RNAi-mediated suppression of isoprene emission in poplar transiently impacts phenolic metabolism under high temperature and high light intensities: a transcriptomic and metabolomic analysis

In plants, isoprene plays a dual role: (a) as thermo-protective agent proposed to prevent degradation of enzymes/membrane structures involved in photosynthesis, and (b) as reactive molecule reducing abiotic oxidative stress. The present work addresses the question whether suppression of isoprene emission interferes with genome wide transcription rates and metabolite fluxes in grey poplar (Populusxcanescens) throughout the growing season. Gene expression and metabolite profiles of isoprene emitting wild type plants and RNAi-mediated non-isoprene emitting poplars were compared by using poplar Affymetrix microarrays and non-targeted FT-ICR-MS (Fourier transform ion cyclotron resonance mass spectrometry). We observed a transcriptional down-regulation of genes encoding enzymes of phenylpropanoid regulatory and biosynthetic pathways, as well as distinct metabolic down-regulation of condensed tannins and anthocyanins, in non-isoprene emitting genotypes during July, when high temperature and light intensities possibly caused transient drought stress, as indicated by stomatal closure. Under these conditions leaves of non-isoprene emitting plants accumulated hydrogen peroxide (H2O2), a signaling molecule in stress response and negative regulator of anthocyanin biosynthesis. The absence of isoprene emission under high temperature and light stress resulted transiently in a new chemo(pheno)type with suppressed production of phenolic compounds. This may compromise inducible defenses and may render non-isoprene emitting poplars more susceptible to environmental stress

ROS-dependent signaling pathways in plants and algae exposed to high light: Comparisons with other eukaryotes

Abstract Like all aerobic organisms, plants and algae co-opt reactive oxygen species (ROS) as signaling molecules to drive cellular responses to changes in their environment. In this respect, there is considerable commonality between all eukaryotes imposed by the constraints of ROS chemistry, similar metabolism in many subcellular compartments, the requirement for a high degree of signal specificity and the deployment of thiol peroxidases as transducers of oxidizing equivalents to regulatory proteins. Nevertheless, plants and algae carry out specialised signaling arising from oxygenic photosynthesis in chloroplasts and photoautotropism, which often induce an imbalance between absorption of light energy and the capacity to use it productively. A key means of responding to this imbalance is through communication of chloroplasts with the nucleus to adjust cellular metabolism. Two ROS, singlet oxygen (1O2) and hydrogen peroxide (H2O2), initiate distinct signaling pathways when photosynthesis is perturbed. 1O2, because of its potent reactivity means that it initiates but does not transduce signaling. In contrast, the lower reactivity of H2O2 means that it can also be a mobile messenger in a spatially-defined signaling pathway. How plants translate a H2O2 message to bring about changes in gene expression is unknown and therefore, we draw on information from other eukaryotes to propose a working hypothesis. The role of these ROS generated in other subcellular compartments of plant cells in response to HL is critically considered alongside other eukaryotes. Finally, the responses of animal cells to oxidative stress upon high irradiance exposure is considered for new comparisons between plant and animal cells

Recommendations for the registration of agents to be used in the prevention and treatment of glucocorticoid-induced osteoporosis: updated recommendations from the Group for the Respect of Ethics and Excellence in Science.

OBJECTIVES: The Group for the Respect and Excellence in Science (GREES) has reviewed and updated their recommendations for clinical trials to evaluate the efficacy and safety of new chemical entities to be used in the treatment and prevention of glucocorticoid-induced osteoporosis (GIOP). METHODS: Consensus discussion of the committee. RESULTS: With the exception of steroid use posttransplantation, there is no need to differentiate between underlying diseases. Prevention and treatment for GIOP are dependent on exposure to glucocorticoids rather than T-scores as in postmenopausal osteoporosis (PMO). If fracture data are obtained for PMO, it need not be repeated for GIOP, relying instead on bone mineral density (BMD) trials of at least 1 year. GREES recommends several changes in the previous guidance for GIOP. The committee saw no need to repeat preclinical studies if those have been previously done to assure bone quality in PMO. Similarly, phase I and phase II trials, if careful dose selection has been done for PMO, should not be repeated. The "prevention" and "treatment" claims should remain. Since the most recent evidence suggests significant increase in fracture risk for daily doses of prednisone of 5 mg/day or equivalent, clinical trials should concentrate on patients receiving at least this daily dosage. The emergence of bisphosphonates as the reference treatment, together with the rapid bone loss and high fracture incidence in glucocorticoid users, necessitates recommending a noninferiority trial design with lumbar spine BMD as the primary endpoint after 1 year. CONCLUSIONS: Registration of new chemical entities to be used in the management of GIOP should be granted, based on a 1-year noninferiority trial, using BMD as primary outcome and alendronate or risedronate as comparator. Demonstration of antifracture efficacy should have been previously demonstrated in PMO