Protein Phosphatase 2A in the Regulatory Network Underlying Biotic Stress Resistance in Plants

Biotic stress factors pose a major threat to plant health and can significantly deteriorate plant productivity by impairing the physiological functions of the plant. To combat the wide range of pathogens and insect herbivores, plants deploy converging signaling pathways, where counteracting activities of protein kinases and phosphatases form a basic mechanism for determining appropriate defensive measures. Recent studies have identified Protein Phosphatase 2A (PP2A) as a crucial component that controls pathogenesis responses in various plant species. Genetic, proteomic and metabolomic approaches have underscored the versatile nature of PP2A, which contributes to the regulation of receptor signaling, organellar signaling, gene expression, metabolic pathways, and cell death, all of which essentially impact plant immunity. Associated with this, various PP2A subunits mediate post-translational regulation of metabolic enzymes and signaling components. Here we provide an overview of protein kinase/phosphatase functions in plant immunity signaling, and position the multifaceted functions of PP2A in the tightly inter-connected regulatory network that controls the perception, signaling and responding to biotic stress agents in plants.Peer reviewe

De la compétence à l’empathie : évaluation de l’évolution de la perception qu’ont les étudiants en médecine des chirurgiens dans le cadre d’un programme associant le patient comme enseignant et la réflexion basée sur les arts

Introduction: The purpose of this study was to identify whether the incorporation of a combined Patient as teacher (PAT) and arts-based reflection (ABR) program during a surgical clerkship rotation could influence more humanistic perceptions of surgeons, using an innovative evaluation approach. Methods: A novel, single question evaluation tool was created. Third year medical-students were asked to “list the top 5 attributes of a surgeon, in order of perceived importance” both before and after their surgical clerkship rotations and participation in the PAT/ABR program. Attributes identified by students were coded as either “humanistic” or “non-humanistic,” which were then analyzed using generalized linear regression models under a Bayesian framework. Results: After participation in the PAT/ABR program, the predicted probability of students ranking a humanistic characteristic as the most important attribute of a surgeon had increased by 17%, and the predicted probability of students ranking a humanistic characteristic amongst their top three attributes for a surgeon had increased by 21%. Conclusion: This innovative evaluative method suggested the success of a combined PAT/ABR program in encouraging a humanistic perspective of surgery and this approach could potentially be explored to evaluate other humanistic education initiatives.Résumé Introduction : L’objectif de cette étude était de déterminer si l’introduction d’une nouvelle approche d’évaluation associant la participation de Patients comme enseignants (PCE) à une Réflexion basée sur les arts (RBA) dans un stage d’externat en chirurgie permettait de mieux percevoir les qualités humanistes chez les chirurgiens. Méthodes : Un nouvel outil d’évaluation à question unique a été créé. Des étudiants en troisième année de médecine ont été invités à ‘’énumérer les cinq principaux attributs d’un chirurgien, par ordre d’importance perçue’’, avant et après leur stage d’externat en chirurgie et le programme PCE/RBA. Les attributs identifiés par les étudiants ont été codés comme « humanistes » ou « non humanistes », puis analysés à l’aide de modèles de régression linéaire généralisée dans un cadre bayésien. Résultats : Après leur participation au programme PCE/RBA, la probabilité prédite moyenne que les étudiants classent un trait humaniste comme l’attribut le plus important d’un chirurgien a augmenté de 17 %, et la probabilité prédite que les étudiants classent un trait humaniste parmi les trois premiers attributs d’un chirurgien a augmenté de 21 %. Conclusion : Cette méthode d’évaluation innovante porte à croire que le programme PCE/RBA réussit en effet à favoriser une vision humaniste de la chirurgie. Cette approche peut être explorée pour évaluer d’autres activités de formation axées sur l’humanisme

Rapid Responses to Abiotic Stress : Priming the Landscape for the Signal Transduction Network

Plants grow and reproduce within a highly dynamic environment that can see abrupt changes in conditions, such as light intensity, temperature, humidity, or interactions with biotic agents. Recent studies revealed that plants can respond within seconds to some of these conditions, engaging many different metabolic and molecular networks, as well as rapidly altering their stomatal aperture. Some of these rapid responses were further shown to propagate throughout the entire plant via waves of reactive oxygen species (ROS) and Ca2+ that are possibly mediated through the plant vascular system. Here, we propose that the integration of these signals is mediated through pulses of gene expression that are coordinated throughout the plant in a systemic manner by the ROS/Ca+2 waves.Peer reviewe

“Disadvantaged patient populations”: A theory-informed education needs assessment in an urban teaching hospital

Recent calls in medical education and health care emphasize equitable care for disadvantaged patient populations (DPP), with education  highlighted as a key mechanism to move toward this goal. However, in order to develop effective education strategies we must first better understand the DPP concept. We conducted a theory-informed needs assessment to explore the concept of DPP as understood in our hospital.  Using an interpretive qualitative approach informed by principles of critical discourse analysis we conducted focus groups with trainees and staff across professions and groups, as identified in the hospital’s strategic plan, representing “patients experiencing disadvantage.” We identified three main perceptions about DPP:  1) disadvantaged patients require care above and beyond what is normal; 2) the system is to blame for failures in serving disadvantaged patients; and 3) labelling patients is problematic and stigmatizing. In response, patients wanted to be first seen as valuable human beings rather than as a burden or category. Patients appreciated that the DPP concept opened up better access to care, but also felt ‘othered’ by the concept. As a result, patients felt they were not accessing the same level of care in terms of compassion and respect.  Our findings suggest potential for three, theory-informed educational approaches to help improve care for patients experiencing disadvantage: 1) sharing authentic and varied stories; 2) fostering dialogue; and 3) aligning assessment approaches with educational approaches. Additionally, we suggest a need to define access beyond the ability to receive services; according to our participants, access must also engender a sense of common humanity and respect.&nbsp

Structural and biochemical characterization of the C3–C4 intermediate Brassica gravinae and relatives, with particular reference to cellular distribution of Rubisco

On the basis of its CO2 compensation concentration, Brassica gravinae Ten. has been reported to be a C3–C4 intermediate. This study investigated the structural and biochemical features of photosynthetic metabolism in B. gravinae. The cellular distribution of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) was also examined in B. gravinae, B. napus L. (C3), Raphanus sativus L. (C3), and Diplotaxis tenuifolia (L.) DC. (C3–C4) by immunogold electron microscopy to elucidate Rubisco expression during the evolution from C3 to C3–C4 intermediate plants. The bundle sheath (BS) cells of B. gravinae contained centrifugally located chloroplasts as well as centripetally located chloroplasts and mitochondria. Glycine decarboxylase P-protein was localized in the BS mitochondria. Brassica gravinae had low C4 enzyme activities and high activities of Rubisco and photorespiratory enzymes, suggesting that it reduces photorespiratory CO2 loss by the glycine shuttle. In B. gravinae, the labelling density of Rubisco was higher in the mesophyll chloroplasts than in the BS chloroplasts. A similar cellular pattern was found in other Brassicaceae species. These data demonstrate that, during the evolution from C3 to C3–C4 intermediate plants, the intercellular pattern of Rubisco expression did not change greatly, although the amount of chloroplasts in the BS cells increased. It also appears that intracellular variation in Rubisco distribution may occur within the BS cells of B. gravinae

Transcriptional regulation of the CRK/DUF26 group of Receptor-like protein kinases by ozone and plant hormones in Arabidopsis

Conclusions: Combining expression analysis from multiple treatments with mutants altered in hormone biosynthesis or signalling suggest a model in which O(3) and salicylic acid (SA) activate separate signaling pathways that exhibit negative crosstalk. Although O(3) is classified as an abiotic stress to plants, transcriptional profiling of CRKs showed strong similarities between the O(3) and biotic stress responses

Interaction of methyl viologen-induced chloroplast and mitochondrial signalling in Arabidopsis

Reactive oxygen species (ROS) are key signalling intermediates in plant metabolism, defence, and stress adaptation. In plants, both the chloroplast and mitochondria are centres of metabolic control and ROS production, which coordinate stress responses in other cell compartments. The herbicide and experimental tool, methyl viologen (MV) induces ROS generation in the chloroplast under illumination, but is also toxic in non-photosynthetic organisms. We used MV to probe plant ROS signalling in compartments other than the chloroplast. Taking a genetic approach in the model plant Arabidopsis (Arabidopsis thaliana), we used natural variation, QTL mapping, and mutant studies with MV in the light, but also under dark conditions, when the chloroplast electron transport is inactive. These studies revealed a light-independent MV-induced ROS-signalling pathway, suggesting mitochondrial involvement. Mitochondrial Mn SUPEROXIDE DISMUTASE was required for ROS-tolerance and the effect of MV was enhanced by exogenous sugar, providing further evidence for the role of mitochondria. Mutant and hormone feeding assays revealed roles for stress hormones in organellar ROS-responses. The radical-induced cell death1 mutant, which is tolerant to MV-induced ROS and exhibits altered mitochondrial signalling, was used to probe interactions between organelles. Our studies suggest that mitochondria are involved in the response to ROS induced by MV in plants.Peer reviewe

PP2A-B’γ modulates foliar trans-methylation capacity and the formation of 4-methoxy-indol-3-yl-methyl glucosinolate in Arabidopsis leaves

Glucosinolates (GSL) of cruciferous plants comprise a major group of structurally diverse secondary compounds which act as deterrents against aphids and microbial pathogens and have large commercial and ecological impacts. While the transcriptional regulation governing the biosynthesis and modification of GSL is now relatively well understood, post-translational regulatory components that specifically determine the structural variation of indole glucosinolates have not been reported. We show that the cytoplasmic protein phosphatase 2A regulatory subunit B'gamma (PP2A-B'gamma) physically interacts with indole glucosinolate methyltransferases and controls the methoxylation of indole glucosinolates and the formation of 4-meth-oxy-indol-3-yl-methyl glucosinolate in Arabidopsis leaves. By taking advantage of proteomic approaches and metabolic analysis we further demonstrate that PP2A-B'gamma is required to control the abundance of oligomeric protein complexes functionally linked with the activated methyl cycle and the trans-methylation capacity of leaf cells. These findings highlight the key regulatory role of PP2A-B'gamma in methionine metabolism and provide a previously unrecognized perspective for metabolic engineering of glucosinolate metabolism in cruciferous plants.Peer reviewe

Photosystem II Repair and Plant Immunity: Lessons Learned from Arabidopsis Mutant Lacking the THYLAKOID LUMEN PROTEIN 18.3

Chloroplasts play an important role in the cellular sensing of abiotic and biotic stress. Signals originating from photosynthetic light reactions, in the form of redox and pH changes, accumulation of reactive oxygen and electrophile species or stromal metabolites are of key importance in chloroplast retrograde signaling. These signals initiate plant acclimation responses to both abiotic and biotic stresses. To reveal the molecular responses activated by rapid fluctuations in growth light intensity, gene expression analysis was performed with Arabidopsis thaliana wild type and the tlp18.3 mutant plants, the latter showing a stunted growth phenotype under fluctuating light conditions (Biochem. J, 406, 415-425). Expression pattern of genes encoding components of the photosynthetic electron transfer chain did not differ between fluctuating and constant light conditions, neither in wild type nor in tlp18.3 plants, and the composition of the thylakoid membrane protein complexes likewise remained unchanged. Nevertheless, the fluctuating light conditions repressed in wild-type plants a broad spectrum of genes involved in immune responses, which likely resulted from shade-avoidance responses and their intermixing with hormonal signaling. On the contrary, in the tlp18.3 mutant plants there was an imperfect repression of defense-related transcripts upon growth under fluctuating light, possibly by signals originating from minor malfunction of the photosystem II (PSII) repair cycle, which directly or indirectly modulated the transcript abundances of genes related to light perception via phytochromes. Consequently, a strong allocation of resources to defense reactions in the tlp18.3 mutant plants presumably results in the stunted growth phenotype under fluctuating light.</p

Exposure to ozone reduces postharvest quality loss in red and green chilli peppers

The effect of continuous exposure to ozone at 0.45, 0.9 and 2 μmol mol−1 on quality changes during the storage of red and green chilli peppers at 10 °C was investigated. Ozone at 0.45 and 0.9 μmol mol−1 reduced disease incidence in red peppers, with no further benefits at 2 μmol mol−1. Ozone at 0.9 μmol mol−1 reduced weight loss during storage and improved firmness maintenance. Skin colour was bleached in red peppers exposed to ozone at 2 μmol mol−1, and in green ones at all tested doses. Total phenolic content was not affected by ozone but antioxidant activity was reduced in green chilli peppers exposed to ozone at 2 μmol mol−1, due to lower ascorbic acid content in those samples. Ozone at 0.9 μmol mol−1 extended the shelf-life of chilli peppers