Spatial and temporal regulation of the forisome gene <Emphasis Type="Italic">for1</Emphasis> in the phloem during plant development

Forisomes are protein aggregates found uniquely in the sieve elements of Fabaceaen plants. Upon wounding they undergo a reversible, calcium-dependent conformational switch which enables them to act as cellular stopcocks. Forisomes begin to form in young sieve elements at an early stage of metaphloem differentiation. Genes encoding forisome components could therefore be useful as markers of early sieve element development. Here we present a comprehensive analysis of the developmental expression profile of for1, which encodes such a forisome component. The for1 gene is highly conserved among Fabaceaen species and appears to be unique to this phylogenetic lineage since no orthologous genes have been found in other plants, including Arabidopsis and rice. Even so, transgenic tobacco plants expressing reporter genes under the control of the for1 promoter display reporter activity exclusively in immature sieve elements. This suggests that the regulation of sieve element development is highly conserved even in plants where mature forisomes have not been detected. The promoter system could therefore provide a powerful tool for the detailed analysis of differentiation in metaphloem sieve elements in an unexpectedly broad range of plant species. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Gas chromatographic-mass spectroscopic identification and quantification of cyclic guanosine-3′: 5′-monophosphate in maize seedlings (Zea mays)

Gas chromatographic-mass spectroscopic evidence is presented for the presence of guanosine-3′: 5′-monophosphate (cGMP) in maize seedlings. The amount of cGMP (35–72 pmol g^-1 fresh weight) was quantified as a tetra-silyl derivative using gas-chromatographic detection with reference to a silylated standard of authentic cGMP. Gas-chromatographic separation of tri-silyl adenosine-3′: 5′-monophosphate and tetra-silyl cGMP is demonstrated.     

Agent-Based Mapping of Credit Risk for Sustainable Microfinance

By drawing analogies with independent research areas, we propose an unorthodox framework for mapping microfinance credit risk---a major obstacle to the sustainability of lenders outreaching to the poor. Specifically, using the elements of network theory, we constructed an agent-based model that obeys the stylized rules of microfinance industry. We found that in a deteriorating economic environment confounded with adverse selection, a form of latent moral hazard may cause a regime shift from a high to a low loan payment probability. An after-the-fact recovery, when possible, required the economic environment to improve beyond that which led to the shift in the first place. These findings suggest a small set of measurable quantities for mapping microfinance credit risk and, consequently, for balancing the requirements to reasonably price loans and to operate on a fully self-financed basis. We illustrate how the proposed mapping works using a 10-year monthly data set from one of the best-known microfinance representatives, Grameen Bank in Bangladesh. Finally, we discuss an entirely new perspective for managing microfinance credit risk based on enticing spontaneous cooperation by building social capital.     

Inferring dynamic architecture of cellular networks using time series of gene expression, protein and metabolite data

MOTIVATION: High-throughput technologies have facilitated the acquisition of large genomics and proteomics datasets. However, these data provide snapshots of cellular behavior, rather than help us reveal causal relations. Here, we propose how these technologies can be utilized to infer the topology and strengths of connections among genes, proteins and metabolites by monitoring time-dependent responses of cellular networks to experimental interventions. RESULTS: We demonstrate that all connections leading to a given network node, e.g. to a particular gene, can be deduced from responses to perturbations none of which directly influences that node, e.g. using strains with knock-outs to other genes. To infer all interactions from stationary data, each node should be perturbed separately or in combination with other nodes. Monitoring time series provides richer information and does not require perturbations to all nodes. Overall, the methods we propose are capable of deducing and quantifying functional interactions within and across cellular gene, signaling and metabolic networks. SUPPLEMENTARY INFORMATION: Supplementary material is available at http://www.dbi.tju.edu/bioinformatics2004.pdf     

Angiomotin belongs to a novel protein family with conserved coiled-coil and PDZ binding domains

Angiomotin has previously been identified in a yeast two-hybrid screen by its ability to bind to angiostatin, an inhibitor of novel formation of blood vessels (angiogenesis). Angiomotin mediates the inhibitory effect of angiostatin on endothelial cell migration and tube formation in vitro. Here we report that two human protein sequences, of which one is novel and one has been cloned previously, are similar to angiomotin and are members of a novel protein family, which we propose to call motins. These two genes have been named angiomotin-like 1 (amotl1) and angiomotin-like 2 (amotl2). We have cloned mouse angiomotin and identified amotl1 and amotl2 homologs in mice. The alignment of the amino acid sequences encoded by these six sequences spans 455 residues of which 64% was conserved in all six proteins. Sequence analysis showed that these sequences all share putative coiled-coil domains and PDZ-binding motifs. Sequence information from GenBank indicate that motins can be found in several species including the frog Xenopus laevis, the pufferfish Fugu rubripes and the nematode Caenorhabditis elegans. Further phylogenetic analysis indicates that amotl2 is an evolutionary outgroup in relation to angiomotin and amotl1. Northern blot analysis shows distinct expression patterns for each motin in various mouse tissues.     

Interaction of ascorbate with photosystem I

Ascorbate is one of the key participants of the antioxidant defense in plants. In this work, we have investigated the interaction of ascorbate with the chloroplast electron transport chain and isolated photosystem I (PSI), using the EPR method for monitoring the oxidized centers \( {\text{P}}_{700}^{ + } \) and ascorbate free radicals. Inhibitor analysis of the light-induced redox transients of P₇₀₀ in spinach thylakoids has demonstrated that ascorbate efficiently donates electrons to \( {\text{P}}_{ 7 0 0}^{ + } \) via plastocyanin. Inhibitors (DCMU and stigmatellin), which block electron transport between photosystem II and Pc, did not disturb the ascorbate capacity for electron donation to \( {\text{P}}_{700}^{ + } \) . Otherwise, inactivation of Pc with CN^? ions inhibited electron flow from ascorbate to \( {\text{P}}_{700}^{ + } \) . This proves that the main route of electron flow from ascorbate to \( {\text{P}}_{700}^{ + } \) runs through Pc, bypassing the plastoquinone (PQ) pool and the cytochrome b ₆ f complex. In contrast to Pc-mediated pathway, direct donation of electrons from ascorbate to \( {\text{P}}_{700}^{ + } \) is a rather slow process. Oxidized ascorbate species act as alternative oxidants for PSI, which intercept electrons directly from the terminal electron acceptors of PSI, thereby stimulating photooxidation of P₇₀₀. We investigated the interaction of ascorbate with PSI complexes isolated from the wild type cells and the MenB deletion strain of cyanobacterium Synechocystis sp. PCC 6803. In the MenB mutant, PSI contains PQ in the quinone-binding A₁-site, which can be substituted by high-potential electron carrier 2,3-dichloro-1,4-naphthoquinone (Cl₂NQ). In PSI from the MenB mutant with Cl₂NQ in the A₁-site, the outflow of electrons from PSI is impeded due to the uphill electron transfer from A₁ to the iron-sulfur cluster F_X and further to the terminal clusters F_A/F_B, which manifests itself as a decrease in a steady-state level of \( {\text{P}}_{700}^{ + } \) . The addition of ascorbate promoted photooxidation of P₇₀₀ due to stimulation of electron outflow from PSI to oxidized ascorbate species. Thus, accepting electrons from PSI and donating them to \( {\text{P}}_{700}^{ + } \) , ascorbate can mediate cyclic electron transport around PSI. The physiological significance of ascorbate-mediated electron transport is discussed.     

Crh, the paralogue of the phosphocarrier protein HPr, controls the methylglyoxal bypass of glycolysis in Bacillus subtilis

The histidine protein HPr has a key role in regulation of carbohydrate utilization in low-GC Gram-positive bacteria. Bacilli possess the paralogue Crh. Like HPr, Crh becomes phosphorylated by kinase HPrK/P in response to high fructose-1,6-bisphosphate concentrations. However, Crh can only partially substitute for the regulatory functions of HPr leaving its role mysterious. Using protein co-purification, we identified enzyme methylglyoxal synthase MgsA as interaction partner of Crh in Bacillus subtilis. MgsA converts dihydroxyacetone-phosphate to methylglyoxal and thereby initiates a glycolytic bypass that prevents the deleterious accumulation of phospho-sugars under carbon overflow conditions. However, methylgyloxal is toxic and its production requires control. We show here that exclusively the non-phosphorylated form of Crh interacts with MgsA in vivo and inhibits MgsA activity in vitro. Accordingly, Crh inhibits methylglyoxal formation in vivo under nutritional famine conditions that favour a low HPr kinase activity. Thus, Crh senses the metabolic state of the cell, as reflected by its phosphorylation state, and accordingly controls flux through the harmful methylglyoxal pathway. Interestingly, HPr is unable to bind and regulate MgsA, making this a bona fide function of Crh. Four residues that differ in the interaction surfaces of HPr and Crh may account for this difference.