Molecular characterization and expression analysis of selenoprotein W gene in rainbow trout (Oncorhynchus mykiss) with dietary selenium levels.

Selenium (Se) plays an essential role in the growth of fish and performs its physiological functions mainly through incorporation into selenoproteins. Our previous studies suggested that the selenoprotein W gene (selenow) is sensitive to changes in dietary Se in rainbow trout. However, the molecular characterization and tissue expression pattern of selenow are still unknown. Here, we revealed the molecular characterization, the tissue expression pattern of rainbow trout selenow and analyzed its response to dietary Se. The open reading frame (ORF) of the selenow gene was composed of 393 base pairs (bp) and encodes a 130-amino-acid protein. The 3' untranslated region (UTR) was 372 bp with a selenocysteine insertion sequence (SECIS) element. Remarkably, the rainbow trout selenow gene sequence was longer than those reported for mammals and most other fish. A ß1-α1-ß2-ß3-ß4-α2 pattern made up the secondary structure of SELENOW. Furthermore, multiple sequence alignment revealed that rainbow trout SELENOW showed a high level of identity with SELENOW from Salmo salar. In addition, the selenow gene was ubiquitously distributed in 13 tissues with various abundances and was predominantly expressed in muscle and brain. Interestingly, dietary Se significantly increased selenow mRNA expression in muscle. Our results highlight the vital role of selenow in rainbow trout muscle response to dietary Se levels and provide a theoretical basis for studies of selenow.

Phosphorus enrichment affects trait network topologies and the growth of submerged macrophytes.

Significant differences in the morphological and physiological characteristics of submerged macrophytes have been studied following nutrient addition, but little research has investigated the changes in plant trait network topology structures and trait interactions at the whole-plant perspective along nutrient gradients. Plant trait interactions and coordination strongly determine ecosystem structure and functioning. Thirty plant traits were collected from a three-month experiment to construct plant trait networks to clarify the variations in trait connections and network organization arising from five total phosphorus (TP) addition concentrations in water, including a control (CK), 0.1 (TP1), 0.2 (TP2), 0.4 (TP3), and 0.8 (TP4) mg L-1. Nonmetric multidimensional scaling analysis showed a clear difference in the distribution of plant trait space among the different TP treatments. Distinct network structures showed that water TP-deficiency and TP-repletion changed the plant trait network into loose assemblages of more modules, which was related to low plant carbohydrate levels. Most plant functions involving biomass accumulation and carbohydrate synthesis were reduced under high TP conditions compared to moderate TP enrichment. Moreover, the percentage of significant relationships between plant functions and corresponding network modules was lower in the CK and TP4 treatments. These results suggested that low plant carbohydrates in high TP environments induced by high water chlorophyll a and tissue phosphorus could not support rapid resource transport among organs and thus inefficiently performed plant functions. Plant carbohydrates were a vital variable that impacted the network edge density, trait interactions, and plant growth. In summary, we demonstrated that high water TP enrichment reduces plant trait network connectedness and plant functional potentials, which may be correlated with reducing tissue carbohydrates. This study explores the correlations between plant trait network topology and functions to improve our understanding of physiological and ecological rules regulating trait interactions among organs and plant growth under eutrophic conditions.

Stoichiometric and physiological mechanisms that link hub traits of submerged macrophytes with ecosystem structure and functioning.

Eutrophication strongly influences plant stoichiometric characteristics and physiological status by altering nutrient and light availability in the water column. However, the mechanisms linking plant functional traits with ecosystem structure and functioning to clarify the decline of submerged macrophytes have not been fully elucidated to date. Therefore, based on a field investigation of 26 macrophytic shallow lakes on the Yangtze Plain, we first constructed a plant trait network at the whole-plant level to determine the hub traits of submerged macrophytes that play central regulatory roles in plant phenotype. Our results suggested that organ (leaf, stem, and root) phosphorus (P), starch, and total nonstructural carbohydrate (TNC) contents were hub traits. Organ starch and TNC were consistent with those in the experiment-based network obtained from a three-month manipulation experiment. Next, the mechanisms underlying the relationships between the hub traits and vital aspects of ecological performance were carefully investigated using field investigation data. Specifically, stoichiometric homeostasis of P (HP), starch, and TNC were positively associated with dominance and biomass at the species level, and community biomass at the community level. Additionally, structural equation modeling clarified not only a hypothesized pathway from eutrophication to water clarity and community TNC, but also combined effects of community TNC and HP on community biomass. That is, ecosystems dominated by more homeostatic communities tended to have more carbon (C)-rich compounds in relatively oligotrophic conditions, which promoted the primary production of macrophytes. Eutrophication was determined to affect community structure by inhibiting the predominance of more homeostatic species and the production of carbohydrates. Finally, reduced community biomass and increased nutrient contents and nutrient:C ratios in plants induced by eutrophication implied a decrease in the C sink in biomass and may potentially lead to an enhancement of litter decomposition rates and nutrient cycling rates. By adjusting plant responses to eutrophication, stoichiometric and physiological mechanisms linking plant traits with ecosystem structure have important implications for understanding ecosystem processes, and these results may contribute to practical management to achieve the restoration of submerged macrophytes and ecosystem services.