Puumala hantavirus infection alters the odour attractiveness of its reservoir host

The random-mixing assumptions of many parasite-transmission models are challenged if healthy individuals can alter their behaviour to reduce their risk of infection. Some pathogens reduce the attractiveness of their hosts’ excretions, for example, potentially altering contact rates and thus the predicted force of infection for pathogens transmissible by contact with excretions. For bank voles (Myodes glareolus), contact with contaminated urine is an important route of transmission for Puumala hantavirus (PUUV); however, it is not known whether PUUV infection changes the voles’ urinary odours or their attractiveness. Here, we use a Y-maze to test whether PUUV infection alters the attractiveness of male bank voles’ urine. We presented wild-caught PUUV-free male and female bank voles with PUUV-infected conspecific urine, uninfected urine and a water control, and measured the relative and absolute latency to first visit, number of visits, and total time bank voles spent investigating each treatment over 30 min. PUUV infection significantly altered the bank voles’ initial response to conspecific urine, with fewer visits and less time spent close to infected urine relative to uninfected urine, and less total time spent near the infected urine than the uninfected urine or control. These strong preferences weakened over the 30-min trial, however, partly due to a general decline in male activity, and there were no absolute differences between the treatments overall. This suggests that PUUV infection does change the attractiveness of bank vole urine to conspecifics, and we discuss the implications of these results for random-mixing assumptions.     

Volatiles emitted from in vitro grown tomato shoots during abiotic and biotic stress

Different stress factors were applied to in vitro grown tomato shoots (Lycopersicon esculentum Mill. `Moneymaker') to investigate the volatiles released in the headspace. Solid phase microextraction was used for the experiments with an abiotic stress factor (constant light) and automated dynamic sampling was used for the experiments with a biotic stress factor (Spodoptera littoralis caterpillar). Continuous light as stress factor induced constant emission of the sesquiterpene a-copaene. Constant emission was not found with any other sesquiterpene or with monoterpenes. Therefore, we hypothesize that this compound needs light for its biosynthesis and/ or emission. An attack by caterpillars caused an immediate higher emission of the constitutive compounds (mono-and sesquiterpenes) and the induced compounds (linalool and indole); the latter were emitted approximately 1 day after the attack and linalool was even emitted 2 days after removal of the caterpillar.     

Conservation measures for <Emphasis Type="Italic">Rosa arvensis</Emphasis> Huds. in Flanders (Belgium) based on congruent genetic and phenotypic population differentiation

Rosa arvensis is a naturally rare and scattered indigenous wild rose species in Flanders, the northern part of Belgium. As is the case for many light demanding woody species in this area, it is currently threatened by habitat fragmentation and destruction due to high human pressure. Recent inventories revealed a restricted distribution pattern for this rose, concentrated mainly in two regions of the south western part of Flanders. Surprisingly, strong differentiation was observed among natural populations in these two proximate regions in both an AFLP-based and a morphological analysis. A common garden experiment indicated a partly genetic basis for the morphological divergence. Additionally, the AFLP analysis of roses sampled in the same forested area within one of the two regions resulted in two differentiated gene pools. Possible causes for the observed differentiation can be adaptive divergence, founder effects and/or historical hybridisation with dogroses. Together, the congruent genetic and morphometric differentiation between the two geographic regions urges a cautious approach in conservation programs.     

Synergistic Degradation of Linuron by a Bacterial Consortium and Isolation of a Single Linuron-Degrading Variovorax Strain

The bacterial community composition of a linuron-degrading enrichment culture and the role of the individual strains in linuron degradation have been determined by a combination of methods, such as denaturing gradient gel electrophoresis of the total 16S rRNA gene pool, isolation and identification of strains, and biodegradation assays. Three strains, Variovorax sp. strain WDL1, Delftia acidovorans WDL34, and Pseudomonas sp. strain WDL5, were isolated directly from the linuron-degrading culture. In addition, subculture of this enrichment culture on potential intermediates in the degradation pathway of linuron (i.e., N,O-dimethylhydroxylamine and 3-chloroaniline) resulted in the isolation of, respectively, Hyphomicrobium sulfonivorans WDL6 and Comamonas testosteroni WDL7. Of these five strains, only Variovorax sp. strain WDL1 was able to use linuron as the sole source of C, N, and energy. WDL1 first converted linuron to 3,4-dichloroaniline (3,4-DCA), which transiently accumulated in the medium but was subsequently degraded. To the best of our knowledge, this is the first report of a strain that degrades linuron further than the aromatic intermediates. Interestingly, the rate of linuron degradation by strain WDL1 was lower than that for the consortium, but was clearly increased when WDL1 was coinoculated with each of the other four strains. D. acidovorans WDL34 and C. testosteroni WDL7 were found to be responsible for degradation of the intermediate 3,4-DCA, and H. sulfonivorans WDL6 was the only strain able to degrade N,O-dimethylhydroxylamine. The role of Pseudomonas sp. strain WDL5 needs to be further elucidated. The degradation of linuron can thus be performed by a single isolate, Variovorax sp. strain WDL1, but is stimulated by a synergistic interaction with the other strains isolated from the same linuron-degrading culture.     

Urbanization drives community shifts towards thermophilic and dispersive species at local and landscape scales

The increasing conversion of agricultural and natural areas to human‐dominated urban landscapes is predicted to lead to a major decline in biodiversity worldwide. Two conditions that typically differ between urban environments and the surrounding landscape are increased temperature, and high patch isolation and habitat turnover rates. However, the extent and spatial scale at which these altered conditions shape biotic communities through selection and/or filtering on species traits are currently poorly understood. We sampled carabid beetles at 81 sites in Belgium using a hierarchically nested sampling design wherein three local‐scale (200 × 200 m) urbanization levels were repeatedly sampled across three landscape‐scale (3 × 3 km) urbanization levels. First, we showed that communities sampled in the most urbanized locations and landscapes displayed a distinct species composition at both local and landscape scale. Second, we related community means of species‐specific thermal preferences and dispersal capacity (based on European distribution and wing morphology, respectively) to the urbanization gradients. We showed that urban communities consisted on average of species with a preference for higher temperatures and with better dispersal capacities compared to rural communities. These shifts were caused by an increased number of species tolerating higher temperatures, a decreased richness of species with low thermal preference, and an almost complete depletion of species with very low‐dispersal capacity in the most urbanized localities. Effects of urbanization were most clearly detected at the local scale, although more subtle effects could also be found at the scale of entire landscapes. Our results demonstrate that urbanization may fundamentally and consistently alter species composition by exerting a strong filtering effect on species dispersal characteristics and favouring replacement by warm‐dwelling species.     

Cellular co-factors of HIV-1 integration

To achieve productive infection, the reverse transcribed cDNA of human immunodeficiency virus type 1 (HIV-1) is inserted in the host cell genome. The main protein responsible for this reaction is the viral integrase. However, studies indicate that the virus is assisted by cellular proteins, or co-factors, to achieve integration into the infected cell. The barrier-to-autointegration factor (BAF) might prevent autointegration. Its ability to bridge DNA and the finding that the nuclear lamina-associated polypeptide-2alpha interacts with BAF suggest a role in nuclear structure organization. Integrase interactor 1 was found to directly interact with HIV-1 integrase and to activate its DNA-joining activity, and the high mobility group chromosomal protein A1 might approximate both long terminal repeat (LTR) ends and facilitate integrase binding by unwinding the LTR termini. Furthermore, the lens-epithelium-derived growth factor (LEDGF; also known as p75) seems to tether HIV-1 integrase to the chromosomes. Although a direct role in integration has only been demonstrated for LEDGF/p75, to date, each validated cellular co-factor for HIV-1 integration could constitute a promising new target for antiviral therapy.     

The Halophyte Seashore Paspalum Uses Adaxial Leaf Papillae for Sodium Sequestration

Salinity is a growing issue worldwide, with nearly 30% of arable land predicted to be lost due to soil salinity in the next 30 years. Many grass crops that are vital to sustain the world’s caloric intake are salt sensitive. Studying mechanisms of salt tolerance in halophytic grasses, plants that thrive in salt conditions, may be an effective approach to ultimately improve salt-sensitive grass crops. Seashore paspalum (Paspalum vaginatum) is a halophytic Panicoid grass able to grow in salt concentrations near that of seawater. Despite its widespread cultivation as a sustainable turfgrass, the mechanism underlying its ability to retain high Na⁺ concentrations in photosynthetic tissue while maintaining growth remains unknown. We examined the leaf structure and ion content in P. vaginatum ‘HI10’, which shows increased growth under saline conditions, and Paspalum distichum ‘Spence’, which shows reduced growth under salt, to better understand the superior salt tolerance of cv HI10. A striking difference between cv HI10 and cv Spence was the high steady-state level of K⁺ in cv HI10. Imaging further showed that the adaxial surface of both cv HI10 and cv Spence contained dense costal ridges of papillae. However, these unicellular extensions of the epidermis were significantly larger in cv HI10 than in cv Spence. The cv HI10 papillae were shown to act as Na⁺ sinks when plants were grown under saline conditions. We provide evidence that leaf papillae function as specialized structures for Na⁺ sequestration in P. vaginatum, illustrating a possible path for biotechnological improvement of salt-sensitive Panicoid crops with analogous leaf structures.

About 20% of irrigated land is considered saline, with the amount of saline soils increasing worldwide (Mayak et al., 2004). This is due to increased irrigation in agricultural fields necessitated by more frequent droughts due to climate change. This trend is alarming due to the high salt sensitivity of most crop species that we rely on for vital resources. Yield reduction in crops in saline soils amounts to losses on the order of 12 to 27.3 billion U.S. dollars annually (Qadir et al., 2014). Thus, the improvement of salt tolerance in plants will become key in the coming decades. Breeding salt-tolerant crops is a cost-effective approach to improve growth in saline soils. Although much work has focused on breeding salt-tolerant species, progress in this area has been slow due to the complex genetic and physiological nature of the salt response. Furthermore, most research has been conducted on glycophytic model systems that are salt sensitive (Munns and Gilliham, 2015). Unraveling the salt-tolerance mechanisms in halophytes, species that can complete their life cycle in 200 mm salt concentrations, and transferring these pathways into glycophytes is therefore of great interest (Rajalakshmi and Parida, 2012; Roy and Chakraborty, 2014).Both glycophytes and halophytes have evolved a multitude of salt-tolerance mechanisms, including sodium (Na⁺) exclusion, sequestration, and secretion; osmolyte production; ion homeostasis; and reactive oxygen species (ROS) detoxification (Meng et al., 2018). Often, mechanisms present in glycophytes, such as osmolyte production and Na⁺ exclusion, are utilized in halophytes at higher efficiency (Wyn Jones and Storey, 1981; Grieve and Maas, 1984). However, halophytes also use mechanisms that are absent in glycophytes. Salt sequestration and secretion via salt glands is a halophyte-specific mechanism of coping with salt (Flowers and Colmer, 2008). Salt glands are found in over 50 species in 14 angiosperm families with four subtypes: epidermal bladder cells, complex multicellular glands, bicellular glands, and unicellular glands (Dassanayake and Larkin, 2017). The Poales order contains ∼8% of all halophytes (Flowers et al., 2010) and has therefore been the focus of much salt-gland-focused work (Ceccoli et al., 2015). As salt tolerance has independently evolved >70 times in grass lineages (Bennett et al., 2013), studying these salt sequestering/secreting structures in grasses is an excellent approach to better understand salt tolerance mechanisms in halophytes.Most structural and physiological work on salt glands in grasses has been conducted in the Chloridoideae and Oryzoideae subfamilies. Grasses carry either unicellular or bicellular glands, often referred to as glandular trichomes or microhairs, on the leaf surface (Dassanayake and Larkin, 2017). Microhairs have been observed on the leaf surface in all grass subfamilies except the Pooideae, and have evolved diverse functions including the sequestration or secretion of substances such as callose and heavy metals (Burke et al., 2000; Ceccoli et al., 2015). Unicellular structures on the adaxial leaf side able to secrete salt are only found in the Oryzoideae wild rice species Porteresia coarctata (Flowers et al., 1990; Sengupta and Majumder, 2009). Salt glands in the Chloridoideae are bicellular, consisting of a cap cell and a lower basal cell, both of which are dense in cytoplasm and mitochondria (Ceccoli et al., 2015). The cuticle is thickened above the cap cell in some species, forming a cuticular chamber used for storing secreted salts (Amarasinghe and Watson, 1988). In the Panicoideae, a few cases of Na⁺ secretion have been reported (McWhorter et al., 1995; Ramadan and Flowers, 2004), but to date, no sequestration structures have been identified.The Panicoideae subfamily includes the agronomically important food crops maize (Zea mays) and sorghum (Sorghum bicolor) in addition to the biofuel grasses miscanthus (Miscanthus sinensis), switchgrass (Panicum virgatum), and sugarcane (Saccharum officinarum). One of the most salt-tolerant species in the Panicoideae is the halophyte seashore paspalum (Paspalum vaginatum). It is cultivated as a turfgrass worldwide and derives its popularity from its ability to be irrigated with brackish water. P. vaginatum can survive in salt concentrations near that of seawater (Uddin et al., 2012) and uses osmolyte production, ion homeostasis, and Na⁺ exclusion to cope with salt stress (Peacock and Dudeck, 1985; Lee et al., 2008; Guo et al., 2016). However, its ability to maintain growth while accumulating high levels of Na⁺ in leaf tissue remains perplexing.Here, we studied the leaf structure and Na⁺ sequestration in ‘HI10’, a P. vaginatum cultivar, and ‘Spence’, a Paspalum distichum cultivar. P. vaginatum and P. distichum are closely related (and possibly the same species; Eudy et al., 2017), and constitute group “Disticha” in the tribe Paspaleae. P. distichum is less salt tolerant than P. vaginatum and is typically found in freshwater habitats (Leithead et al., 1971). P. vaginatum and P. distichum therefore represent a useful species pair to study salt tolerance. Furthermore, their salt responses can be compared with those of sorghum, a Panicoid glycophyte. Our main research objective was to identify the phenotypic and physiological factors that contribute to the differential tolerance to salt stress of the two Paspalum spp. cultivars and sorghum ‘BTx623’. We show that both Paspalum species contain dense rows of translucent papillae on the adaxial surface. The papillae are unicellular protrusions from epidermal cells and are much larger in cv HI10 than in cv Spence. We further demonstrate that the papillae sequester Na⁺ under salt stress. This study thus provides evidence of Na⁺ sequestration in specialized leaf-borne organs within the Panicoideae.