This review focuses on the role of organelles and retrograde signalling during the response to abiotic stress conditions with emhasis on the recovery of cellular energy metabolism.
Abstract
...Chloroplast and mitochondria not only provide the energy to the plant cell but due to the sensitivity of organellar processes to perturbations caused by abiotic stress, they are also key cellular sensors of environmental fluctuations. Abiotic stresses result in reduced photosynthetic efficiency and thereby reduced energy supply for cellular processes. Thus, in order to acclimate to stress, plants must re-program gene expression and cellular metabolism to divert energy from growth and developmental processes to stress responses. To restore cellular energy homeostasis following exposure to stress, the activities of the organelles must be tightly co-ordinated with the transcriptional re-programming in the nucleus. Thus, communication between the organelles and the nucleus, so-called retrograde signalling, is essential to direct the energy use correctly during stress exposure. Stress-triggered retrograde signals are mediated by reactive oxygen species and metabolites including β-cyclocitral, MEcPP (2-C-methyl-d-erythritol 2,4-cyclodiphosphate), PAP (3ʹ-phosphoadenosine 5ʹ-phosphate), and intermediates of the tetrapyrrole biosynthesis pathway. However, for the plant cell to respond optimally to environmental stress, these stress-triggered retrograde signalling pathways must be integrated with the cytosolic stress signalling network. We hypothesize that the Mediator transcriptional co-activator complex may play a key role as a regulatory hub in the nucleus, integrating the complex stress signalling networks originating in different cellular compartments.
Transcriptional regulation is a key aspect of environmental stress responses. Heat stress induces transcriptional memory, i.e., sustained induction or enhanced re-induction of transcription, that ...allows plants to respond more efficiently to a recurrent HS. In light of more frequent temperature extremes due to climate change, improving heat tolerance in crop plants is an important breeding goal. However, not all heat stress-inducible genes show transcriptional memory, and it is unclear what distinguishes memory from non-memory genes. To address this issue and understand the genome and epigenome architecture of transcriptional memory after heat stress, we identify the global target genes of two key memory heat shock transcription factors, HSFA2 and HSFA3, using time course ChIP-seq.
HSFA2 and HSFA3 show near identical binding patterns. In vitro and in vivo binding strength is highly correlated, indicating the importance of DNA sequence elements. In particular, genes with transcriptional memory are strongly enriched for a tripartite heat shock element, and are hallmarked by several features: low expression levels in the absence of heat stress, accessible chromatin environment, and heat stress-induced enrichment of H3K4 trimethylation. These results are confirmed by an orthogonal transcriptomic data set using both de novo clustering and an established definition of memory genes.
Our findings provide an integrated view of HSF-dependent transcriptional memory and shed light on its sequence and chromatin determinants, enabling the prediction and engineering of genes with transcriptional memory behavior.
Activation of the plastid-encoded RNA polymerase is tightly controlled and involves a network of phosphorylation and, as yet unidentified, thiol-mediated events. Here, we characterize PLASTID REDOX ...INSENSITIVE2, a redox-regulated protein required for full PEP-driven transcription. PRIN2 dimers can be reduced into the active monomeric form by thioredoxins through reduction of a disulfide bond. Exposure to light increases the ratio between the monomeric and dimeric forms of PRIN2. Complementation of prin2-2 with different PRIN2 protein variants demonstrates that the monomer is required for light-activated PEP-dependent transcription and that expression of the nuclear-encoded photosynthesis genes is linked to the activity of PEP. Activation of PEP during chloroplast development likely is the source of a retrograde signal that promotes nuclear LHCB expression. Thus, regulation of PRIN2 is the thiol-mediated mechanism required for full PEP activity, with PRIN2 monomerization via reduction by TRXs providing a mechanistic link between photosynthetic electron transport and activation of photosynthetic gene expression.
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 purpose of this study was to identify characteristics of investigations of sexual abuse concerning vulnerable adults residing in facility settings that were associated with case substantiation. ...Data on 410 reports of sexual abuse were collected prospectively from Adult Protective Services (APS) and state licensure agency staff in New Hampshire, Oregon, Tennessee, Texas, and Wisconsin over a six-month period. Specifically, we examined differences between reports that were substantiated and those that were not by comparing characteristics of alleged victims, alleged perpetrators, and aspects of investigation using logistic regression. We found that a relatively low proportion of cases (18%) were substantiated overall. Compared to cases that were not substantiated, cases that were substantiated were more likely to feature nursing home residents, older victims, female victims, and allegations of physical contact between the alleged perpetrator and victim. Despite the high proportion of alleged perpetrators who were facility staff (51%) compared to resident perpetrators (25%), cases with resident-to-resident allegations of abuse were much more likely to be substantiated, accounting for 63% of substantiated cases. In light of these findings, we believe it is important that investigators are trained to handle sexual abuse cases appropriately and that they are able to investigate the case thoroughly, promptly, and with as much information as possible. It is also critical that investigators make substantiation decisions using the appropriate standard for confirmation (e.g., preponderance of the evidence, beyond a reasonable doubt, clear and convincing evidence) as state law dictates.
BACKGROUND:Although hypertension (HTN) treatment rates are similar across age groups of women, effective control is significantly worse among older women. Only 20% of hypertensive women aged 70 to 79 ...years have controlled blood pressure.
OBJECTIVES:The purpose of this longitudinal study was to test the effects of the quality of mother-daughter relationship, inner strength, and control on HTN self-management and health-related quality of life (HRQOL) for both members of the dyad at 6 months. The Actor-Partner Interdependence Model was used to examine the direct (“actor”) and indirect (“partner”) effects of 46 dyads.
RESULTS:The mothers’ perceived relationship quality with daughters directly impacted their own self-management of HTN and HRQOL while also indirectly affecting their daughters’ self-management. Similarly, the daughters’ perceived strength of their relationship with their mothers directly influenced their self-management and HRQOL and indirectly affected their mothers’ self-management and HRQOL.
Biogenesis of the photosystems in oxygenic phototrophs requires co-translational insertion of chlorophyll a. The first committed step of chlorophyll a biosynthesis is the insertion of a Mg(2+) ion ...into the tetrapyrrole intermediate protoporphyrin IX, catalyzed by Mg-chelatase. We have identified a Synechocystis sp. PCC 6803 strain with a spontaneous mutation in chlH that results in a Gly195 to Glu substitution in a conserved region of the catalytic subunit of Mg-chelatase. Mutant strains containing the ChlH Gly195 to Glu mutation were generated using a two-step protocol that introduced the chlH gene into a putative neutral site in the chromosome prior to deletion of the native gene. The Gly195 to Glu mutation resulted in strains with decreased chlorophyll a. Deletion of the PS II assembly factor Ycf48 in a strain carrying the ChlH Gly195 to Glu mutation did not grow photoautotrophically. In addition, the ChlH-G195E:ΔYcf48 strain showed impaired PS II activity and decreased assembly of PS II centers in comparison to a ΔYcf48 strain. We suggest decreased chlorophyll in the ChlH-G195E mutant provides a background to screen for the role of assembly factors that are not essential under optimal growth conditions.
Limited studies are done regarding ability to produce gastric acid in preterm infants and most studies used
method of assessing gastric pH.
To assess the feasibility of using an
method of measuring ...gastric pH in babies ≤ 28 weeks gestational age (GA) and determine whether changes in gastric pH differ with gestational age, mode of delivery, and use of antenatal steroids.
Prospective study that enrolled extremely low birth weight (ELBW) babies. Gastric aspirate collected before feeding.
testing of gastric aspirates for pH were done on days of life 1, 3, 5, 7, 14, and 28 by using pH electrode. The pH was measured on each sample in triplicate, mean calculated and used for data analysis. Stastical methods included descriptive statistics,
-tests and repeated measures ANOVA.
29 subjects ≤ 28 weeks or birth weight ≤ 1,000 g were enrolled. No significant change was noted in pH measurements over time. Antenatal steroids and mode of delivery did not affect gastric acid pH.
The
method for gastric pH measurements is non-invasive and affords more frequent testing. It would be useful in studying various conditions that may affect gastric pH.
Synechocystis sp. strain PCC 6803 grows photoautotrophically across a broad pH range, but wild-type cultures reach a higher density at elevated pH; however, photoheterotrophic growth is similar at ...high and neutral pH. A number of PSII mutants each lacking at least one lumenal extrinsic protein, and carrying a second PSII lumenal mutation, are able to grow photoautotrophically in BG-11 medium at pH 10.0, but not pH 7.5. We investigated the basis of this pH effect and observed no pH-specific change in variable fluorescence yield from PSII centers of the wild type or the pH-dependent ΔPsbO:ΔPsbU and ΔPsbV:ΔCyanoQ strains; however, 77 K fluorescence emission spectra indicated increased coupling of the phycobilisome (PBS) antenna at pH 10.0 in all mutants. DNA microarray data showed a cell-wide response to transfer from pH 10.0 to pH 7.5, including decreased mRNA levels of a number of oxidative stress-responsive transcripts. We hypothesize that this transcriptional response led to increased tolerance against reactive oxygen species and in particular singlet oxygen. This response enabled photoautotrophic growth of the PSII mutants at pH 10.0. This hypothesis was supported by increased resistance of all strains to rose bengal at pH 10.0 compared with pH 7.5.
In oxygenic photosynthesis, the D1 protein of Photosystem II is the primary target of photodamage and environmental stress can accelerate this process. The cyanobacterial response to stress includes ...transcriptional regulation of genes encoding D1, including low‐oxygen‐induction of psbA1 encoding the D1´ protein in Synechocystis sp. PCC 6803. The psbA1 gene is also transiently up‐regulated in high light, and its deletion has been reported to increase ammonium‐induced photoinhibition. Therefore we investigated the role of D1´‐containing PS II centres under different environmental conditions. A strain containing only D1´‐PS II centres under aerobic conditions exhibited increased sensitivity to ammonium chloride and high light compared to a D1‐containing strain. Additionally a D1´‐PS II strain was outperformed by a D1‐PS II strain under normal conditions; however, a strain containing low‐oxygen‐induced D1´‐PS II centres was more resilient under high light than an equivalent D1 strain. These D1´‐containing centres had chlorophyll a fluorescence characteristics indicative of altered forward electron transport and back charge recombination with the donor side of PS II. Our results indicate D1´‐PS II centres are important in the reconfiguration of thylakoid electron transport in response to high light and low oxygen.
In oxygenic photosynthesis, the D1 protein of Photosystem II is the primary target of photodamage and environmental stress can accelerate this process. Cyanobacterial response to stress includes transcriptional regulation of genes encoding D1, including low‐oxygen‐induction of psbA1 encoding the D1´ protein in Synechocystis sp. PCC 6803. We found that a D1´‐PS II strain was outperformed by a D1‐PS II strain when centres were produced under aerobic conditions; however, a strain containing low‐oxygen‐induced D1´‐PS II centres was more resilient under high light than an equivalent D1 strain. Our results indicate that D1´‐PS II centres are important in the reconfiguration of thylakoid electron transport in response to high light and low oxygen.
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