Sumoylation of AMPKβ2 subunit enhances AMP-activated protein kinase activity

AMP-activated protein kinase (AMPK) is a sensor of cellular energy status. It is a heterotrimer composed of a catalytic α and two regulatory subunits (β and γ). AMPK activity is regulated allosterically by AMP and by the phosphorylation of residue Thr-172 within the catalytic domain of the AMPKα subunit by upstream kinases. We present evidence that the AMPKβ2 subunit may be posttranslationally modified by sumoylation. This process is carried out by the E3-small ubiquitin-like modifier (SUMO) ligase protein inhibitor of activated STAT PIASy, which modifies the AMPKβ2 subunit by the attachment of SUMO2 but not SUMO1 moieties. Of interest, AMPKβ1 is not a substrate for this modification. We also demonstrate that sumoylation of AMPKβ2 enhances the activity of the trimeric α2β2γ1 AMPK complex. In addition, our results indicate that sumoylation is antagonist and competes with the ubiquitination of the AMPKβ2 subunit. This adds a new layer of complexity to the regulation of the activity of the AMPK complex, since conditions that promote ubiquitination result in inactivation, whereas those that promote sumoylation result in the activation of the AMPK complex.     

Pollen limitation and fruit abortion in a declining rare tree,the Eurasian yew (Taxus baccata L.): A reproductive cost of ecological marginality

Populations of rare tree species such as the dioecious and anemophilous yew (Taxus baccata) are especially prone to extinction if they occupy marginal habitats. This is the case of yew populations growing in Mediterranean mountains under dry climate and a severe anthropogenic disturbance regime, which show insufficient regeneration. We examined two of the likely mechanisms driving this population decline. The study was conducted in a central Spanish yew population in 2005 and 2006. On one hand, we tested for the effect of the amount of pollen received by female flowers by means of a pollen addition experiment. On the other hand, we tested for the effect of initial fruit set on abortion and mature fruit production. Finally, we evaluated the effect of the spatial arrangement of male and female yew trees on realized fecundity. The success of fertilization and fruiting in the experimental population was pollen-limited. Female trees aborted ca. 70% of the fruit set in both years and treatments. Fruit set was significantly influenced by the females' neighbourhood, with fecundity decreasing exponentially with distance to the nearest male in both years. Overall, our results indicate that factors associated with ecological marginality have a strong influence on yew performance.     

Increased dosage of Ink4/Arf protects against glucose intolerance and insulin resistance associated with aging

Recent genome‐wide association studies have linked type‐2 diabetes mellitus to a genomic region in chromosome 9p21 near the Ink4/Arf locus, which encodes tumor suppressors that are up‐regulated in a variety of mammalian organs during aging. However, it is unclear whether the susceptibility to type‐2 diabetes is associated with altered expression of the Ink4/Arf locus. In the present study, we investigated the role of Ink4/Arf in age‐dependent alterations of insulin and glucose homeostasis using Super‐Ink4/Arf mice which bear an extra copy of the entire Ink4/Arf locus. We find that, in contrast to age‐matched wild‐type controls, Super‐Ink4/Arf mice do not develop glucose intolerance with aging. Insulin tolerance tests demonstrated increased insulin sensitivity in Super‐Ink4/Arf compared with wild‐type mice, which was accompanied by higher activation of the insulin receptor substrate (IRS)‐PI3K‐AKT pathway in liver, skeletal muscle and heart. Glucose uptake studies in Super‐Ink4/Arf mice showed a tendency toward increased ¹⁸F‐fluorodeoxyglucose uptake in skeletal muscle compared with wild‐type mice (P = 0.079). Furthermore, a positive correlation between glucose uptake and baseline glucose levels was observed in Super‐Ink4/Arf mice (P < 0.008) but not in wild‐type mice. Our studies reveal a protective role of the Ink4/Arf locus against the development of age‐dependent insulin resistance and glucose intolerance.     

Genetic characterization of the invasive mosquitofish (Gambusia spp.) introduced to Europe: population structure and colonization routes

Biological invasions are considered one of the main anthropogenic factors that reduce the abundance of native species. Understanding the patterns of population structure and behavior of introduced species is important to determine invasion sources and pathways, in addition to improving the protective management of native species. Thus, we set out to advance our knowledge about the mosquitofish Gambusia spp., which is an invasive species that was introduced to southern Europe in 1921 to control mosquito populations. We assessed the genetic diversity and population structure of this species at 13 European locations, by screening variation at six microsatellite loci. We also evaluated six American samples (four of G. holbrooki and two of G. affinis) to identify the most likely source of the populations that established in Europe, and to determine whether G. affinis is also present. The results showed that, while there was evidence of recent bottleneck events in a few isolated locations, most introduced populations harbored a considerable amount of gene diversity, probably because of multiple introductions and secondary contacts. Populations displayed strong genetic differentiation that was mainly associated with geographical distance. At least two main routes of colonization of G. holbrooki seem to have occurred in Europe. The first, and more ancient colonization, was consistent with historical records, with the species invading the Iberian Peninsula. A second and more recent colonization probably occurred in Greece and, from there, France. The presence of G. affinis was not detected in any of the European samples.     

Intraspecific competition replaces interspecific facilitation as abiotic stress decreases: The shifting nature of plant–plant interactions

Plant–plant interactions change depending on environmental conditions, shifting from competition to facilitation when the stress is high. In addition to these changes, the relevance of intraspecific compared to interspecific interactions may also shift as abiotic stress does. We inferred intra- and interspecific plant–plant interactions of the cushion plant Hormathophylla spinosa as related to the dominant shrub Juniperus sabina in two sites with contrasting abiotic conditions (a slope with high-stress conditions vs. a valley bottom with milder conditions) in a Mediterranean high mountain. Specifically, we studied the spatial patterns and several variables related to plant performance (plant size and form, non-structural carbohydrate – NSC – concentrations and radial growth) of H. spinosa.The spatial pattern varied depending on site conditions. H. spinosa plants were positively associated with juniper in the high-stress slope site, probably through higher establishment rates due to the amelioration of soil conditions. In contrast, in the milder valley site H. spinosa establishment occurred mostly in open areas. Age structure, inferred from annual rings, reflected a massive establishment event in the whole study area which occurred 30–50 years ago. Canopy variables and radial growth were density dependent: both were negatively affected by the high density of H. spinosa individuals in the valley, but favoured by junipers on the slope. Interestingly, NSCs showed the opposite pattern, suggesting lower investment in growth by H. spinosa plants in the valley than on the slope.Our results reinforce the strong links existing between intra- and interspecific relationships and the need to include both when studying the influence of abiotic conditions on plant–plant interactions. This approach enabled us to detect that the direction and intensity of plant–plant interactions may shift at different ecological levels. Particularly interesting was the finding that optimal sites at the population level may not necessarily be the sites showing maximum individual performance.     

Insulin-Receptor Substrate-2 (IRS-2) Is Required for Maintaining Glucokinase and Glucokinase Regulatory Protein Expression in Mouse Liver

Insulin receptor substrate (IRS) proteins play important roles in hepatic nutrient homeostasis. Since glucokinase (GK) and glucokinase regulatory protein (GKRP) function as key glucose sensors, we have investigated the expression of GK and GKRP in liver of Irs-2 deficient mice and Irs2(−/−) mice where Irs2 was reintroduced specifically into pancreatic β-cells [RIP-Irs-2/IRS-2(−/−)]. We observed that liver GK activity was significantly lower (p<0.0001) in IRS-2(−/−) mice. However, in RIP-Irs-2/IRS-2(−/−) mice, GK activity was similar to the values observed in wild-type animals. GK activity in hypothalamus was not altered in IRS-2(−/−) mice. GK and GKRP mRNA levels in liver of IRS-2(−/−) were significantly lower, whereas in RIP-Irs-2/IRS-2(−/−) mice, both GK and GKRP mRNAs levels were comparable to wild-type animals. At the protein level, the liver content of GK was reduced in IRS-2(−/−) mice as compared with controls, although GKRP levels were similar between these experimental models. Both GK and GKRP levels were lower in RIP-Irs-2/IRS-2(−/−) mice. These results suggest that IRS-2 signalling is important for maintaining the activity of liver GK. Moreover, the differences between liver and brain GK may be explained by the fact that expression of hepatic, but not brain, GK is controlled by insulin. GK activity was restored by the β-cell compensation in the RIP-Irs-2/IRS-2 mice. Interestingly, GK and GKRP protein expression remained low in RIP-Irs-2/IRS-2(−/−) mice, perhaps reflecting different mRNA half-lives or alterations in the process of translation and post-translational regulation.     

Chronic mild salinity affects source leaves physiology and productivity parameters of rice plants (Oryza sativa L., cv. Taipei 309)

Aim

In rice, the top two leaves are the major carbohydrate source during grain filling. Physiological performance of these leaves under salinity may allow estimate stress-induced yield loss.

Methods

Greenhouse grown rice plants (cv. Taipei 309) were subjected to 10 and 20 mM NaCl stress levels from germination till maturity. Plant development was measured at the flowering stage and yield parameters were quantified after complete ripening of panicles.

Results

Gas exchange in the main source leaves were not significantly affected by any of the stress levels. However, growth parameters as well as total metabolizable carbohydrates content, chlorophyll content (CCI), maximal efficiency of PSII photochemistry in dark-adapted state (F _v/F _m) and lipid peroxidation were significantly affected. Rice yield, measured as total panicle production, declined to 78 and 21 % of controls in 10 and 20 mM NaCl stress, respectively. Stress-induced yield loss was positively related with the decline in CCI, F _v/F _m and K⁺/Na⁺ ratio as well as with the increase in lipid peroxidation and total soluble carbohydrate contents.

Conclusions

Though the stress levels used in this work are below what is considered the minimal critical threshold of toxicity for rice, they induce significant negative effects on plant development and yield, when present along the whole plant life cycle.     

The Impact of Global Change Factors on Redox Signaling Underpinning Stress Tolerance

The plant cuticle is an extracellular hydrophobic layer that covers the aerial epidermis of all land plants, providing protection against desiccation and external environmental stresses. The past decade has seen considerable progress in assembling models for the biosynthesis of its two major components, the polymer cutin and cuticular waxes. Most recently, two breakthroughs in the long-sought molecular bases of alkane formation and polyester synthesis have allowed construction of nearly complete biosynthetic pathways for both waxes and cutin. Concurrently, a complex regulatory network controlling the synthesis of the cuticle is emerging. It has also become clear that the physiological role of the cuticle extends well beyond its primary function as a transpiration barrier, playing important roles in processes ranging from development to interaction with microbes. Here, we review recent progress in the biochemistry and molecular biology of cuticle synthesis and function and highlight some of the major questions that will drive future research in this field.The first plant colonizers of land, approximately 450 million years ago in the mid-Paleozoic era, faced a daunting set of challenges associated with their new terrestrial environment, including desiccation, temperature extremes, gravity, and increased exposure to UV radiation (Waters, 2003; Leliaert et al., 2011). The transition from an exclusively aquatic to a terrestrial life style, therefore, would have necessitated the evolution of a toolbox of morphological and physiological features, some of which are apparent through studies of the fossil record or by examining extant plant lineages. For example, the development of architecturally complex cell walls for biomechanical support and structural protection, which typify modern land plants, can be traced back to divergence and radiation within the Charophycean green algae, their immediate ancestors (Sørensen et al., 2011). However, the most critical adaptive trait for survival during terrestrialization would have been the ability to retain water in increasingly dehydrating habitats. Consequently, the capacity to synthesize, deposit, and maintain a hydrophobic surface layer, or cuticle, over the surfaces of aerial organs was arguably one of the most important innovations in the history of plant evolution. This idea is borne out by both fossil evidence (Edwards, 1993) and the ubiquity of cuticles among all extant embryophytes, from bryophytes (Budke et al., 2012) to angiosperms.Armed with a protective skin, together with a range of adaptive strategies for acquiring and conserving water, as well as for avoiding or tolerating water stress, embryophytes now thrive in a wide range of desiccating environments (Ogburn and Edwards, 2010; Aroca et al., 2012; Delaux et al., 2012; Jones and Dolan, 2012; Obata and Fernie, 2012; Gaff and Oliver, 2013). Accordingly, cuticles from a broad range of species, and in various ecological and agricultural contexts, have been studied from the perspective of their role as the primary barrier to transpirational water loss. However, it is now clear that cuticles play numerous other roles in plant development, physiology, and interactions with the abiotic environment and other organisms. Indeed, in recent years, there have been many instances of unexpected associations between the cuticle and diverse aspects of plant biology. In parallel, the past decade has seen considerable progress in understanding the biosynthesis of the major cuticle components and the complex regulatory networks that control cuticle synthesis and assembly.This review summarizes recent progress in elucidating the biochemistry and molecular biology of cuticle synthesis and function and highlights some of the connections to other aspects of plant biology, including signaling, pathogen defense, and development. Given the broad scope and space limitation, not every aspect of cuticle biosynthesis is covered in depth, and recent specialized reviews focusing on cuticle biomechanical properties (Domínguez et al., 2011), defensive functions (Reina-Pinto and Yephremov, 2009), and transport barrier properties (Burghardt and Riederer, 2006) may be of further interest. In addition, key ongoing questions in the field are discussed, and potential future approaches to resolving those questions are suggested.     

On the limitations of standard statistical modeling in biological systems: A full Bayesian approach for biology

One of the most important scientific challenges today is the quantitative and predictive understanding of biological function. Classical mathematical and computational approaches have been enormously successful in modeling inert matter, but they may be inadequate to address inherent features of biological systems. We address the conceptual and methodological obstacles that lie in the inverse problem in biological systems modeling. We introduce a full Bayesian approach (FBA), a theoretical framework to study biological function, in which probability distributions are conditional on biophysical information that physically resides in the biological system that is studied by the scientist.