Evaluation of glyphosate resistance in Arabidopsis thaliana expressing an altered target site EPSPS.

BACKGROUND: Glyphosate-resistant goosegrass has recently evolved and is homozygous for the double mutant of EPSPS (T102 I, P106 S or TIPS). These same mutations combined with EPSPS overexpression, have been used to create transgenic glyphosate-resistant crops. Arabidopsis thaliana (Wt EPSPS Ki ∼ 0.5 µM) was engineered to express a variant AtEPSPS-T102 I, P106 A (TIPA Ki = 150 µM) to determine the resistance magnitude for a more potent variant EPSPS that might evolve in weeds. RESULTS: Transgenic A. thaliana plants, homozygous for one, two or four copies of AtEPSPS-TIPA, had resistance (IC50 values, R/S) as measured by seed production ranging from 4.3- to 16-fold. Plants treated in reproductive stage were male sterile with a range of R/S from 10.1- to 40.6-fold. A significant hormesis (∼ 63% gain in fresh weight) was observed for all genotypes when treated at the initiation of reproductive stage with 0.013 kg ha-1 . AtEPSPS-TIPA enzyme activity was proportional to copy number and correlated with resistance magnitude. CONCLUSIONS: A. thaliana, as a model weed expressing one copy of AtEPSPS-TIPA (300-fold more resistant), had only 4.3-fold resistance to glyphosate for seed production. Resistance behaved as a single dominant allele. Vegetative tissue resistance was 4.7-fold greater than reproductive tissue resistance and was linear with gene copy number. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The contribution of spontaneous mutation to variation in environmental responses of Arabidopsis thaliana: responses to light.

It has been hypothesized that new, spontaneous mutations tend to reduce fitness more severely in more stressful environments. To address this hypothesis, we grew plants representing 20 Arabidopsis thaliana mutation-accumulation (M-A) lines, advanced to generation 17, and their progenitor, in differing light conditions. The experiment was conducted in a greenhouse, and two treatments were used: full sun and shade, in which influx of red light was reduced relative to far-red. The shade treatment was considered the more stressful because mean absolute fitness was lower in that treatment, though not significantly so. Plants from generation 17 of M-A developed significantly faster than those from generation 0 in both treatments. A significant interaction between generation and treatment revealed that, counter to the hypothesis, M-A lines tended to have higher fitness on average relative to the progenitor in the shaded conditions, whereas, in full sun, the two generations were similar in fitness. A secondary objective of this experiment was to characterize the contribution of new mutations to genotype x environment interaction. We did not, however, detect a significant interaction between M-A line and treatment. Plots of the line-specific environmental responses indicate no tendency of new mutations to contribute to fitness trade-offs, between environments. They also do not support a model of conditionally deleterious mutation, in which a mutant reduces fitness only in a particular environment. These results suggest that interactions between genotype and light environment previously documented for A. thaliana are not explicable primarily as a consequence of steady input of spontaneous mutations having environment-specific effects.

Spread of academic success in a high school social network.

Application of social network analysis to education has revealed how social network positions of K-12 students correlate with their behavior and academic achievements. However, no study has been conducted on how their social network influences their academic progress over time. Here we investigated correlations between high school students' academic progress over one year and the social environment that surrounds them in their friendship network. We found that students whose friends' average GPA (Grade Point Average) was greater (or less) than their own had a higher tendency toward increasing (or decreasing) their academic ranking over time, indicating social contagion of academic success taking place in their social network.