigated using different techniques. The tumor clearly contained bFGF, the level being comparable to that found in other tissues such as human or bovine brain. 125I bFGF strongly bound to the basement membrane-like matrix of EHS frozen sections as revealed by autoradiography. Iodinated bFGF bound to purified heparan sulfate proteoglycan but not to laminin or collagen type IV, three components isolated from the same tumor. In contrast, acidic fibroblast growth factor (aFGF) displayed negligible binding to heparan sulfate proteoglycan. Binding of bFGF to frozen sections and to purified proteoglycan could be strongly inhibited by heparin and was displaced by an excess of unlabeled factor and completely suppressed after heparitinase and heparinase treatments. Binding was a function of the salt concentration and was abolished at 0.6 M NaCl. Scatchard analysis indicated the affinity site had a Kd of about 30 nM, a value 10-15 higher than that recently reported by Moscatelli (J. Cell. Physiol., 131:123-130, 1987) in the case of the low-affinity binding sites present on the surface of baby hamster kidney (BHK) cells.     

The cost of herbicide resistance in white-chicory: ecological implications for its commercial release

Applications for the commercial release of herbicide-resistant crops, most of them transgenic, are likely to become more frequent in the coming years. The ecological concerns raised by their large scale use call for risk-assessment studies. One of the major issues in such studies is the relative fitness of the resistant line compared to the susceptible when no herbicide is applied since this will largely determine the long-term fate of the resistance gene outside of the field. Here we report on a comparison of a sulfonylurea-resistant line of white-chicory regenerated from a non-mutagenized cell culture with a supposedly isogenic susceptible biotype. The plants were grown in experimental plots at a range of densities in a replacement series. The reproductive output of the plants decreased with increasing density but no significant difference was found between the two lines for any vegetative or reproductive trait at any density. This suggests that no cost is associated with the mutation causing the resistance and that the resistance gene would not be selected against if it escaped to populations of wild chicories.     

Behavioral adaptations of two phytophagous insects feeding on two species of phototoxic Asteraceae

Two phototoxic plants of the Asteraceae family were studied in relation to species of phytophagous insects for which they are hosts:Argyrotaenia velutinana Wlk. feeding onChrysanthemum leucanthemum L. andChlorochlamys chloroleucaria (Guenée) colonizingRudbeckia hirta L. The toxicity of these two plants is related to the presence of acetylenes and thiophenes that induce a light-mediated production of deleterious singlet oxygen and other free radicals (phototoxicity). Results showed that females ofA. velutinana laid their eggs preferentially in the shade and the larvae adopted hiding behaviors, such as bending of ligulate corollas and silk spinning to build opaque shelters. By avoiding direct exposure to the sun, both behaviors may reduce phototoxicity associated with ingested plant materials. Furthermore, larvae ofC. chloroleucaria demonstrated a preference in the field for pollen, which constitutes a nonphototoxic tissue of their host plant. Experimental alterations of these specific behaviors induced important biological consequences for larvae of both insects such as mortality or reduction of larval growth rate. These results reinforce the idea that behavior may constitute an efficient adaptation to avoid phototoxicity.     

Transgenic carnations obtained byAgrobacterium tumefciens-mediated transformation of leaf explants

For the development of anAgrobacterium-mediated transformation procedure of carnation (Dianthus caryophyllus L.), an intron-containing -glucuronidase (gus) gene was used to monitor the frequency of transformation events soon after infection of leaf explants. The efficiency of gene transfer was dependent on the carnation genotype, explant age and cocultivation time. Leaf explants from the youngest leaves showed the highest number of GUS-positive spots. After selection on a kanamycin-containing medium, transgenic shoots were generated among a relatively high number of untransformed shoots. The selection procedure was modified in such a way that the contact between explant and medium was more intense. This improved the selection and decreased the number of escapes. Kanamycin-resistant and GUS-positive plants were obtained from five cultivars after infection of leaf explants with the supervirulentAgrobacterium strain AGLO. A higher transformation frequency was observed with the binary vector pCGN7001 than with the p35SGUSint vector. Integration of the genes into the carnation genome was demonstrated by Southern blot hybridization. The number of incorporated T-DNA insertions varied between independent transformants from one to eight. Transformants were morphologically identical to untransformed plants. Segregation of the genes occurred in a Mendelian way.     

The importance of naturally attenuated SARS-CoV-2in the fight against COVID-19

The current SARS-CoV-2 pandemic is wreaking havoc throughout the world and has rapidly become a global health emergency. A central question concerning COVID-19 is why some individuals become sick and others not. Many have pointed already at variation in risk factors between individuals. However, the variable outcome of SARS-CoV-2 infections may, at least in part, be due also to differences between the viral subspecies with which individuals are infected. A more pertinent question is how we are to overcome the current pandemic. A vaccine against SARS-CoV-2 would offer significant relief, although vaccine developers have warned that design, testing and production of vaccines may take a year if not longer. Vaccines are based on a handful of different designs (i), but the earliest vaccines were based on the live, attenuated virus. As has been the case for other viruses during earlier pandemics, SARS-CoV-2 will mutate and may naturally attenuate over time (ii). What makes the current pandemic unique is that, thanks to state-of-the-art nucleic acid sequencing technologies, we can follow in detail how SARS-CoV-2 evolves while it spreads. We argue that knowledge of naturally emerging attenuated SARS-CoV-2 variants across the globe should be of key interest in our fight against the pandemic.     

The evolutionary trade-offs in phage-resistant Klebsiella pneumoniae entail cross-phage sensitization and loss of multidrug resistance

Bacteriophage therapy is currently being evaluated as a critical complement to traditional antibiotic treatment. However, the emergence of phage resistance is perceived as a major hurdle to the sustainable implementation of this antimicrobial strategy. By combining comprehensive genomics and microbiological assessment, we show that the receptor-modification resistance to capsule-targeting phages involves either escape mutation(s) in the capsule biosynthesis cluster or qualitative changes in exopolysaccharides, converting clones to mucoid variants. These variants introduce cross-resistance to phages specific to the same receptor yet sensitize to phages utilizing alternative ones. The loss/modification of capsule, the main Klebsiella pneumoniae virulence factor, did not dramatically impact population fitness, nor the ability to protect bacteria against the innate immune response. Nevertheless, the introduction of phage drives bacteria to expel multidrug resistance clusters, as observed by the large deletion in K. pneumoniae 77 plasmid containing bla_CTX-M, ant(3″), sul2, folA, mph(E)/mph(G) genes. The emerging bacterial resistance to viral infection steers evolution towards desired population attributes and highlights the synergistic potential for combined antibiotic-phage therapy against K. pneumoniae.