Rapid loss of an ecosystem engineer: Sphagnum decline in an experimentally warmed bog

Sphagnum mosses are keystone components of peatland ecosystems. They facilitate the accumulation of carbon in peat deposits, but climate change is predicted to expose peatland ecosystem to sustained and unprecedented warming leading to a significant release of carbon to the atmosphere. Sphagnum responses to climate change, and their interaction with other components of the ecosystem, will determine the future trajectory of carbon fluxes in peatlands. We measured the growth and productivity of Sphagnum in an ombrotrophic bog in northern Minnesota, where ten 12.8‐m‐diameter plots were exposed to a range of whole‐ecosystem (air and soil) warming treatments (+0 to +9°C) in ambient or elevated (+500 ppm) CO₂. The experiment is unique in its spatial and temporal scale, a focus on response surface analysis encompassing the range of elevated temperature predicted to occur this century, and consideration of an effect of co‐occurring CO₂ altering the temperature response surface. In the second year of warming, dry matter increment of Sphagnum increased with modest warming to a maximum at 5°C above ambient and decreased with additional warming. Sphagnum cover declined from close to 100% of the ground area to <50% in the warmest enclosures. After three years of warming, annual Sphagnum productivity declined linearly with increasing temperature (13–29 g C/m² per °C warming) due to widespread desiccation and loss of Sphagnum. Productivity was less in elevated CO₂ enclosures, which we attribute to increased shading by shrubs. Sphagnum desiccation and growth responses were associated with the effects of warming on hydrology. The rapid decline of the Sphagnum community with sustained warming, which appears to be irreversible, can be expected to have many follow‐on consequences to the structure and function of this and similar ecosystems, with significant feedbacks to the global carbon cycle and climate change.     

Temporal constraints on the potential role of fry odors as cues of past reproductive success for spawning lake trout

Deciding where to reproduce is a major challenge for most animals. Many select habitats based upon cues of successful reproduction by conspecifics, such as the presence of offspring from past reproductive events. For example, some fishes select spawning habitat following odors released by juveniles whose rearing habitat overlaps with spawning habitat. However, juveniles may emigrate before adults begin to search for spawning habitat; hence, the efficacy of juvenile cues could be constrained by degradation or dissipation rates. In lake trout (Salvelinus namaycush), odors deposited by the previous year's offspring have been hypothesized to guide adults to spawning reefs. However, in most extant populations, lake trout fry emigrate from spawning reefs during the spring and adults spawn during the fall. Therefore, we postulated that the role of fry odors in guiding habitat selection might be constrained by the time between fry emigration and adult spawning. Time course chemical, physiological, and behavioral assays indicated that the odors deposited by fry likely degrade or dissipate before adults select spawning habitats. Furthermore, fry feces did not attract wild lake trout to constructed spawning reefs in Lake Huron. Taken together, our results indicate fry odors are unlikely to act as cues for lake trout searching for spawning reefs in populations whose juveniles emigrate before the spawning season, and underscore the importance of environmental constraints on social cues.     

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The Drosophila Baramicin polypeptide gene protects against fungal infection

The fruit fly Drosophila melanogaster combats microbial infection by producing a battery of effector peptides that are secreted into the haemolymph. Technical difficulties prevented the investigation of these short effector genes until the recent advent of the CRISPR/CAS era. As a consequence, many putative immune effectors remain to be formally described, and exactly how each of these effectors contribute to survival is not well characterized. Here we describe a novel Drosophila antifungal peptide gene that we name Baramicin A. We show that BaraA encodes a precursor protein cleaved into multiple peptides via furin cleavage sites. BaraA is strongly immune-induced in the fat body downstream of the Toll pathway, but also exhibits expression in other tissues. Importantly, we show that flies lacking BaraA are viable but susceptible to the entomopathogenic fungus Beauveria bassiana. Consistent with BaraA being directly antimicrobial, overexpression of BaraA promotes resistance to fungi and the IM10-like peptides produced by BaraA synergistically inhibit growth of fungi in vitro when combined with a membrane-disrupting antifungal. Surprisingly, BaraA mutant males but not females display an erect wing phenotype upon infection. Here, we characterize a new antifungal immune effector downstream of Toll signalling, and show it is a key contributor to the Drosophila antimicrobial response.     

cDNA cloning of phosphoethanolamine N-methyltransferase from spinach by complementation in Schizosaccharomyces pombe and characterization of the recombinant enzyme

The N-methylation of phosphoethanolamine is the committing step in choline biogenesis in plants and is catalyzed by S-adenosyl-L-methionine:phosphoethanolamine N-methyltransferase (PEAMT, EC ). A spinach PEAMT cDNA was isolated by functional complementation of a Schizosaccharomyces pombe cho2(-) mutant and was shown to encode a protein with PEAMT activity and without ethanolamine- or phosphatidylethanolamine N-methyltransferase activity. The PEAMT cDNA specifies a 494-residue polypeptide comprising two similar, tandem methyltransferase domains, implying that PEAMT arose by gene duplication and fusion. Data base searches suggested that PEAMTs with the same tandem structure are widespread among flowering plants. Size exclusion chromatography of the recombinant enzyme indicates that it exists as a monomer. PEAMT catalyzes not only the first N-methylation of phosphoethanolamine but also the two subsequent N-methylations, yielding phosphocholine. Monomethyl- and dimethylphosphoethanolamine are detected as reaction intermediates. A truncated PEAMT lacking the C-terminal methyltransferase domain catalyzes only the first methylation. Phosphocholine inhibits both the wild type and the truncated enzyme, although the latter is less sensitive. Salinization of spinach plants increases PEAMT mRNA abundance and enzyme activity in leaves by about 10-fold, consistent with the high demand in stressed plants for choline to support glycine betaine synthesis.     

Effect of growth conditions on isoprene emission and other thermotolerance‐enhancing compounds

Isoprene is emitted from the leaves of many plants in a light‐dependent and temperature‐sensitive manner. Plants lose a large fraction of photo‐assimilated carbon as isoprene but may benefit from improved recovery of photosynthesis following high‐temperature episodes. The capacity for isoprene emission of plants in natural conditions (assessed as the rate of isoprene emission under standard conditions) varies with weather. Temperature‐controlled greenhouses were used to study the role of temperature and light in influencing the capacity of oak leaves for isoprene synthesis. A comparison was made between the capacity for isoprene emission and the accumulation of other compounds suggested to increase thermotolerance of photosynthesis under two growth temperatures and two growth light intensities. It was found that the capacity for isoprene emission was increased by high temperature or high light. Xanthophyll cycle intermediates increased in high light, but not in high temperature, and the chloroplast small heat‐shock protein was not expressed in any of the growth conditions. Thus, of the three thermotolerance‐enhancing compounds studied, isoprene was the only one induced by the temperature used in this study.     

Precision and accuracy of Dahl-Lea back-calculated smolt lengths from adult scales of Atlantic salmon Salmo salar

Using tagged and recaptured Atlantic salmon Salmo salar (n = 106) the present analysis shows that the most commonly applied linear back-calculation method for estimating past length, the Dahl-Lea method, resulted in overestimation of the length of large smolts and underestimation of small smolts. A correction equation (y = 0.53x + 6.23) for estimating true smolt length (y) from lengths back-calculated from adult scale measures (x) to account for these systematic discrepancies is proposed.     

Light stimulation of proline synthesis in water-stressed barley leaves

The effect of light on [¹⁴C]glutamate conversion to free proline during water stress was studied in attached barley (Hordeum vulgare L.) leaves which had been trimmed to 10 cm in length. Plants at the three-leaf stage were stressed by flooding the rooting medium with polyethylene glycol 6000 (osmotic potential-19 bars) for up to 3 d. During this time the free proline content of 10-cm second leaves rose from about 0.02 to 2 mol/leaf while free glutamate content remained steady at about 0.6 mol/leaf. In stressed leaves, the amount of [¹⁴C]glutamate converted to proline in a 3-h period of light or darkness was taken to reflect the in-vivo rate of proline biosynthesis because the following conditions were met: (a) free-glutamate levels were not significantly different in light and darkness; (b) both tracer [¹⁴C]-glutamate and [¹⁴C]proline were rapidly absorbed; (c) rates of [¹⁴C]proline oxidation and incorporation into protein were very slow. As leaf water potential fell, more [¹⁴C]glutamate was converted to proline in both light and darkness, but at any given water potential in the range-12 to-20 bars, illuminated leaves converted twice as much [¹⁴C]glutamate to proline.     

The 5'-flanking region of the human CGL-1/granzyme B gene targets expression of a reporter gene to activated T-lymphocytes in transgenic mice.

The human CSP-B/CGL-1 gene is the homologue of the mouse granzyme B/CCPI gene and encodes a cytotoxic T-lymphocyte-specific serine protease. We have used regulatory sequences upstream from the CSP-B gene to drive human growth hormone gene expression in transgenic mice. Eleven founder mice were screened for transgene expression in activated T-cells. Expression was detected in 10 mice; levels of expression were integration site-dependent. The transgene was not expressed in resting lymphocytes but could be activated by treatment with concanavalin A or interleukin-2, indicating that CSP-B regulatory sequences are responsive to signals originating at either the T-cell receptor or the interleukin-2 receptor. Transgene expression was detected at the whole organ level only in lymph nodes and small intestine, where endogenous mouse CCPI mRNA was also present. The time course of transgene activation in T-lymphocytes was similar to that of the mouse CCPI gene. No differences in levels of expression of the transgene were observed in activated lymphocyte populations that had been depleted of either CD4+ or CD8+ cells; in contrast, the mouse CCPI gene was expressed primarily in CD8+ cells. Six CD4+ T-cell clones with Th0, Th1, or Th2 phenotypes were generated from a transgenic animal. All clones expressed moderate to high levels of the transgene, but only three clones expressed mouse CCPI, indicating that the transgene is disregulated in CD4+ T-cell subsets. The CSP-B regulatory unit represents a novel reagent for targeting gene expression to activated T-lymphocytes.