Low temperature is a primary determinant of plant growth and survival. Using accessions of Arabidopsis (Arabidopsis thaliana) originating from Scandinavia to the Cape Verde Islands, we show that freezing tolerance of natural accessions correlates with habitat winter temperatures, identifying low temperature as an important selective pressure for Arabidopsis. Combined metabolite and transcript profiling show that during cold exposure, global changes of transcripts, but not of metabolites, correlate with the ability of Arabidopsis to cold acclimate. There are, however, metabolites and transcripts, including several transcription factors, that correlate with freezing tolerance, indicating regulatory pathways that may be of primary importance for this trait. These data identify that enhanced freezing tolerance is associated with the down-regulation of photosynthesis and hormonal responses and the induction of flavonoid metabolism, provide evidence for naturally increased nonacclimated freezing tolerance due to the constitutive activation of the C-repeat binding factors pathway, and identify candidate transcriptional regulators that correlate with freezing tolerance.

An array of 2,304 cDNA clones derived from nitrogen-fixing nodules of Lotus japonicus was produced and used to detect differences in relative gene transcript abundance between nodules and uninfected roots. Transcripts of 83 different genes were found to be more abundant in nodules than in roots. More than 50 of these have never before been identified as nodule-induced in any species. Expression of 36 genes was detected in nodules but not in roots. Several known nodulin genes were included among the nodule-induced genes. Also included were genes involved in sucrose breakdown and glycolysis, CO2 recycling, and amino acid synthesis, processes that are known to be accelerated in nodules compared with roots. Genes involved in membrane transport, hormone metabolism, cell wall and protein synthesis, and signal transduction and regulation of transcription were also induced in nodules. Genes that may subvert normal plant defense responses, including two encoding enzymes involved in detoxification of active oxygen species and one that may prohibit phytoalexin synthesis, were also identified. The data represent a rich source of information for hypothesis building and future exploration of symbiotic nitrogen fixation.

Poster Sessions C217 spacer-and RPEL-actins, which bind weakly in solution. Cytoplasmic MRTF-A localization in resting fibroblasts requires spacer-actin binding. The bipartite importin {alpha-beta} binding site is buried in the pentameric assembly, explaining how elevated G-actin concentrations prevent MRTF-A nuclear import. The structures show how actin loads onto the RPEL domain, and reveal a molecular mechanism by which actin can control the activity of one of its ligands. The diazotrophic soil bacterium Azotobacter vinelandii utilizes a FeMo-cofactor containing nitrogenase to accomplish nitrogen fixation. As nitrogenase is required in large amounts, the cell extracts a lot of molybdenum (Mo) from the environment and stores it in a special Molybdenum Storage Protein (MoSto)[1] as polyoxometalate clusters [2]. MoSto crystallizes in a needle-like shape. Best crystals diffract to 1.6Å resolution. An X-ray crystal analysis of the Mo-loaded MoSto revealed different types of Mo-oxide based clusters some being covalently bound while others are not. These clusters are synthesized in an ATP-dependent process whose mechanism is not yet known. Invitro experiments showed that it is possible to entirely deplete MoSto from its metal clusters and subsequently reload it again. The depletion is a pH-driven triphasic process which can be varied with temperature and time of incubation [1]. MoSto can load up to 120 atoms per protein molecule. Further research is necessary to determine the mechanism how the clusters are built from monomolybdates and how their selective release from MoSto is organized.[1] J. Schemberg et al., ChemBioChem 2008, 9, 595-602 DivIVA is a highly conserved protein in Gram-positive bacteria that localizes at the poles and division sites, presumably through direct sensing of membrane curvature. The correct localization of the protein is essential for its biological function, which involve both the correct placement of the septum at midcell and also the segregation of the DNA into the pre-spore during sporulation. DivIVA deletion causes filamentous growth in Bacillus subtilis, whereas overexpression causes hyphal branching in Streptomyces coelicolor. The mechanism of subcellular DivIVA targeting and function remain unknown. We present data that demonstrates that DivIVA binds directly to bacteria membrane and explains how this protein shows a multifunctional behavior.We prove that DivIVA is a two independent domains protein linked by a flexible tag and both domains together are essential to fulfill protein localization and function. The crystal structure determination shows that both domains share a parallel coiled-coil folding. Surprisingly the N-terminal domain also includes crossed and intertwined loops between the two coiled-coil molecules, which is completely new and is involved in protein targeting in combination with the presence of a key hydrophobic residue surrounded by positively charged residues. To clarify N-terminal domain function in DivIVA membrane targeting we have used an in vivo and in vitr...

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