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Adverse environmental conditions are detrimental to plant growth and development. Acclimation to abiotic stress conditions involves activation of signaling pathways which often results in changes in gene expression via networks of transcription factors (TFs). Mediator is a highly conserved co-regulator complex and an essential component of the transcriptional machinery in eukaryotes. Some Mediator subunits have been implicated in stress-responsive signaling pathways; however, much remains unknown regarding the role of plant Mediator in abiotic stress responses. Here, we use RNA-seq to analyze the transcriptional response of Arabidopsis thaliana to heat, cold and salt stress conditions. We identify a set of common abiotic stress regulons and describe the sequential and combinatorial nature of TFs involved in their transcriptional regulation. Furthermore, we identify stress-specific roles for the Mediator subunits MED9, MED16, MED18 and CDK8, and putative TFs connecting them to different stress signaling pathways. Our data also indicate different modes of action for subunits or modules of Mediator at the same gene loci, including a co-repressor function for MED16 prior to stress. These results illuminate a poorly understood but important player in the transcriptional response of plants to abiotic stress and identify target genes and mechanisms as a prelude to further biochemical characterization.
Adverse environmental conditions are detrimental to plant growth and development. Acclimation to abiotic stress conditions involves activation of signaling pathways which often results in changes in gene expression via networks of transcription factors (TFs). Mediator is a highly conserved co-regulator complex and an essential component of the transcriptional machinery in eukaryotes. Some Mediator subunits have been implicated in stress-responsive signaling pathways; however, much remains unknown regarding the role of plant Mediator in abiotic stress responses. Here, we use RNA-seq to analyze the transcriptional response of Arabidopsis thaliana to heat, cold and salt stress conditions. We identify a set of common abiotic stress regulons and describe the sequential and combinatorial nature of TFs involved in their transcriptional regulation. Furthermore, we identify stress-specific roles for the Mediator subunits MED9, MED16, MED18 and CDK8, and putative TFs connecting them to different stress signaling pathways. Our data also indicate different modes of action for subunits or modules of Mediator at the same gene loci, including a co-repressor function for MED16 prior to stress. These results illuminate a poorly understood but important player in the transcriptional response of plants to abiotic stress and identify target genes and mechanisms as a prelude to further biochemical characterization.
The increased emphasis on labour market activation in many European countries has led to new forms of governance in recent decades. Primarily through qualitative data and document analysis, this article compares the restructuring of labour market service delivery in the UK and Germany. The comparison suggests the emergence of complex governance arrangements that seek to balance public regulation and accountability with the creation of room for market competition. As a result, we can observe in both countries a greater use of markets, but also of rules. While in both countries the relationships between different providers of labour market services can best be described as a mixture of cooperation and competition, differences exist in terms of instruments and the comprehensiveness of coordination initiatives. The findings suggest that the distinctions between governance models may be more important in theory than in practice, although the combinations of theoretical forms vary in different circumstances.
Role of GDF15 in active lifestyle induced metabolic adaptations and acute exercise response in mice
(2019)
Physical activity is an important contributor to muscle adaptation and metabolic health. Growth differentiation factor 15 (GDF15) is established as cellular and nutritional stress-induced cytokine but its physiological role in response to active lifestyle or acute exercise is unknown. Here, we investigated the metabolic phenotype and circulating GDF15 levels in lean and obese male C57BI/6J mice with long-term voluntary wheel running (VWR) intervention. Additionally, treadmill running capacity and exercise-induced muscle gene expression was examined in GDF15-ablated mice. Active lifestyle mimic via VWR improved treadmill running performance and, in obese mice, also metabolic phenotype. The post-exercise induction of skeletal muscle transcriptional stress markers was reduced by VWR. Skeletal muscle GDF15 gene expression was very low and only transiently increased post-exercise in sedentary but not in active mice. Plasma GDF15 levels were only marginally affected by chronic or acute exercise. In obese mice, VWR reduced GDF15 gene expression in different tissues but did not reverse elevated plasma GDF15. Genetic ablation of GDF15 had no effect on exercise performance but augmented the post exercise expression of transcriptional exercise stress markers (Atf3, Atf6, and Xbp1s) in skeletal muscle. We conclude that skeletal muscle does not contribute to circulating GDF15 in mice, but muscle GDF15 might play a protective role in the exercise stress response.
Polar nuclear migration is crucial during the development of diverse eukaryotes. In plants, root hair growth requires polar nuclear migration into the outgrowing hair. However, knowledge about the dynamics and the regulatory mechanisms underlying nuclear movements in root epidermal cells remains limited. Here, we show that both auxin and Rho-of-Plant (ROP) signaling modulate polar nuclear position at the inner epidermal plasma membrane domain oriented to the cortical cells during cell elongation as well as subsequent polar nuclear movement to the outer domain into the emerging hair bulge in Arabidopsis (Arabidopsis thaliana). Auxin signaling via the nuclear AUXIN RESPONSE FACTOR7 (ARF7)/ARF19 and INDOLE ACETIC ACID7 pathway ensures correct nuclear placement toward the inner membrane domain. Moreover, precise inner nuclear placement relies on SPIKE1 Rho-GEF, SUPERCENTIPEDE1 Rho-GDI, and ACTIN7 (ACT7) function and to a lesser extent on VTI11 vacuolar SNARE activity. Strikingly, the directionality and/or velocity of outer polar nuclear migration into the hair outgrowth along actin strands also are ACT7 dependent, auxin sensitive, and regulated by ROP signaling. Thus, our findings provide a founding framework revealing auxin and ROP signaling of inner polar nuclear position with some contribution by vacuolar morphology and of actin-dependent outer polar nuclear migration in root epidermal hair cells.
There is a wealth of evidence showing that increasing the distance between an argument and its head leads to more processing effort, namely, locality effects: these are usually associated with constraints in working memory (DLT: Gibson, 2000: activation-based model: Lewis and Vasishth, 2005). In SOV languages, however, the opposite effect has been found: antilocality (see discussion in Levy et al., 2013). Antilocality effects can be explained by the expectation based approach as proposed by Levy (2008) or by the activation-based model of sentence processing as proposed by Lewis and Vasishth (2005). We report an eye-tracking and a self-paced reading study with sentences in Spanish together with measures of individual differences to examine the distinction between expectation- and memory based accounts, and within memory-based accounts the further distinction between DLT and the activation-based model. The experiments show that (i) antilocality effects as predicted by the expectation account appear only for high-capacity readers; (ii) increasing dependency length by interposing material that modifies the head of the dependency (the verb) produces stronger facilitation than increasing dependency length with material that does not modify the head; this is in agreement with the activation-based model but not with the expectation account; and (iii) a possible outcome of memory load on low-capacity readers is the increase in regressive saccades (locality effects as predicted by memory-based accounts) or, surprisingly, a speedup in the self-paced reading task; the latter consistent with good-enough parsing (Ferreira et al., 2002). In sum, the study suggests that individual differences in working memory capacity play a role in dependency resolution, and that some of the aspects of dependency resolution can be best explained with the activation-based model together with a prediction component.
There is a wealth of evidence showing that increasing the distance between an argument and its head leads to more processing effort, namely, locality effects; these are usually associated with constraints in working memory (DLT: Gibson, 2000; activation-based model: Lewis and Vasishth, 2005). In SOV languages, however, the opposite effect has been found: antilocality (see discussion in Levy et al., 2013). Antilocality effects can be explained by the expectation-based approach as proposed by Levy (2008) or by the activation-based model of sentence processing as proposed by Lewis and Vasishth (2005). We report an eye-tracking and a self-paced reading study with sentences in Spanish together with measures of individual differences to examine the distinction between expectation- and memory-based accounts, and within memory-based accounts the further distinction between DLT and the activation-based model. The experiments show that (i) antilocality effects as predicted by the expectation account appear only for high-capacity readers; (ii) increasing dependency length by interposing material that modifies the head of the dependency (the verb) produces stronger facilitation than increasing dependency length with material that does not modify the head; this is in agreement with the activation-based model but not with the expectation account; and (iii) a possible outcome of memory load on low-capacity readers is the increase in regressive saccades (locality effects as predicted by memory-based accounts) or, surprisingly, a speedup in the self-paced reading task; the latter consistent with good-enough parsing (Ferreira et al., 2002). In sum, the study suggests that individual differences in working memory capacity play a role in dependency resolution, and that some of the aspects of dependency resolution can be best explained with the activation-based model together with a prediction component.
There is a wealth of evidence showing that increasing the distance between an argument and its head leads to more processing effort, namely, locality effects; these are usually associated with constraints in working memory (DLT: Gibson, 2000; activation-based model: Lewis and Vasishth, 2005). In SOV languages, however, the opposite effect has been found: antilocality (see discussion in Levy et al., 2013). Antilocality effects can be explained by the expectation-based approach as proposed by Levy (2008) or by the activation-based model of sentence processing as proposed by Lewis and Vasishth (2005). We report an eye-tracking and a self-paced reading study with sentences in Spanish together with measures of individual differences to examine the distinction between expectation- and memory-based accounts, and within memory-based accounts the further distinction between DLT and the activation-based model. The experiments show that (i) antilocality effects as predicted by the expectation account appear only for high-capacity readers; (ii) increasing dependency length by interposing material that modifies the head of the dependency (the verb) produces stronger facilitation than increasing dependency length with material that does not modify the head; this is in agreement with the activation-based model but not with the expectation account; and (iii) a possible outcome of memory load on low-capacity readers is the increase in regressive saccades (locality effects as predicted by memory-based accounts) or, surprisingly, a speedup in the self-paced reading task; the latter consistent with good-enough parsing (Ferreira et al., 2002). In sum, the study suggests that individual differences in working memory capacity play a role in dependency resolution, and that some of the aspects of dependency resolution can be best explained with the activation-based model together with a prediction component.
In a self-paced reading study on German sluicing, Paape (Paape, 2016) found that reading times were shorter at the ellipsis site when the antecedent was a temporarily ambiguous garden-path structure. As a post-hoc explanation of this finding, Paape assumed that the antecedent’s memory representation was reactivated during syntactic reanalysis, making it easier to retrieve. In two eye tracking experiments, we subjected the reactivation hypothesis to further empirical scrutiny. Experiment 1, carried out in French, showed no evidence in favor in the reactivation hypothesis. Instead, results for one out of the three types of garden-path sentences that were tested suggest that subjects sometimes failed to resolve the temporary ambiguity in the antecedent clause, and subsequently failed to resolve the ellipsis. The results of Experiment 2, a conceptual replication of Paape’s (Paape, 2016) original study carried out in German, are compatible with the reactivation hypothesis, but leave open the possibility that the observed speedup for ambiguous antecedents may be due to occasional retrievals of an incorrect structure.
In a self-paced reading study on German sluicing, Paape (Paape, 2016) found that reading times were shorter at the ellipsis site when the antecedent was a temporarily ambiguous garden-path structure. As a post-hoc explanation of this finding, Paape assumed that the antecedent’s memory representation was reactivated during syntactic reanalysis, making it easier to retrieve. In two eye tracking experiments, we subjected the reactivation hypothesis to further empirical scrutiny. Experiment 1, carried out in French, showed no evidence in favor in the reactivation hypothesis. Instead, results for one out of the three types of garden-path sentences that were tested suggest that subjects sometimes failed to resolve the temporary ambiguity in the antecedent clause, and subsequently failed to resolve the ellipsis. The results of Experiment 2, a conceptual replication of Paape’s (Paape, 2016) original study carried out in German, are compatible with the reactivation hypothesis, but leave open the possibility that the observed speedup for ambiguous antecedents may be due to occasional retrievals of an incorrect structure.