Two meiotic crossover classes cohabit in Arabidopsis: one is dependent on MER3,whereas the other one is not

BACKGROUND: Crossovers are essential for the completion of meiosis. Recently, two pathways of crossover formation have been identified on the basis of distinct genetic controls. In one pathway, crossover inhibits the occurrence of another such event in a distance-dependent manner. This phenomenon is known as interference. The second kind of crossover is insensitive to interference. The two pathways function independently in budding yeast. Only interference-insensitive crossovers occur in Schizosaccharomyces pombe. In contrast, only interference-sensitive crossovers occur in Caenorabditis elegans. The situation in mammals and plants remains unclear. Mer3 is one of the genes shown to be required for the formation of interference-sensitive crossovers in Saccharomyces cerevisiae. RESULTS: To unravel the crossover status in the plant Arabidopsis thaliana, we investigated the role of the A. thaliana MER3 gene through the characterization of a series of allelic mutants. All mer3 mutants showed low levels of fertility and a significant decrease (about 75%) but not a total disappearance of meiotic crossovers, with the number of recombination events initiated in the mutants being similar to that in the wild-type. Genetic analyses showed that the residual crossovers in mer3 mutants did not display interference in one set of adjacent intervals. CONCLUSIONS: Mutation in MER3 in Arabidopsis appeared to be specific to recombination events resulting in interference-sensitive crossovers. Thus, MER3 function is conserved from yeast to plants and may exist in other metazoans. Arabidopsis therefore has at least two pathways for crossover formation, one giving rise to interference-sensitive crossover and the other to independently distributed crossovers.     

Retinal degeneration progression changes lentiviral vector cell targeting in the retina

In normal mice, the lentiviral vector (LV) is very efficient to target the RPE cells, but transduces retinal neurons well only during development. In the present study, the tropism of LV has been investigated in the degenerating retina of mice, knowing that the retina structure changes during degeneration. We postulated that the viral transduction would be increased by the alteration of the outer limiting membrane (OLM). Two different LV pseudotypes were tested using the VSVG and the Mokola envelopes, as well as two animal models of retinal degeneration: light-damaged Balb-C and Rhodopsin knockout (Rho-/-) mice. After light damage, the OLM is altered and no significant increase of the number of transduced photoreceptors can be obtained with a LV-VSVG-Rhop-GFP vector. In the Rho-/- mice, an alteration of the OLM was also observed, but the possibility of transducing photoreceptors was decreased, probably by ongoing gliosis. The use of a ubiquitous promoter allows better photoreceptor transduction, suggesting that photoreceptor-specific promoter activity changes during late stages of photoreceptor degeneration. However, the number of targeted photoreceptors remains low. In contrast, LV pseudotyped with the Mokola envelope allows a wide dispersion of the vector into the retina (corresponding to the injection bleb) with preferential targeting of Müller cells, a situation which does not occur in the wild-type retina. Mokola-pseudotyped lentiviral vectors may serve to engineer these glial cells to deliver secreted therapeutic factors to a diseased area of the retina.     

Decomposers and root feeders interactively affect plant defence in <Emphasis Type="Italic">Sinapis alba</Emphasis>

Aboveground herbivory is well known to change plant growth and defence. In contrast, effects of soil organisms, acting alone or in concert, on allocation patterns are less well understood. We investigated separate and combined effects of the endogeic earthworm species Aporrectodea caliginosa and the root feeding nematode species Pratylenchus penetrans and Meloidogyne incognita on plant responses including growth and defence metabolite concentrations in leaves of white mustard, Sinapis alba. Soil biota had a strong impact on plant traits, with the intensity varying due to species combinations. Nematode infestation reduced shoot biomass and nitrogen concentration but only in the absence of earthworms. Earthworms likely counteracted the negative effects of nematodes. Infestation with the migratory lesion-nematode P. penetrans combined with earthworms led to increased root length. Earthworm biomass increased in the presence of this species, indicating that these nematodes increased the food resources of earthworms—presumably dead and decaying roots. Nitrogen-based defence compounds, i.e. glucosinolates, did not correlate with nitrogen levels. In the presence of earthworms, concentrations of aromatic glucosinolates in leaves were significantly increased. In contrast, infection with P. penetrans strongly decreased concentrations of glucosinolates (up to 81%). Infestation with the sedentary nematode M. incognita induced aromatic glucosinolates by more than 50% but only when earthworms were also present. Myrosinase activities, glucosinolate-hydrolysing enzymes, were unaffected by nematodes but reduced in the presence of earthworms. Our results document that root-feeding nematodes elicit systemic plant responses in defence metabolites, with the responses varying drastically with nematode species of different functional groups. Furthermore, systemic plant responses are also altered by decomposer animals, such as earthworms, challenging the assumption that induction of plant responses including defence traits is restricted to herbivores. Soil animals even interact and modulate the individual effects on plant growth and plant defence, thereby likely also influencing shoot herbivore attack.     

Competition for food between the exotic wasp <Emphasis Type="Italic">Vespula germanica</Emphasis> and the native ant assemblage of NW Patagonia: evidence of biotic resistance?

The success of a biological invasion may depend on the interactions between the invader and the native biota. However, little experimental evidence demonstrates whether local species can successfully compete with exotics. We experimentally determined the existence of competition for food between the exotic wasp Vespula germanica, one of the most recent Patagonian invaders, and the native ant assemblage. Both wasps and ants are generalist predators and scavengers, sharing habitat and food resources. We selected 30 sites within scrubland habitats where both ants and wasps were present. At each site, we placed containers with protein baits under three treatments: wasp exclusion, ant exclusion, and control (i.e., free access for wasps and ants). Ant exclusion increased the number of wasps (with regard to a control), but wasp exclusion did not affect ant abundance. This result suggests that native ants affect the foraging activity of exotic wasps but not vice versa. Aggressive behaviors and worker aggregation may explain the competitive advantage of ants. Ants bite wasp legs and massively aggregate on food sources, physically limiting the landing of wasps on baits. If the outcome of interactions at baits reported here influence wasp population-level parameters, this competitive interaction could be one of the factors explaining the low abundance of this exotic wasp in NW Patagonia in comparison with other invaded regions.     

Connections between climatic variables and the growth and needle dynamics of Scots pine (Pinus sylvestris L.) in Estonia and Lapland

The relationships between climatic variables and Scots pine (Pinus sylvestris L.) growth and needle dynamics were studied in three stands in Estonia and in four stands located near the northern timberline in Lapland. The trees sampled in Estonia had low correlations with the analysed climatic variables (air temperature, precipitation and indices of atmospheric circulation). Moreover, the weak cross-correlation of the time-series of the Estonian sample trees indicated that Scots pine is affected mainly by local factors in that region. In Lapland, however, height increment and needle production correlated strongly among trees within a stand (mean r=0.45 and 0.46, respectively) and between stands (r=0.32 and 0.37). Radial increment also showed a high inter-correlation among the trees within a stand in Lapland (r=0.45). Both height increment and needle production were strongly influenced by the temperature regime of the previous summer in Lapland (mean r=0.64 and 0.64, respectively). Radial increment was correlated with the mean July temperature of the current year (mean r=0.29). The correlations between the indices of atmospheric circulation and tree attributes were weak, while the strongest correlation was between the Ponta Delgada NAO index (PD–NAO) and height increment and needle production in Lapland. Height increment, needle production and radial increment have increased since the 1990s in the trees growing in Lapland. This may indicate a positive effect of climate warming on tree growth in Lapland. In Estonia, where climatic conditions do not limit tree growth, the climate warming seems not to directly influence the growth and needle dynamics of Scots pine.     

Field preferences of the Social Wasp Vespula germanica (Hymenoptera: Vespidae) for Protein-rich Baits

Food preferences displayed by foraging insects are important from a fundamental perspective and in pest control. We studied the preference of an invasive wasp, V. germanica, for protein foods in field conditions. Preferences were evaluated by placing baits in a paired design in different habitats and analyzing wasp visits, using a Bayesian approach to the Thurstone model. V. germanica workers display a clear rating of preferences, but were affected by the presence of competitors at the bait. These results contribute knowledge aimed at toxic baiting protocols for this wasp and suggest that food choice is a complex process subject to the influence of diverse factors. We emphasize the importance of on-site paired comparisons in preference studies to fully understand the drivers of food choice by insects.     

Somatic embryogenesis of the banana hybrid cultivar FHIA-18 (AAAB) in liquid medium and scaled-up in a bioreactor

The development of somatic embryos in liquid culture medium has a number of advantages for large-scale propagation of plants. This paper describes an improved system for the mass propagation via somatic embryogenesis of the banana hybrid cultivar FHIA-18 (AAAB). Explants from immature male flowers were used to form high frequency embryogenic tissue, this tissue was then used to establish embryogenic cell suspensions in a basic MS medium plus 1.0 mg l^–1 biotin, 100 mg l^–1 glutamine, 100 mg l^–1 malt extract (Sigma), 1.0 mg l^–1 2,4-D and 45 g l^–1 sucrose. Secondary multiplication of somatic embryos was achieved in liquid media in rotary shaker and in bioreactors. The number of embryos per litre obtained with 80.0% DO₂ and effects of pH were also studied. A high regeneration percentage of plants were obtained (89.3%) in only 1 month of culture, somatic embryos were then placed to germinate in temporary immersion systems and field testing of somaclonal variation.     

Transient Transfection of a Wild-Type p53 Gene Triggers Resveratrol-Induced Apoptosis in Cancer Cells

Resveratrol is a promising chemopreventive agent that mediates many cellular targets involved in cancer signaling pathways. p53 has been suggested to play a role in the anticancer properties of resveratrol. We investigated resveratrol-induced cytotoxicity in H1299 cells, which are non-small lung cancer cells that have a partial deletion of the gene that encodes the p53 protein. The results for H1299 cells were compared with those for three cell lines that constitutively express wild-type p53: breast cancer MCF-7, adenocarcinomic alveolar basal epithelia A549 and non-small lung cancer H460. Cell viability assays revealed that resveratrol reduced the viability of all four of these cell lines in a dose- and time-dependent manner. MCF-7, A549 and H460 cells were more sensitive to resveratrol than were H1299 cells when exposed to the drug for 24 h at concentrations above 100 µM. Resveratrol also increased the p53 protein levels in MCF-7 cells without altering the p53 mRNA levels, suggesting a post-translational modulation of the protein. The resveratrol-induced cytotoxicity in these cells was partially mediated by p53 and involved the activation of caspases 9 and 7 and the cleavage of PARP. In H1299 cells, resveratrol-induced cytotoxicity was less pronounced and (in contrast to MCF-7 cells) cell death was not accompanied by caspase activation. These findings are consistent with the observation that MCF-7 cells were positively labeled by TUNEL following exposure to 100 µM resveratrol whereas H1299 cells under similar conditions were not labeled by TUNEL. The transient transfection of a wild-type p53-GFP gene caused H1299 cells to become more responsive to the pro-apoptotic properties of resveratrol, similarly to findings in the p53-positive MCF-7 cells. Our results suggest a possible therapeutic strategy based on the use of resveratrol for the treatment of tumors that are typically unresponsive to conventional therapies because of the loss of normal p53 function.     

Mate‐searching behavior in the invasive German wasp,Vespula germanica,in Patagonia

In order to increase the probability of reproduction, social insects can adopt various mate‐finding strategies, such as increasing densities of males at specific locations, and/or visual and chemical cues that attract the opposite sex. In field and laboratory studies we investigated strategies used by the invasive eusocial wasp Vespula germanica (Fabricius) (Hymenoptera: Vespidae). In tethered flight assays, we established contrasting flight patterns in females and males that may partly explain how related individuals distribute spatially during the mating period. We also determined experimentally, in the field and in the laboratory via olfactometer assays, that gynes produce airborne pheromonal cues that attract drones and are important during mate location. Our field trials also suggest that visual cues play a role in mate location. We conclude that in addition to aspects of the social biology of the species, an efficient mate‐location strategy can partly explain the invasion success of the species. Tools to mitigate the damage caused by yellowjackets may be developed by focusing on reproductive castes, in addition to workers.