Changes in photosynthetic electron transfer and state transitions in an herbicide-resistant D1 mutant from soybean cell cultures

Anomalies in photosynthetic activity of the soybean cell line STR7, carrying a single mutation (S268P) in the chloroplastic gene psbA that codes for the D1 protein of the photosystem II, have been examined using different spectroscopic techniques. Thermoluminescence emission experiments have shown important differences between STR7 mutant and wild type cells. The afterglow band induced by both white light flashes and far-red continuous illumination was downshifted by about 4 °C and the Q band was upshifted by 5 °C. High temperature thermoluminescence measurements suggested a higher level of lipid peroxidation in mutant thylakoid membranes. In addition, the reduction rate of P700⁺ was significantly accelerated in STR7 suggesting that the mutation led to an activation of the photosystem I cyclic electron flow. Modulated fluorescence measurements performed at room temperature as well as fluorescence emission spectra at 77 K revealed that the STR7 mutant is defective in state transitions. Here, we discuss the hypothesis that activation of the cyclic electron flow in STR7 cells may be a mechanism to compensate the reduced activity of photosystem II caused by the mutation. We also propose that the impaired state transitions in the STR7 cells may be due to alterations in thylakoid membrane properties induced by a low content of unsaturated lipids.     

Association of the I148M/PNPLA3 variant with elevated alanine transaminase levels in normal-weight and overweight/obese Mexican children

Background and aims

Non-alcoholic fatty liver disease (NAFLD) and elevated alanine transaminase (ALT) levels are common in obese Hispanic adults and children. Recently, a PNPLA3 gene variant (I148M) was strongly associated with NAFLD and higher ALT levels in obese adults, including Hispanics. The aims of this study were to estimate the frequency of elevated ALT levels, and to address the influence of obesity and PNPLA3/I148M on ALT levels in a general population sample of Mexican school-aged children.

Methods

A total of 1037 non-related Mexican children aged 6 to 12 years were genotyped for the I148M variant. Anthropometric, clinical and metabolic parameters were collected from all participants.

Results

Elevated ALT levels (> 35 U/L) were more frequent in obese (26.9%) and overweight (9.3%) than in normal weight children (2.2%). The M148M genotype was significantly associated with elevated ALT levels in this population (OR = 3.7, 95% CI 2.3–5.9; P = 3.7 × 10^− 8), and children carrying the M148M genotype showed significantly lower HDL cholesterol levels and BMI z-core (P = 0.036 and 0.015, respectively). On stratifying by BMI percentile, this genotype conferred a much greater risk of elevated ALT levels in normal weight (OR = 19.9, 95% CI 2.5–157.7; P = 0.005) than overweight and obese children (OR = 3.4, 95% CI 1.3–8.9; P = 0.014 and OR = 3.1, 95% CI 1.7–5.5; P = 1.4 x10^− 4, respectively).

Conclusions

The I148M PNPLA3 variant is strongly associated with elevated ALT levels in normal weight and overweight/obese Mexican children. Thus, the M148M genotype may be considered as an important risk factor for liver damage in this population.     

Natural selection fails to optimize mutation rates for long-term adaptation on rugged fitness landscapes

The rate of mutation is central to evolution. Mutations are required for adaptation, yet most mutations with phenotypic effects are deleterious. As a consequence, the mutation rate that maximizes adaptation will be some intermediate value. Here, we used digital organisms to investigate the ability of natural selection to adjust and optimize mutation rates. We assessed the optimal mutation rate by empirically determining what mutation rate produced the highest rate of adaptation. Then, we allowed mutation rates to evolve, and we evaluated the proximity to the optimum. Although we chose conditions favorable for mutation rate optimization, the evolved rates were invariably far below the optimum across a wide range of experimental parameter settings. We hypothesized that the reason that mutation rates evolved to be suboptimal was the ruggedness of fitness landscapes. To test this hypothesis, we created a simplified landscape without any fitness valleys and found that, in such conditions, populations evolved near-optimal mutation rates. In contrast, when fitness valleys were added to this simple landscape, the ability of evolving populations to find the optimal mutation rate was lost. We conclude that rugged fitness landscapes can prevent the evolution of mutation rates that are optimal for long-term adaptation. This finding has important implications for applied evolutionary research in both biological and computational realms.     

Genetic Structure and Molecular Variability of Cucumber mosaic virus Isolates in the United States

Cucumber mosaic virus (CMV) has a worldwide distribution and the widest host range of any known plant virus. From 2000 to 2012, epidemics of CMV severely affected the production of snap bean (Phaseulos vulgaris L.) in the Midwest and Northeastern United States. Virus diversity leading to emergence of new strains is often considered a significant factor in virus epidemics. In addition to epidemics, new disease phenotypes arising from genetic exchanges or mutation can compromise effectiveness of plant disease management strategies. Here, we captured a snapshot of genetic variation of 32 CMV isolates collected from different regions of the U.S including new field as well as historic isolates. Nucleotide diversity (π) was low for U.S. CMV isolates. Sequence and phylogenetic analyses revealed that CMV subgroup I is predominant in the US and further showed that the CMV population is a mixture of subgroups IA and IB. Furthermore, phylogenetic analysis suggests likely reassortment between subgroups IA and IB within five CMV isolates. Based on phylogenetic and computational analysis, recombination between subgroups I and II as well as IA and IB in RNA 3 was detected. This is the first report of recombination between CMV subgroups I and II. Neutrality tests illustrated that negative selection was the major force operating upon the CMV genome, although some positively selected sites were detected for all encoded proteins. Together, these data suggest that different regions of the CMV genome are under different evolutionary constraints. These results also delineate composition of the CMV population in the US, and further suggest that recombination and reassortment among strain subgroups does occur but at a low frequency, and point towards CMV genomic regions that differ in types of selection pressure.     

A library of linear undecapeptides with bactericidal activity against phytopathogenic bacteria

A 125-member library of synthetic linear undecapeptides was prepared based on a previously described peptide H-K¹KLFKKILKF¹⁰L-NH₂ (BP76) that inhibited in vitro growth of the plant pathogenic bacteria Erwinia amylovora, Xanthomonas axonopodis pv. vesicatoria, and Pseudomonas syringae pv. syringae at low micromolar concentrations. Peptides were designed using a combinatorial chemistry approach by incorporating amino acids possessing various degrees of hydrophobicity and hydrophilicity at positions 1 and 10 and by varying the N-terminus. Library screening for in vitro growth inhibition identified 27, 40 and 113 sequences with MIC values below 7.5 μM against E. amylovora, P. syringae and X. axonopodis, respectively. Cytotoxicity, bactericidal activity and stability towards protease degradation of the most active peptides were also determined. Seven peptides with a good balance between antibacterial and hemolytic activities were identified. Several analogues displayed a bactericidal effect and low susceptibility to protease degradation. The most promising peptides were tested in vivo by evaluating their preventive effect of inhibition of E. amylovora infection in detached apple and pear flowers. The peptide H-KKLFKKILKYL-NH₂ (BP100) showed efficacies in flowers of 63–76% at 100 μM, being more potent than BP76 and only less effective than streptomycin, currently used for fire blight control.     

Genetic transformation via particle bombardment of Catharanthus roseus plants through adventitious organogenesis of buds

In vitro propagation of Catharanthus roseus was achieved using nodal explants. Bud induction was best on medium containing 1.0 mg benzyl aminopurine l^–1. Hardening of rooted shoots to soil was very successful with 98% survival. Genetically transformed C. roseus plantlets were obtained after bombardment of nodal explants, which were then micropropagated, with DNA coated particles with green fluorescent protein (GFP) or -glucuronidase (GUS) reporter genes. Histological studies showed that the gene insertion method proved effective with many cells and different tissues displaying the reporter gene signals, showing that gene expressions were rather stable.