An Intergenic Region Shared by At4g35985 and At4g35987 in Arabidopsis Thaliana is a Tissue Specific and Stress Inducible Bidirectional Promoter Analyzed in Transgenic Arabidopsis and Tobacco Plants

On chromosome 4 in the Arabidopsis genome, two neighboring genes (calmodulin methyl transferase At4g35987 and senescence associated gene At4g35985) are located in a head-to-head divergent orientation sharing a putative bidirectional promoter. This 1258 bp intergenic region contains a number of environmental stress responsive and tissue specific cis-regulatory elements. Transcript analysis of At4g35985 and At4g35987 genes by quantitative real time PCR showed tissue specific and stress inducible expression profiles. We tested the bidirectional promoter-function of the intergenic region shared by the divergent genes At4g35985 and At4g35987 using two reporter genes (GFP and GUS) in both orientations in transient tobacco protoplast and Agro-infiltration assays, as well as in stably transformed transgenic Arabidopsis and tobacco plants. In transient assays with GFP and GUS reporter genes the At4g35985 promoter (P85) showed stronger expression (about 3.5 fold) compared to the At4g35987 promoter (P87). The tissue specific as well as stress responsive functional nature of the bidirectional promoter was evaluated in independent transgenic Arabidopsis and tobacco lines. Expression of P85 activity was detected in the midrib of leaves, leaf trichomes, apical meristemic regions, throughout the root, lateral roots and flowers. The expression of P87 was observed in leaf-tip, hydathodes, apical meristem, root tips, emerging lateral root tips, root stele region and in floral tissues. The bidirectional promoter in both orientations shows differential up-regulation (2.5 to 3 fold) under salt stress. Use of such regulatory elements of bidirectional promoters showing spatial and stress inducible promoter-functions in heterologous system might be an important tool for plant biotechnology and gene stacking applications

Catalytic hydrogenation of CO2 to formates by a lutidine-derived Ru-CNC pincer complex : Theoretical insight into the unrealized potential

Metal-ligand cooperative properties of a bis-N-heterocyclic carbene ruthenium CNC pincer catalyst and its activity in CO2 hydrogenation to formates were studied by DFT calculations complemented by NMR spectroscopy and kinetic measurements. The dearomatized Ru-CNC∗ pincer (1∗) is significantly more reactive toward metal-ligand cooperative activation of H2 and CO2 than the structurally related phosphine-based Ru-PNP complex. The enhanced reactivity of Ru-CNC∗ stems from the combination of electronic properties of this system and the reduced geometric constraints imposed onto the Ru center by the large and flexible CNC chelate. Heterolytic dissociation of H2 by 1∗ results in the bis-hydrido complex 2 that is active in hydrogenation of CO2. However, under commonly applied reaction conditions, the catalyst rapidly deactivates via metal-ligand cooperative paths. The transient formation of the dearomatized complex Ru-CNC∗ (1∗) in the course of the reaction leads to the irreversible cooperative activation of CO2, resulting in the stable adduct 3 that is not catalytically competent. By an increase in the H2/CO2 ratio, this deactivation path can be effectively suppressed, resulting in a stable and rather high catalytic performance of Ru-CNC. (Chemical Equation Presented)

Catalytic Hydrogenation of CO₂ to Formates by a Lutidine-Derived Ru–CNC Pincer Complex: Theoretical Insight into the Unrealized Potential

Metal–ligand cooperative properties of a bis-N-heterocyclic carbene ruthenium CNC pincer catalyst and its activity in CO₂ hydrogenation to formates were studied by DFT calculations complemented by NMR spectroscopy and kinetic measurements. The dearomatized Ru–CNC* pincer (<b>1*</b>) is significantly more reactive toward metal–ligand cooperative activation of H₂ and CO₂ than the structurally related phosphine-based Ru–PNP complex. The enhanced reactivity of Ru–CNC* stems from the combination of electronic properties of this system and the reduced geometric constraints imposed onto the Ru center by the large and flexible CNC chelate. Heterolytic dissociation of H₂ by <b>1*</b> results in the bis-hydrido complex <b>2</b> that is active in hydrogenation of CO₂. However, under commonly applied reaction conditions, the catalyst rapidly deactivates via metal–ligand cooperative paths. The transient formation of the dearomatized complex Ru–CNC* (<b>1*</b>) in the course of the reaction leads to the irreversible cooperative activation of CO₂, resulting in the stable adduct <b>3</b> that is not catalytically competent. By an increase in the H₂/CO₂ ratio, this deactivation path can be effectively suppressed, resulting in a stable and rather high catalytic performance of Ru–CNC

Transcriptional analyses of natural leaf senescence in maize.

Leaf senescence is an important biological process that contributes to grain yield in crops. To study the molecular mechanisms underlying natural leaf senescence, we harvested three different developmental ear leaves of maize, mature leaves (ML), early senescent leaves (ESL), and later senescent leaves (LSL), and analyzed transcriptional changes using RNA-sequencing. Three sets of data, ESL vs. ML, LSL vs. ML, and LSL vs. ESL, were compared, respectively. In total, 4,552 genes were identified as differentially expressed. Functional classification placed these genes into 18 categories including protein metabolism, transporters, and signal transduction. At the early stage of leaf senescence, genes involved in aromatic amino acids (AAAs) biosynthetic process and transport, cellular polysaccharide biosynthetic process, and the cell wall macromolecule catabolic process, were up-regulated. Whereas, genes involved in amino acid metabolism, transport, apoptosis, and response to stimulus were up-regulated at the late stage of leaf senescence. Further analyses reveals that the transport-related genes at the early stage of leaf senescence potentially take part in enzyme and amino acid transport and the genes upregulated at the late stage are involved in sugar transport, indicating nutrient recycling mainly takes place at the late stage of leaf senescence. Comparison between the data of natural leaf senescence in this study and previously reported data for Arabidopsis implies that the mechanisms of leaf senescence in maize are basically similar to those in Arabidopsis. A comparison of natural and induced leaf senescence in maize was performed. Athough many basic biological processes involved in senescence occur in both types of leaf senescence, 78.07% of differentially expressed genes in natural leaf senescence were not identifiable in induced leaf senescence, suggesting that differences in gene regulatory network may exist between these two leaf senescence programs. Thus, this study provides important information for understanding the mechanism of leaf senescence in maize