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LRRC8 family proteins on the plasma membrane play a critical role in cellular osmoregulation by forming volume-regulated anion channels (VRACs) necessary to prevent necrotic cell death.We demonstrate that intracellular LRRC8 proteins acting within lysosomes also play an essential role in cellular osmoregulation. LRRC8 proteins on lysosome membranes generate large lysosomal volume-regulated anion channel (Lyso-VRAC) currents in response to low cytoplasmic ionic strength conditions. When a double-leucine L706L707 motif at the C terminus of LRRC8A was mutated to alanines, normal plasma membrane VRAC currents were still observed, but Lyso-VRAC currents were absent. We used this targeting mutant, as well as pharmacological tools, to demonstrate that Lyso-VRAC currents are necessary for the formation of large lysosome-derived vacuoles, which store and then expel excess water to maintain cytosolic water homeostasis. Thus, Lyso-VRACs allow lysosomes of mammalian cells to act as the cells “bladder.” When Lyso-VRAC current was selectively eliminated, the extent of necrotic cell death to sustained stress was greatly increased, not only in response to hypoosmotic stress, but also to hypoxic and hypothermic stresses. Thus Lyso-VRACs play an essential role in enabling cells to mount successful homeostatic responses to multiple stressors.

\"Animal Osmoregulation has three main themes. The first deals with the physical properties of water, its interaction with solutes and biological molecules, and the influence that these interactions have on the most fundamental aspects of biological design. The second involves the influence of the environment on an organism's physiology. Thirdly, while each environment dictates certain requirements that animals must fulfil, the evolutionary history of the animal strongly influences the physiological solution employed.\" \"The topic is addressed using examples from throughout the animal kingdom. This accessible supplementary text is suitable for both senior undergraduate and graduate students taking courses in comparative animal physiology and environmental physiology. It will also appeal to the many researchers requiring a concise but authoritative overview of the topic.\"--BOOK JACKET.

Osmoregulation and osmoconformation are two mechanisms through which aquatic animals adapt to salinity fluctuations. The euryhaline crab Scylla paramamosain, being both an osmoconformer and osmoregulator, is an excellent model organism to investigate salinity adaptation mechanisms in brachyurans. In the present study, we used transcriptomic and proteomic approaches to investigate the response of S. paramamosain to salinity stress. Crabs were transferred from a salinity of 25 ppt to salinities of 5 ppt or 33 ppt for 6 h and 10 days. Data from both approaches revealed that exposure to 5 ppt resulted in upregulation of ion transport and energy metabolism associated genes. Notably, acclimation to low salinity was associated with early changes in gene expression for signal transduction and stress response. In contrast, exposure to 33 ppt resulted in upregulation of genes related to amino acid metabolism, and amino acid transport genes were upregulated only at the early stage of acclimation to this salinity. Our study reveals contrasting mechanisms underlying osmoregulation and osmoconformation within the salinity range of 5–33 ppt in the mud crab, and provides novel candidate genes for osmotic signal transduction, thereby providing insights on understanding the salinity adaptation mechanisms of brachyuran crabs.

Whole-genome sequencing of the seagrass Zostera , representing the first marine angiosperm genome to be fully sequenced, provides insight into the evolutionary changes associated with a transition to a marine environment in this angiosperm lineage. The genome of the seagrass Zostera marina The seagrass Zostera marina , or eelgrass, is widely distributed throughout the Northern Hemisphere. It is therefore of considerable ecological importance but — as with other seagrasses — its coastal habitats are among the world's most threatened ecosystems. Jeanine Olsen and colleagues report the whole-genome sequence of Zostera . Their analyses provide insights into the evolutionary changes associated with the 'back to the sea' reverse evolutionary trajectory that has occurred in this angiosperm lineage, including the loss of the entire repertoire of stomatal genes, and the presence of sulfated cell-wall polysaccharides that are more macro-algal-like than plant-like. Seagrasses colonized the sea 1 on at least three independent occasions to form the basis of one of the most productive and widespread coastal ecosystems on the planet 2 . Here we report the genome of Zostera marina (L.), the first, to our knowledge, marine angiosperm to be fully sequenced. This reveals unique insights into the genomic losses and gains involved in achieving the structural and physiological adaptations required for its marine lifestyle, arguably the most severe habitat shift ever accomplished by flowering plants. Key angiosperm innovations that were lost include the entire repertoire of stomatal genes 3 , genes involved in the synthesis of terpenoids and ethylene signalling, and genes for ultraviolet protection and phytochromes for far-red sensing. Seagrasses have also regained functions enabling them to adjust to full salinity. Their cell walls contain all of the polysaccharides typical of land plants, but also contain polyanionic, low-methylated pectins and sulfated galactans, a feature shared with the cell walls of all macroalgae 4 and that is important for ion homoeostasis, nutrient uptake and O 2 /CO 2 exchange through leaf epidermal cells. The Z. marina genome resource will markedly advance a wide range of functional ecological studies from adaptation of marine ecosystems under climate warming 5 , 6 , to unravelling the mechanisms of osmoregulation under high salinities that may further inform our understanding of the evolution of salt tolerance in crop plants 7 .

The salinity of many freshwaters is increasing globally as a result of human activities. Associated with this increase in salinity are losses of Ephemeroptera (mayfly) abundance and richness. The salinity concentrations at which Ephemeroptera decline in nature are lower than their internal salinity or haemolymph osmolality. Many species also suffer substantial mortality in single species laboratory toxicity tests at salinities lower than their internal salinity. These findings are problematic as conventional osmoregulation theory suggests that freshwater animals should not experience stress where external osmolality is greater than haemolymph osmolality. Here I explore three hypotheses to explain salt sensitivity in Ephemeroptera. These conceptual hypotheses are based on the observations that as the external sodium ion (Na + ) concentration increases so does the Na + turnover rate (both uptake and elimination rates increase). Sulphate ( ) uptake in mayflies also increases with increasing external although, unlike Na + , its rate of increase decreases with increasing external . The first hypothesis is premised on ion turnover being energetically costly. The first hypothesis proposes that individuals must devote a greater proportion of their energy to ion homeostasis at the expense of other uses including growth and development. Lethal levels of salinity presumably result from individuals not being able to devote enough energy to maintain ion homeostasis without critical loss of other vital functions. The second hypothesis is premised on the uptake of Na + exchanged for (an outgoing) H + , leading to (localized) loss of pH regulation. The third hypothesis is premised on localized Na + toxicity or poisoning with increased Na turnover as salinity increases. None of the proposed hypotheses is without potential problems, yet all are testable, and research effort should be focused at attempting to falsify them. This article is part of the theme issue ‘Salt in freshwaters: causes, ecological consequences and future prospects’.

Naked carp ( Gymnocypris przewalskii ), endemic to the saline-alkaline Lake Qinghai, have the capacity to tolerate combinations of high salinity and alkalinity, but migrate to spawn in freshwater rivers each year. In this study, we measured the drinking rate over a 24 h period for naked carp exposed to saline-alkaline lake waters with salinities of 15 (L15) and 17 (L17). We also assessed the daily feed intakes of naked carp exposed to L15 and fresh water (FW). Additionally, we studied the daily expression of acid–base regulation and osmoregulation related genes and proteins in the intestine of naked carp exposed to saline-alkaline lake waters. Our results revealed that the drinking rate at night was significantly higher than in daytime when exposed to either L15 or L17, while feed intakes in daytime were significantly higher than at night. The relative expression of Na + /K + -ATPase α (NKA-α), solute carrier family members 26A6 (SLC26A6) and 4A4 (SLC4A4) in the intestine of naked carp exposed to L17 at night was higher than in daytime. Specifically, NKA-α mRNA expression at 4:00 was 7.22-fold and 5.63-fold higher than that at 10:00 and 16:00, respectively, and the expression at 22:00 was 11.29-fold and 8.80-fold higher than that at 10:00 and 16:00, respectively. Similarly, SLC26A6 mRNA expression was greatest at 22:00, exceeding that observed at 4:00, 10:00 and 16:00 by 3.59, 4.44 and 11.14-fold, respectively. Finally, the expression of NKA-α and SLC26A6 protein at the single cell level was also higher at night than during the day, which was 1.65-fold and 1.37-fold higher at 22:00 respectively compared to 16:00. Overall, the present findings revealed that naked carp drinks at night and feeds during the day, demonstrating that intestinal ion regulation exhibits a daily rhythm when exposed to high saline and alkaline lake water.

Two general strategies exist for the growth and survival of prokaryotes in environments of elevated osmolarity. The ‘salt in cytoplasm’ approach, which requires extensive structural modifications, is restricted mainly to members of the Halobacteriaceae. All other species have convergently evolved to cope with environments of elevated osmolarity by the accumulation of a restricted range of low molecular mass molecules, termed compatible solutes owing to their compatibility with cellular processes at high internal concentrations. Herein we review the molecular mechanisms governing the accumulation of these compounds, both in Gram-positive and Gram-negative bacteria, focusing specifically on the regulation of their transport/synthesis systems and the ability of these systems to sense and respond to changes in the osmolarity of the extracellular environment. Finally, we examine the current knowledge on the role of these osmostress responsive systems in contributing to the virulence potential of a number of pathogenic bacteria.

The infraorder Brachyura (true or short-tailed crabs) represents a successful group of marine invertebrates yet with limited genomic resources. Here we report a chromosome-anchored reference genome and transcriptomes of the Chinese mitten crab Eriocheir sinensis , a catadromous crab and invasive species with wide environmental tolerance, strong osmoregulatory capacity and high fertility. We show the expansion of specific gene families in the crab, including F-ATPase, which enhances our knowledge on the adaptive plasticity of this successful invasive species. Our analysis of spatio-temporal transcriptomes and the genome of E. sinensis and other decapods shows that brachyurization development is associated with down-regulation of Hox genes at the megalopa stage when tail shortening occurs. A better understanding of the molecular mechanism regulating sexual development is achieved by integrated analysis of multiple omics. These genomic resources significantly expand the gene repertoire of Brachyura, and provide insights into the biology of this group, and Crustacea in general. Brachyurans, or crabs, are of commercial and ecological importance, but limited genomic resources exist. Here the authors present a chromosome-level genome and expression data for the Chinese mitten crab, to shed light on the biology of this group.

Plants experience changes in light intensity and quality due to variations in solar angle and shading from clouds and overlapping leaves. Stomatal opening to increasing irradiance is often an order of magnitude slower than photosynthetic responses, which can result in CO₂ diffusional limitations on leaf photosynthesis, as well as unnecessary water loss when stomata continue to open after photosynthesis has reached saturation. Stomatal opening to light is driven by two distinct pathways; the ‘red’ or photosynthetic response that occurs at high fluence rates and saturates with photosynthesis, and is thought to be the main mechanism that coordinates stomatal behaviour with photosynthesis; and the guard cell-specific ‘blue’ light response that saturates at low fluence rates, and is often considered independent of photosynthesis, and important for early morning stomatal opening. Here we review the literature on these complicated signal transduction pathways and osmoregulatory processes in guard cells that are influenced by the light environment. We discuss the possibility of tuning the sensitivity and magnitude of stomatal response to blue light which potentially represents a novel target to develop ideotypes with the ‘ideal’ balance between carbon gain, evaporative cooling, and maintenance of hydraulic status that is crucial for maximizing crop performance and productivity.

Sucrose (SUC) is a signaling molecule with multiple physiological functions. G protein is a kind of receptor that converts extracellular first messenger into intracellular second messenger. However, it is little known that SUC interplays with G protein signaling in maize thermotolerance. In this work, using maize seedlings as materials, the interplay between SUC and G protein signaling in maize thermotolerance was investigated. The results indicate that heat stress-decreased survival percentage and tissue viability of the seedlings was mitigated by SUC. Similarly, heat stress-increased malondialdehyde content and electrolyte leakage also was reduced by SUC. These findings show that SUC can potentially enhance thermotolerance in maize seedlings. Also, SUC-enhanced thermotolerance was abolished by suramin (G protein inhibitor) and N-ethylmaleimide (SUC transport inhibitor), but enhanced by 3-O-methyl-D-glucose (G protein activator), indicating the interplay of SUC and G protein signaling in maize thermotolerance. To investigate the possible mechanism behind SUC-G protein interaction in enhancing maize thermotolerance, osmoregulation in mesocotyls of seedlings were evaluated before and after heat stress. The results suggest that osmolytes (SUC, glucose, fructose, total soluble sugar, proline, and glycine betaine) contents in mesocotyls under non-heat and heat stress were increased by SUC in varying degrees. Likewise, the osmolyte-metabolizing enzymes (sucrose-phosphate synthase, sucrose synthase, pyrroline-5-carboxylate synthase, ornithine aminotransferase, betaine-aldehyde dehydrogenase, and trehalase) activities were enhanced by SUC. Analogously, ZmSPS1 , ZmSUS6 , ZmP5CS , ZmOAT , ZmBADH , and ZmTRE1 expression in mesocotyls was up-regulated by SUC to different extent. These findings illustrate that the functional crosstalk of sucrose and G protein signaling in maize thermotolerance by modulating osmoregulation system.