Elevated [CO2] effects on crops: Advances in understanding acclimation,nitrogen dynamics and interactions with drought and other organisms

Future rapid increases in atmospheric CO₂ concentration [CO₂] are expected, with values likely to reach ~550 ppm by mid‐century. This implies that every terrestrial plant will be exposed to nearly 40% more of one of the key resources determining plant growth. In this review we highlight selected areas of plant interactions with elevated [CO₂] (e[CO₂]), where recently published experiments challenge long‐held, simplified views. Focusing on crops, especially in more extreme and variable growing conditions, we highlight uncertainties associated with four specific areas. (1) While it is long known that photosynthesis can acclimate to e[CO₂], such acclimation is not consistently observed in field experiments. The influence of sink–source relations and nitrogen (N) limitation on acclimation is investigated and current knowledge about whether stomatal function or mesophyll conductance (g_m) acclimate independently is summarised. (2) We show how the response of N uptake to e[CO₂] is highly variable, even for one cultivar grown within the same field site, and how decreases in N concentrations ([N]) are observed consistently. Potential mechanisms contributing to [N] decreases under e[CO₂] are discussed and proposed solutions are addressed. (3) Based on recent results from crop field experiments in highly variable, non‐irrigated, water‐limited environments, we challenge the previous opinion that the relative CO₂ effect is larger under drier environmental conditions. (4) Finally, we summarise how changes in growth and nutrient concentrations due to e[CO₂] will influence relationships between crops and weeds, herbivores and pathogens in agricultural systems.     

Phylum‐wide general protein O‐glycosylation system of the Bacteroidetes

The human gut symbiont Bacteroides fragilis has a general protein O‐glycosylation system in which numerous extracytoplasmic proteins are glycosylated at a three amino acid motif. In B. fragilis, protein glycosylation is a fundamental and essential property as mutants with protein glycosylation defects have impaired growth and are unable to competitively colonize the mammalian intestine. In this study, we analysed the phenotype of B. fragilis mutants with defective protein glycosylation and found that the glycan added to proteins is comprised of a core glycan and an outer glycan. The genetic region encoding proteins for the synthesis of the outer glycan is conserved within a Bacteroides species but divergent between species. Unlike the outer glycan, an antiserum raised to the core glycan reacted with all Bacteroidetes species tested, from all four classes of the phylum. We found that diverse Bacteroidetes species synthesize numerous glycoproteins and glycosylate proteins at the same three amino acid motif. The wide‐spread conservation of this protein glycosylation system within the phylum suggests that this system of post‐translational protein modification evolved early, before the divergence of the four classes of Bacteroidetes, and has been maintained due to its physiological importance to the diverse species of this phylum.     

The hydrophobic substituent in aminophospholipids affects the formation kinetics of their Schiff bases

Schiff bases (SBs) are the initial products of non-enzymatic glycation reactions, which are associated to some diabetes-related diseases. In this work, we used physiological pH and temperature conditions to study the formation kinetics of the SBs of 1,2-dihexanoyl-sn-glycero-3-phosphoethanolamine (DPHE) and 1,2-dihexanoyl-sn-glycero-3-phospho-l-serine (DHPS) with various glycating compounds and with pyridoxal 5’-phosphate (an effective glycation inhibitor). Based on the obtained results, the hydrophobic environment simultaneously decreases the nucleophilic character of the amino group (k₁) and increases its pK_a, thereby increasing the formation rate of SB (k_obs). Therefore, the presence of hydrophobic chains in aminophospholipids facilitates the formation and stabilization of SBs, and also, in a biological environment, their glycation. Additionally, the results confirm the inhibitory action of B₆ vitamers on aminophospholipid glycation.     

Metal ion binding patterns of acyclovir: molecular recognition between this antiviral agent and copper(II) chelates with iminodiacetate or glycylglycinate

In order to deepen on metal-binding patterns of acyclovir (acv), {[Cu(IDA)(acv)]·2MeOH}_n (1) and [Cu(glygly)(acv)]·H₂O (2) compounds have been synthesized and investigated by X-ray crystallography as well as spectral and thermal methods. These compounds have been chosen upon the assumption that iminodiacetate (IDA) and glycylglycinate (glygly) chelating ligands would bind copper(II) with mer-tridentate conformation, supplying two terminal H-acceptor carboxylate groups (IDA) or one H-acceptor carboxylate and one H-donor primary amino group (glygly). The main aim of this work was to clarify if the amino group of glygly can build an intra-molecular interligand H-bonding interaction to reinforce the Cu―N7(acv) bond. Our results are discussed in the context of an up-to-date critical look regarding the related structural information. From the viewpoint of molecular recognition, the structure of 1 shows that the chelate-nucleoside recognition only involves the Cu―N7(acv) coordination bond. In contrast, the molecular complex of 2 exhibits the Cu―N7(acv) coordination bond reinforced by an intra-molecular (glygly)N-H···O6(acv) interaction (2.961(3) Å, 140.5°).     

Gene sequencing and tissue expression of unknown isoforms of an angiotensin II type 2 receptor interacting protein, ATIP, in the rat

To investigate the expression of the unknown angiotensin II type 2 receptor interacting protein (ATIP) isoforms in the rat we used the known sequences of human and mouse ATIP to design sequencing primers to enable us to sequence rat ATIP3 and ATIP4. Exon 4, which is present in human but not mouse ATIP, was not identified in the coding region of rat ATIP. The expression levels of these genes in a range of rat tissues were examined, and we concluded that there is little similarity in the relative tissue distribution of the various ATIP isoforms in rat and human.     

Lack of the antioxidant glutathione peroxidase-1 does not increase atherosclerosis in C57BL/J6 mice fed a high-fat diet

Oxidative stress is thought to contribute to the initiation and progression of atherosclerosis. As glutathione peroxidase-1 (Gpx1) is an antioxidant enzyme that detoxifies lipid hydroperoxides, we tested the impact of Gpx1 deficiency on atherosclerotic processes and antioxidant enzyme expression in mice fed a high-fat diet (HFD). After 12 weeks of HFD, atherosclerotic lesions at the aortic sinus were of similar size in control and Gpx1-deficient mice. However, after 20 weeks of HFD, lesion size increased further in control but not in Gpx1-deficient mice, even though plasma and aortic wall markers of oxidative damage did not differ between groups. In control mice, the expression of Gpx1 increased and that of Gpx3 decreased at the aortic sinus after 20 weeks of HFD, with no change in the expression of Gpx2, Gpx4, catalase, peroxiredoxin-6, glutaredoxin-1 and -2, or thioredoxin-1 and -2. By comparison, in Gpx1-deficient mice, the expression of antioxidant genes was unaltered except for a decrease in glutaredoxin-1 and an increase in glutaredoxin-2. These changes were associated with increased expression of the proinflammatory marker monocyte chemoattractant protein-1 in control mice but not in Gpx1-deficient mice. In summary, a specific deficiency in Gpx1 was not accompanied by an increase in markers of oxidative damage or increased atherosclerosis in a murine model of HFD-induced atherogenesis.     

Molecular modeling of Henry-Michaelis and acyl-enzyme complexes between imipenem and Enterobacter cloacae P99 beta-lactamase

We report a molecular-mechanics (AMBER*) study on the Henry-Michaelis complex and the corresponding acyl-enzyme adduct formed between imipenem (1), a transient inhibitor of beta-lactamases, and Enterobacter cloacae P99, a class C-beta-lactamase. We have examined the influence of the structural configuration of the functional groups in the substrate on their three-dimensional (3D) arrangement at the active site, which was compared with those adopted by typical penicillins and cephalosporins. Our results confirm that the carboxy group of the antibiotic plays a prominent role in the binding of the substrate to the active site, and that it activates Ser64 through interaction with the phenolic OH group of Tyr150. The binding of imipenem to E. cloacae P99 increases the distance between Tyr150 and Ser64 due to the presence of a hydrophobic Me group in the (R)-1-hydroxyethyl substituent at C(6). This, together with the 3D arrangement of its carboxy group, leads to an interaction with the active site in a manner that hinders H+ exchange between the nucleophile in Ser64 and its basic activator, the phenolic group of Tyr150.     

Actin-binding protein alpha-actinin-1 interacts with the metabotropic glutamate receptor type 5b and modulates the cell surface expression and function of the receptor

Receptors for neurotransmitters require scaffolding proteins for membrane microdomain targeting and for regulating receptor function. Using a yeast two-hybrid screen, alpha-actinin-1, a major F-actin cross-linking protein, was identified as a binding partner for the C-terminal domain of metabotropic glutamate receptor type 5b (mGlu(5b) receptor). Co-expression, co-immunoprecipitation, and pull-down experiments showed a close and specific interaction between mGlu(5b) receptor and alpha-actinin-1 in both transfected HEK-293 cells and rat striatum. The interaction of alpha-actinin-1 with mGlu(5b) receptor modulated the cell surface expression of the receptor. This was dependent on the binding of alpha-actinin-1 to the actin cytoskeleton. In addition, the alpha-actinin-1/mGlu(5b) receptor interaction regulated receptor-mediated activation of the mitogen-activated protein kinase pathway. Together, these findings indicate that there is an alpha-actinin-1-dependent mGlu(5b) receptor association with the actin cytoskeleton modulating receptor cell surface expression and functioning.     

A cost for high levels of sperm competition in rodents: increased sperm DNA fragmentation

Sperm competition, a prevalent evolutionary process in which the spermatozoa of two or more males compete for the fertilization of the same ovum, leads to morphological and physiological adaptations, including increases in energetic metabolism that may serve to propel sperm faster but that may have negative effects on DNA integrity. Sperm DNA damage is associated with reduced rates of fertilization, embryo and fetal loss, offspring mortality, and mutations leading to genetic disease. We tested whether high levels of sperm competition affect sperm DNA integrity. We evaluated sperm DNA integrity in 18 species of rodents that differ in their levels of sperm competition using the sperm chromatin structure assay. DNA integrity was assessed upon sperm collection, in response to incubation under capacitating or non-capacitating conditions, and after exposure to physical and chemical stressors. Sperm DNA was very resistant to physical and chemical stressors, whereas incubation in non-capacitating and capacitating conditions resulted in only a small increase in sperm DNA damage. Importantly, levels of sperm competition were positively associated with sperm DNA fragmentation across rodent species. This is the first evidence showing that high levels of sperm competition lead to an important cost in the form of increased sperm DNA damage.