Hatching plasticity in a Southeast Asian tree frog mitigates submergence-induced mortality

Environmentally cued hatching has been well-documented in amphibians in response to a wide range of abiotic and biotic factors. The hatching of terrestrial amphibian eggs in response to flooding may be basal within the group, but amphibian lineages in tropical Asia and sub-Saharan Africa have not received as much attention as their Neotropical counterparts. We investigated submergence-induced hatching in Feihyla hansenae, a Rhacophorid tree frog with terrestrial eggs. We quantified natural rates of clutch submergence at our study site in Thailand. Using submergence experiments, we found that embryos are capable of hatching early to escape flooding, and that failure to hatch results in mortality. Among the embryos that were able to hatch early, only the earliest, youngest hatchlings experienced a trade-off in body size that persisted for 6 days, while later, older hatchlings were not significantly smaller than spontaneous hatchlings under control conditions. By incorporating our natural and experimental data into Monte Carlo methods to simulate and compare survival probabilities with and without hatching plasticity, we found an overall 3.1% increase in submergence survival due to hatching plasticity. Our findings support the idea that flooding-induced hatching is widespread across amphibians with terrestrial eggs and highlight the importance of researching understudied tropical regions. As climate change is projected to affect rainfall patterns, the ability of embryos to escape abiotic egg-stage threats may be an indicator of species' ability to flexibly navigate a changing environment.     

Exploring the structural basis for selenium/mercury antagonism in Allium fistulosum

While continuing efforts are devoted to studying the mutually protective effect of mercury and selenium in mammals, few studies have investigated the mercury-selenium antagonism in plants. In this study, we report the metabolic fate of mercury and selenium in Allium fistulosum (green onion) after supplementation with sodium selenite and mercuric chloride. Analysis of homogenized root extracts via capillary reversed phase chromatography coupled with inductively coupled plasma mass spectrometry (capRPLC-ICP-MS) suggests the formation of a mercury-selenium containing compound. Micro-focused synchrotron X-ray fluorescence mapping of freshly excised roots show Hg sequestered on the root surface and outlining individual root cells, while Se is more evenly distributed throughout the root. There are also discrete Hg-only, Se-only regions and an overall strong correlation between Hg and Se throughout the root. Analysis of the X-ray absorption near edge structure (XANES) spectra show a "background" of methylselenocysteine within the root with discrete spots of SeO(3)(2-), Se(0) and solid HgSe on the root surface. Mercury outlining individual root cells is possibly binding to sulfhydryl groups or plasma membrane or cell wall proteins, and in some places reacting with reduced selenium in the rhizosphere to form a mercury(ii) selenide species. Together with the formation of the root-bound mercury(ii) selenide species, we also report on the formation of cinnabar (HgS) and Hg(0) in the rhizosphere. The results presented herein shed light on the intricate chemical and biological processes occurring within the rhizosphere that influence Hg and Se bioavailability and will be instrumental in predicting the fate and assisting in the remediation of these metals in the environment and informing whether or not fruit and vegetable food selection from aerial plant compartments or roots from plants grown in Hg contaminated soils, are safe for consumption.     

p85 Associates with Unphosphorylated PTEN and the PTEN-Associated Complex

The lipid phosphatase PTEN functions as a tumor suppressor by dephosphorylating the D3 position of phosphoinositide-3,4,5-trisphosphate, thereby negatively regulating the phosphoinositide 3-kinase (PI3K)/AKT signaling pathway. In mammalian cells, PTEN exists either as a monomer or as a part of a >600-kDa complex (the PTEN-associated complex [PAC]). Previous studies suggest that the antagonism of PI3K/AKT signaling by PTEN may be mediated by a nonphosphorylated form of the protein resident within the multiprotein complex. Here we show that PTEN associates with p85, the regulatory subunit of PI3K. Using newly generated antibodies, we demonstrate that this PTEN-p85 association involves the unphosphorylated form of PTEN engaged within the PAC and also includes the p110β isoform of PI3K. The PTEN-p85 association is enhanced by trastuzumab treatment and linked to a decline in AKT phosphorylation in some ERBB2-amplified breast cancer cell lines. Together, these results suggest that integration of p85 into the PAC may provide a novel means of downregulating the PI3K/AKT pathway.The phosphoinositide 3-kinase (PI3K)/AKT signaling pathway regulates glucose/nutrient homeostasis and cell survival and plays a central role in both normal metabolism and cancer. The PTEN tumor suppressor gene (29, 30, 54) negatively regulates the PI3K/AKT pathway by dephosphorylating the D3 hydroxyl subunit of phosphoinositide-3,4,5-trisphosphate, a key membrane phosphatidylinositol generated by PI3K (34). PTEN undergoes genetic or epigenetic inactivation in many malignancies, including glioblastoma, melanoma, and endometrial, prostate, and breast cancers, among others (6, 13, 22, 23, 47, 49-51, 55, 68). Similarly, germ line mutations of PTEN are associated with the development of hamartomatous neoplasias such as Cowden disease and Bannayan-Zonana syndrome (17, 21, 41).The tumor suppressor function of PTEN undergoes dynamic regulation involving both C-terminal phosphorylation and protein-protein interactions. Phosphorylation of serine and threonine residues at the PTEN C-terminal tail, mediated by kinases such as CK2 and glycogen synthase kinase 3β, alters its conformational structure and association with PDZ domain-containing proteins and attenuates PTEN enzymatic activity (1, 11, 20, 32, 45, 61-63, 66, 67, 71). Conversely, PTEN function is promoted in large part through its stabilization in unphosphorylated form by incorporation into a high-molecular-weight protein complex (the PTEN-associated complex [PAC]) (66). We first demonstrated the existence of the PAC through gel filtration studies of rat liver extracts, which identified PTEN within a high-molecular-mass peak (>600 kDa), as well as a low-molecular-mass peak (40 to 100 kDa) in which PTEN is monomeric and phosphorylated (66). Subsequently, several PDZ domain-containing proteins were shown to interact with PTEN, including MAGI-1b, MAGI-2, MAGI-3, ghDLG, hMAST205, MSP58/MCRS1, NHERF1, and NHERF2, which mediate indirect binding with platelet-derived growth factor (PDGF) receptor β (25, 36, 42, 57, 66). More recently, LKB1, a serine/threonine kinase tumor suppressor (7), was also found to interact with and phosphorylate PTEN in vitro (36). In aggregate, these data suggest that PTEN functional output is controlled by a complex interplay of protein interactions and regulation of C-terminal phosphorylation.Beyond these interactions, there is also evidence to support additional regulatory mechanisms by which the tumor suppressor function of PTEN is mediated. The herpesvirus-associated ubiquitin-specific protease was shown to interact directly with PTEN and promote its nuclear entry (53). Both ubiquitination and relocalization into the nucleus constitute important PTEN regulatory mechanisms (53, 64). In many tumors, PTEN nuclear exclusion has been associated with poor cancer prognosis and more aggressive cancer development (15, 44, 56). Moreover, successful treatment of acute promyelocytic leukemia was shown to be associated with an increase in monoubiquitinylation and relocation of PTEN into the nucleus (53).Like PTEN, the p85 regulatory subunit of PI3K serves as a prominent modulator of PI3K/AKT signaling. p85, which exists in three isoforms (α, β, and γ), targets the catalytic (110-kDa) PI3K subunit to the membrane, which brings it into proximity with membrane-associated phosphatidylinositol lipids. In the steady state, p85 forms a tight association with the catalytic PI3K subunit, usually p110α or p110β in nonhematopoietic cells, with p110δ predominating in leukocytes (19). Consistent with this notion, p85 and p110 exist in equimolar ratios in a wide variety of mammalian cell lines and tissues (19), although some studies have suggested a role for free p85 in cell signaling (33, 65).Several recent lines of evidence have begun to support a possible regulatory relationship between PTEN and p85 (reviewed in references 3 and 53). For example, liver-specific deletion of PIK3R1, which encodes the p85α regulatory subunit, reduces both the activation of PI3K and PTEN enzymatic activity in this context. As a result, p85α-deficient hepatic cells express elevated levels of phosphoinositide trisphosphate and exhibit prolonged AKT activation (60). In addition, both PTEN and p85 are regulated by small GTPase proteins such as RhoA, but PTEN coimmunoprecipitates with the RhoA effector Rock only in the presence of PI3K (18, 31, 37). Although only correlative in nature, these findings may suggest a possible role for PTEN in p85 regulation or vice versa, in addition to its known function as a direct antagonist of the PI3K/AKT pathway (3, 9, 52, 57, 60).In the present study, we demonstrate an endogenous association between p85 and PTEN. Using newly generated antibodies that selectively recognize the PTEN C-terminal tail in its unphosphorylated form, we demonstrate that this PTEN-p85 association preferentially involves the unphosphorylated form of PTEN. The specificity of this interaction was confirmed using multiple antibodies and through studies of both human cancer cells and murine embryonic fibroblasts (MEFs) deficient for specific p85 subunits. This association, which also engages p110β, is enhanced by trastuzumab treatment and correlates with diminished AKT phosphorylation. These results support a functional role for the PTEN-p85 association that may have important biological and therapeutic implications for PI3K/AKT pathway regulation.     

Shoot specific fungal endophytes alter soil phosphorus (P) fractions and potential acid phosphatase activity but do not increase P uptake in tall fescue

Aims

An experiment was performed to test how different fungal endophyte strains influenced tall fescue’s ability to access P from four P sources varying in solubility.

Methods

Novel endophyte infected (AR542E+ or AR584E+), common toxic endophyte infected (CTE+), or endophyte-free (E-) tall fescues were grown for 90 days in acidic soils amended with 30 mg kg^?1 P of potassium dihydrogen phosphate (KH₂PO₄), iron phosphate (FePO₄), aluminum phosphate (AlPO₄), or tricalcium phosphate ((Ca₃(PO₄)₂), respectively.

Results

Phosphorus form strongly influenced plant biomass, P acquisition, agronomic P use efficiency, microbial communities, P fractions. P uptake and vegetative biomass were similar for plants grown with AlPO₄, Ca₃(PO₄)₂, and KH₂PO₄ but greater than in control and FePO₄ soils. Infection with AR542E+ resulted in significantly less shoot biomass than CTE+ and E- varieties; there was no influence of endophyte on root biomass. The biomarker for arbuscular mycorrhizal fungi (AM fungi, 16:1ω5c) was selected as an effective predictor of variations in P uptake and tall fescue biomass. Potential acid phosphatase activity was strongly influenced by endophyte x P form interaction.

Conclusions

Endophyte infection in tall fescue significantly affected the NaOH-extractable inorganic P fraction, but had little detectable influence on soil microbial community structure, root biomass, or P uptake.

     

The hyperaccumulator Alyssum murale uses complexation with nitrogen and oxygen donor ligands for Ni transport and storage

The Kotodesh genotype of the nickel (Ni) hyperaccumulator Alyssum murale was examined to determine the compartmentalization and internal speciation of Ni, and other elements, in an effort to ascertain the mechanism used by this plant to tolerate extremely high shoot (stem and leaf) Ni concentrations. Plants were grown either hydroponically or in Ni enriched soils from an area surrounding an historic Ni refinery in Port Colborne, Ontario, Canada. Electron probe micro-analysis (EPMA) and synchrotron based micro X-ray fluorescence (μ-SXRF) spectroscopy were used to determine the metal distribution and co-localization and synchrotron X-ray and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopies were used to determine the Ni speciation in plant parts and extracted sap. Nickel is concentrated in the dermal leaf and stem tissues of A. murale bound primarily to malate along with other low molecular weight organic ligands and possibly counter anions (e.g., sulfate). Ni is present in the plant sap and vasculature bound to histidine, malate and other low molecular weight compounds. The data presented herein supports a model in which Ni is transported from the roots to the shoots complexed with histidine and stored within the plant leaf dermal tissues complexed with malate, and other low molecular weight organic acids or counter-ions.