Structural properties of the peroxiredoxin AhpC2 from the hyperthermophilic eubacterium Aquifex aeolicus

Peroxiredoxins (Prxs) are thiol peroxidases that scavenge various peroxide substrates such as hydrogen peroxide (H₂O₂), alkyl hydroperoxides and peroxinitrite. They also function as chaperones and are involved in signal transduction by H₂O₂ in eukaryotic cells. The genome of Aquifex aeolicus, a microaerophilic, hyperthermophilic eubacterium, encodes four Prxs, among them an alkyl hydroperoxide reductase AhpC2 which was found to be closely related to archaeal 1-Cys peroxiredoxins. We determined the crystal structure of AhpC2 at 1.8?Å resolution and investigated its oligomeric state in solution by electron microscopy. AhpC2 is arranged as a toroid-shaped dodecamer instead of the typically observed decamer. The basic folding topology and the active site structure are conserved and possess a high structural similarity to other 1-Cys Prxs. However, the C-terminal region adopts an opposite orientation. AhpC2 contains three cysteines, Cys⁴⁹, Cys²¹², and Cys²¹⁸. The peroxidatic cysteine C_P⁴⁹ was found to be hyperoxidized to the sulfonic acid (SO₃H) form, while Cys²¹² forms an intra-monomer disulfide bond with Cys²¹⁸. Mutagenesis experiments indicate that Cys²¹² and Cys²¹⁸ play important roles in the oligomerization of AhpC2. Based on these structural characteristics, we proposed the catalytic mechanism of AhpC2. This study provides novel insights into the structure and reaction mechanism of 1-Cys peroxiredoxins.     

Anatomical and phenological implications of the relationship between Schinus polygama (Cav.) (Cabrera) and the galling insect Calophya rubra (Blanchard)

• The success of galling insects could be determined by synchronisation with host plant phenology and climate conditions, ensuring suitable oviposition sites for gall induction and food resources for their survival. The anatomical, histochemical and phenological synchronisation strategies between Calophya rubra (Blanchard) (Hemiptera: Psylloidea) and its host, the evergreen plant Schinus polygama (Cav.) (Cabrera) (Anacardiaceae), in the Mediterranean climate of southern Chile was evaluated and compared to that of the congeneric C. cf. duvauae (Scott) from Brazil and closely related host plant S. engleri in a subtropical climate.
• Anatomical, histometric, histochemical and vegetative phenology studies of the stem and galls were conducted from June 2015 to December 2016.
• Based on the anatomical, histometric and histochemical analysis, the conical stem gall traits imply gains over the non‐galled stem toward the galling insect survival, but the maintenance of phellem, secretory ducts and pith indicate conservative developmental traits that cannot be manipulated by C. rubra. Our results indicate that the conditions of the Mediterranean climate zone limit C. rubra immature activity during unfavourable periods, probably determining a diapause period and a univoltine life cycle, which are peculiarities of the S. polygama– C. rubra system.
• The synchronisation between development and seasonality confers peculiarities to the S. polygama– C. rubra system in the Mediterranean climate zone.

     

Are species photosynthetic characteristics good predictors of seedling post-hurricane demographic patterns and species spatiotemporal distribution in a hurricane impacted wet montane forest?

In situ measurements of leaf level photosynthetic response to light were collected from seedlings of ten tree species from a tropical montane wet forest, the John Crow Mountains, Jamaica. A model-based recursive partitioning ('mob') algorithm was then used to identify species associations based on their fitted photosynthetic response curves. Leaf area dark respiration (R_D) and light saturated maximum photosynthetic (A_max) rates were also used as 'mob' partitioning variables, to identify species associations based on seedling demographic patterns (from June 2007 to May 2010) following a hurricane (Aug. 2007) and the spatiotemporal distribution patterns of stems in 2006 and 2012. R_D and A_max rates ranged from 1.14 to 2.02 μmol (CO₂) m⁻²s⁻¹ and 2.97–5.87 μmol (CO₂) m⁻²s⁻¹, respectively, placing the ten species in the range of intermediate shade tolerance. Several parsimonious species 'mob' groups were formed based on 1) interspecific differences among species response curves, 2) variations in post-hurricane seedling demographic trends and 3) R_D rates and species spatiotemporal distribution patterns at aspects that are more or less exposed to hurricanes. The composition of parsimonious groupings based on photosynthetic curves was not concordant with the groups based on demographic trends but was partially concordant with the R_D - species spatiotemporal distribution groups. Our results indicated that the influence of photosynthetic characteristics on demographic traits and species distributions was not straightforward. Rather, there was a complex pattern of interaction between ecophysiological and demographic traits, which determined species successional status, post-hurricane response and ultimately, species distribution at our study site.     

Tree seedling response to LED spectra: implications for forest restoration

We found that different spectra, provided by light-emitting diodes or a fluorescent lamp, caused different photomorphological responses depending on tree seedling type (coniferous or broad-leaved), species, seedling development stage, and seedling fraction (shoot or root). For two conifers (Picea abies and Pinus sylvestris) soon after germination (≤40 days), more seedling growth was related to a lower ratio of red-to-far-red (R:FR) light. As growth continued to 120 days, spectra with a greater complement of blue light yielded more growth. Roots showed more plasticity to light spectra than shoots. In general for the evergreen broad-leaved Quercus ilex, spectra with additional R:FR than for conifers yielded more growth in the first 57 days. Subsequently as seedlings grew, shoot growth appeared to be influenced less by light source than roots, with root length showing the greatest responses. Our results suggest that manipulating light spectra to foster desired seedling traits may be another tool for use in the production of high-quality seedlings as defined through the Target Plant Concept. Such seedlings are needed for restoration of the two billion hectares of degraded forestland, especially on harsh sites such as those found in the Mediterranean region, and to sequester carbon to mitigate climate change.     

Description of a new species and redescription of two species of the genus Limoniscus Reitter (Coleoptera,Elateridae, Dendrometrinae) from Japan

We presented a revised taxonomy of two allied species, Limoniscus mitokiiKishii, 2004 and L. ogatai (Kishii, 1985), from western Japan. Through this revision, we found a new species, L. spelunca sp. n., from the type series of L. ogatai. The new species is different in its frons, antennae, prosternum, and aedeagus compared with L. mitokii and L. ogatai. We also reviewed the current understanding of Japanese Limoniscus species, and provided a key to the 23 Limoniscus species found in Japan. urn:lsid:zoobank.org:pub:56104650-EAA9-42E9-AFC3-91D7DCA53938.     

Generalism in the interaction of Tulasnellaceae mycobionts with orchids characterizes a biodiversity hotspot in the tropical Andes of Southern Ecuador

Biotic interactions play an important role in the assembly and stability of communities. All orchids depend on mycobionts for early establishment, but whether individual orchid species depend on a specific or broad spectrum of mycobionts is still a matter of debate. Tulasnellaceae (Basidiomycota) is the richest and most widespread mycobiont worldwide. We assessed Tulasnellaceae richness in epiphytic and terrestrial orchids in different habitats, and evaluated the degree of generalism in orchid-Tulasnellaceae interactions and the robustness of this mutualistic system to the extinction of mycobiont partners. We sampled 114 orchid individuals including all common and rare species in 56 plots of 1 m² in 3 habitats: pristine forest, regenerating forest and a landslide site in a tropical montane rainforest in Southern Ecuador. We found 52 orchid and 29 Tulasnellaceae species. The composition of Tulasnellaceae OTUs was moderately to highly similar across habitats and between orchid growth forms. A significantly nested network architecture indicated the existence of a core of generalist Tulasnellaceae OTUs interacting with both rare and common orchids. Terrestrial and epiphytic orchids showed significant differences in robustness to the extinction of their Tulasnellaceae mycobionts. Thus, generalist mycobionts may be relevant for the preservation of hyperdiverse orchid communities in the tropics.