The effects of physiologically plausible connectivity structure on local and global dynamics in large scale brain models.

Functionally relevant large scale brain dynamics operates within the framework imposed by anatomical connectivity and time delays due to finite transmission speeds. To gain insight on the reliability and comparability of large scale brain network simulations, we investigate the effects of variations in the anatomical connectivity. Two different sets of detailed global connectivity structures are explored, the first extracted from the CoCoMac database and rescaled to the spatial extent of the human brain, the second derived from white-matter tractography applied to diffusion spectrum imaging (DSI) for a human subject. We use the combination of graph theoretical measures of the connection matrices and numerical simulations to explicate the importance of both connectivity strength and delays in shaping dynamic behaviour. Our results demonstrate that the brain dynamics derived from the CoCoMac database are more complex and biologically more realistic than the one based on the DSI database. We propose that the reason for this difference is the absence of directed weights in the DSI connectivity matrix.

Emergence of secretion-defective sublines of Pseudomonas aeruginosa PAO1 resulting from spontaneous mutations in the vfr global regulatory gene.

Pseudomonas aeruginosa undergoes spontaneous mutation that impairs secretion of several extracellular enzymes during extended cultivation in vitro in rich media, as well as during long-term colonization of the cystic fibrosis lung. A frequent type of strong secretion deficiency is caused by inactivation of the quorum-sensing regulatory gene lasR. Here we analyzed a spontaneously emerging subline of strain PAO1 that exhibited moderate secretion deficiency and partial loss of quorum-sensing control. Using generalized transduction, we mapped the secretion defect to the vfr gene, which is known to control positively the expression of the lasR gene and type II secretion of several proteases. We confirmed this secretion defect by sequencing and complementation of the vfr mutation. In a reconstruction experiment conducted with a 1:1 mixture of wild-type strain PAO1 and a vfr mutant of PAO1, we observed that the vfr mutant had a selective advantage over the wild type after growth in static culture for 4 days. Under these conditions, spontaneous vfr emerged in a strain PAO1 population after four growth cycles, and these mutants accounted for more than 40% of the population after seven cycles. These results suggest that partial or complete loss of quorum sensing and secretion can be beneficial to P. aeruginosa under certain environmental conditions.

The global regulator GacA of Pseudomonas fluorescens CHA0 is required for the suppression of root diseases in dicotyledons but not in Gramineae

Pseudomonas fluorescens strain CHA0 suppresses various plant diseases caused by soil-borne fungi. The pseudomonad produces the antimicrobial metabolites 2,4-diacetylphloroglucinol (Phl), pyoluteorin (Plt) and hydrogen cyanide, which are important for disease suppression, as well as the siderophores pyoverdine (Pvd), salicylic acid (Sal) and pyochelin (Pch). In the current work, a derivative of CHA0 with a mutation in the global regulator gene gacA (GacA−), which is unable to produce Phl, Plt and HCN, failed to protect the dicotyledonous plants cress and cucumber against damping-off caused by Pythium ultimum. In contrast, the GacA− mutant could still protect the Gramineae wheat and maize against damping-off mediated by the same strain of P. ultimum, and wheat against take-all caused by Gaeumannomyces graminis. However, the GacA− mutant overproduced Pch and Pvd. To gain more insight into disease protection afforded by the GacA− mutant, a GacA− Pvd− double mutant (strain CHA496) was constructed by gene replacement. Strain CHA496 overproduced Pch and Sal compared with CHA0 and protected wheat against P. ultimum and G. graminis, whereas cress and cucumber were not protected. Addition of FeCl3 repressed Pch and Sal production by strain CHA496 in vitro and impaired the protection of wheat in soil microcosms. In conclusion, a functional gacA gene was necessary for the protection of dicotyledons against root diseases, but not for that of Gramineae. Results indicated also that Pch and/or Sal were involved in the ability of the GacA− Pvd− mutant of CHA0 to suppress root diseases in Gramineae.

Arabidopsis lox3 lox4 double mutants are male sterile and defective in global proliferative arrest.

Fertility and flower development are both controlled in part by jasmonates, fatty acid-derived mediators produced via the activity of 13-lipoxygenases (13-LOXs). The Arabidopsis thaliana Columbia-0 reference genome is predicted to encode four of these enzymes and it is already known that one of these, LOX2, is dispensable for fertility. In this study, the roles of the other three 13-LOXs (LOX3, LOX4 and LOX6) were investigated in single and double mutants. Four independent lox3 lox4 double mutants assembled with different mutated lox3 and lox4 alleles had fully penetrant floral phenotypes, displaying abnormal anther maturation and defective dehiscence. The plants were no longer self-fertile and pollen was not viable. Fertility in the double mutant was restored genetically by complementation with either the LOX3 or the LOX4 cDNAs and biochemically with exogenous jasmonic acid. Furthermore, deficiency in LOX3 and LOX4 causes developmental dysfunctions, compared to wild type; lox3 lox4 double mutants are taller and develop more inflorescence shoots and flowers. Further analysis revealed that developmental arrest in the lox3 lox4 inflorescence occurs with the production of an abnormal carpelloid flower. This distinguishes lox3 lox4 mutants from the wild type where developmentally typical flower buds are the terminal inflorescence structures observed in both the laboratory and in nature. Our studies of lox3 lox4 as well as other jasmonic acid biosynthesis and perception mutants show that this plant hormone is not only required for male fertility but also involved in global proliferative arrest.

Small Cities, Neoliberal Governance and Sustainable Development in the Global South : A Conceptual Framework and Research Agenda

Development and environmental issues of small cities in developing countries have largely been overlooked although these settlements are of global demographic importance and often face a "triple challenge"; that is, they have limited financial and human resources to address growing environmental problems that are related to both development (e.g., pollution) and under-development (e.g., inadequate water supply). Neoliberal policy has arguably aggravated this challenge as public investments in infrastructure generally declined while the focus shifted to the metropolitan "economic growth machines". This paper develops a conceptual framework and agenda for the study of small cities in the global south, their environmental dynamics, governance and politics in the current neoliberal context. While small cities are governed in a neoliberal policy context, they are not central to neoliberalism, and their (environmental) governance therefore seems to differ from that of global cities. Furthermore, "actually existing" neoliberal governance of small cities is shaped by the interplay of regional and local politics and environmental situations. The approach of urban political ecology and the concept of rural-urban linkages are used to consider these socio-ecological processes. The conceptual framework and research agenda are illustrated in the case of India, where the agency of small cities in regard to environmental governance seems to remain limited despite formal political decentralization.