BIG enhances Arg/N-degron pathway-mediated protein degradation to regulate Arabidopsis hypoxia responses and suberin deposition

BIG/DARK OVEREXPRESSION OF CAB1/TRANSPORT INHIBITOR RESPONSE3 is a 0.5-MDa protein associated with multiple functions in Arabidopsis (Arabidopsis thaliana) signalling and development. However, the biochemical functions of BIG are unknown. We investigated a role for BIG in the Arg/N-degron pathways, in which substrate protein fate is influenced by the N-terminal (Nt) residue. We crossed a big loss-of-function allele to two N-degron pathway E3 ligase mutants, proteolysis6 (prt6) and prt1, and examined the stability of protein substrates. Stability of model substrates was enhanced in prt6-1 big-2 and prt1-1 big-2 relative to the respective single mutants and the abundance of the PRT6 physiological substrates, HYPOXIA-RESPONSIVE ERF2 (HRE2) and VERNALIZATION2 (VRN2) was similarly increased in prt6 big double mutants. Hypoxia marker expression was enhanced in prt6 big double mutants; this constitutive response required arginyltransferase activity and RAP-type ERFVII transcription factors. Transcriptomic analysis of roots not only demonstrated increased expression of multiple hypoxia-responsive genes in the double mutant relative to prt6, but also revealed other roles for PRT6 and BIG, including regulation of suberin deposition through both ERFVII-dependent and independent mechanisms, respectively. Our results show that BIG acts together with PRT6 to regulate the hypoxia response and broader processes in Arabidopsis

Inter-species variation in the oligomeric states of the higher plant Calvin cycle enzymes glyceraldehyde-3-phosphate dehydrogenase and phosphoribulokinase

In darkened leaves the Calvin cycle enzymes glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and phosphoribulokinase (PRK) form a regulatory multi-enzyme complex with the small chloroplast protein CP12. GAPDH also forms a high molecular weight regulatory mono-enzyme complex. Given that there are different reports as to the number and subunit composition of these complexes and that enzyme regulatory mechanisms are known to vary between species, it was reasoned that protein-protein interactions may also vary between species. Here, this variation is investigated. This study shows that two different tetramers of GAPDH (an A2B2 heterotetramer and an A4 homotetramer) have the capacity to form part of the PRK/GAPDH/CP12 complex. The role of the PRK/GAPDH/CP12 complex is not simply to regulate the 'non-regulatory' A4 GAPDH tetramer. This study also demonstrates that the abundance and nature of PRK/GAPDH/CP12 interactions are not equal in all species and that whilst NAD enhances complex formation in some species, this is not sufficient for complex formation in others. Furthermore, it is shown that the GAPDH mono-enzyme complex is more abundant as a 2(A2B2) complex, rather than the larger 4(A2B2) complex. This smaller complex is sensitive to cellular metabolites indicating that it is an important regulatory isoform of GAPDH. This comparative study has highlighted considerable heterogeneity in PRK and GAPDH protein interactions between closely related species and the possible underlying physiological basis for this is discussed. © 2011 The Author(s)

Gene network analysis of Arabidopsis thaliana flower development through dynamic gene perturbations

Understanding how flowers develop from undifferentiated stem cells has occupied developmental biologists for decades. Key to unraveling this process is a detailed knowledge of the global regulatory hierarchies that control developmental transitions, cell differentiation and organ growth. These hierarchies may be deduced from gene perturbation experiments, which determine the effects on gene expression after specific disruption of a regulatory gene. Here, we tested experimental strategies for gene perturbation experiments during Arabidopsis thaliana flower development. We used artificial miRNAs (amiRNAs) to disrupt the functions of key floral regulators, and expressed them under the control of various inducible promoter systems that are widely used in the plant research community. To be able to perform genome‐wide experiments with stage‐specific resolution using the various inducible promoter systems for gene perturbation experiments, we also generated a series of floral induction systems that allow collection of hundreds of synchronized floral buds from a single plant. Based on our results, we propose strategies for performing dynamic gene perturbation experiments in flowers, and outline how they may be combined with versions of the floral induction system to dissect the gene regulatory network underlying flower development

Neither participation nor revolution: the strategy of the Moroccan Jamiat al-Adl wal-Ihsan

Scholars and students of Islamist movements are divided over the issue of Islamists' commitment to democracy and a number of studies have attempted to discover the true nature of Islamist parties. This paper rejects this approach and argues that the behaviour of Islamist parties can be better understood through an analysis of the constraints and opportunities that their surrounding environment provides. Specifically, the paper aims at explaining the choice of the Moroccan Jamiat al-Adl wal-Ihsan neither to participate in institutional politics nor to undertake violent actions to transform the regime. This is done through an examination of its relations with the other political actors. The paper argues that Jamiat al-Adl wal-Ihsan's behaviour is as much the product of rational thinking as it is of ideology and provides evidence to support this claim. Such findings are important not only in the Moroccan context, but contribute to a growing literature claiming that Islamist movements should be treated as rational political actors operating under 'environmental' constraints and opportunities

Mesure simultanée de la vitesse de phase, de l'atténuation des ondes ultrasonores, de l'épaisseur et de la masse volumique de matériaux composites

Under impact, the geometrical and mechanical properties of materials are modified. In composite materials, the damage is due to delamination between plies and macro-cracking appearance inside the matrix. These induce large modifications in velocity and attenuation of ultrasonic wave. Because thickness and density of the impacted material can also be influenced, we propose a simple ultrasonic method to measure these four properties in the same time. Plate thickness and wave velocity are deduced from the time of fly of several echoes, attenuation and density are obtained from a spectral analysis of these echoes. We test the method on three different materials : glass, PVC, glass/epoxy. The results obtained are quite good. In a further work, we will extend this method to focal probe, to increase spatial resolution

Cutting the line: manipulation of plant immunity by bacterial type III effector proteases

Pathogens and their hosts are engaged in an evolutionary arms race. Pathogen-derived effectors promote virulence by targeting components of a host’s innate immune system, while hosts have evolved proteins that sense effectors and trigger a pathogen-specific immune response. Many bacterial effectors are translocated into host cells using type III secretion systems. Type III effector proteases irreversibly modify host proteins by cleavage of peptide bonds and are prevalent among both plant and animal bacterial pathogens. In plants, the study of model effector proteases has yielded important insights into the virulence mechanisms employed by pathogens to overcome their host’s immune response, as well as into the mechanisms deployed by their hosts to detect these effector proteases and counteract their effects. In recent years, the study of a larger number of effector proteases, across a wider range of pathogens, has yielded novel insights into their functions and recognition. One key limitation that remains is the lack of methods to detect protease cleavage at the proteome-wide level. We review known substrates and mechanisms of plant pathogen type III effector proteases and compare their functions with those of known type III effector proteases of mammalian pathogens. Finally, we discuss approaches to uncover their function on a system-wide level

Factors influencing clinical consistency and variability in voice prosthesis management

Anecdotally it is recognised that management of tracheoesophageal speech (TES) post-laryngectomy varies between speech language pathology (SLP) services and clinicians. This study reviewed patterns of practice for TES management to examine patterns of practice and explore factors influencing variability.A national survey was completed by SLP's from clinical services which manage TES. This online survey examined demographic and caseload information, initial voice prosthesis (VP) placement and procedures, VP cleaning and care recommendations, humidification management, equipment and service provision, and service delivery options at each site.Lead clinicians from 34 sites (85% response rate) responded. Most clinical practice regarding initial VP insertion and management, as well as the timing and delivery of voice rehabilitation was highly consistent. Patient use of antifungal medications, TES and associated equipment provision, humidification management immediately post-surgery and some aspects of initial VP insertion were variable between services. The nature of the clinical setting, equipment funding and level of research evidence influenced variability in practice.Variability exists in a number of aspects of practice across Australian services offering TES management. Sources of variability need to be addressed nationally to ensure there is consistent, quality care available for all patients