Global plant trait relationships extend to the climatic extremes of the tundra biome.

The majority of variation in six traits critical to the growth, survival and reproduction of plant species is thought to be organised along just two dimensions, corresponding to strategies of plant size and resource acquisition. However, it is unknown whether global plant trait relationships extend to climatic extremes, and if these interspecific relationships are confounded by trait variation within species. We test whether trait relationships extend to the cold extremes of life on Earth using the largest database of tundra plant traits yet compiled. We show that tundra plants demonstrate remarkably similar resource economic traits, but not size traits, compared to global distributions, and exhibit the same two dimensions of trait variation. Three quarters of trait variation occurs among species, mirroring global estimates of interspecific trait variation. Plant trait relationships are thus generalizable to the edge of global trait-space, informing prediction of plant community change in a warming world.

MP1: a MEK binding partner that enhances enzymatic activation of the MAP kinase cascade.

Signal transduction is controlled both by regulation of enzyme activation and by organization of enzymatic complexes with nonenzymatic adapters, scaffolds, and anchor proteins. The extracellular signal-regulated kinase (ERK) cascade is one of several evolutionarily conserved mitogen-activated protein (MAP) kinase cascades important in the regulation of growth, apoptosis, and differentiation. A two-hybrid screen was conducted to identify nonenzymatic components of this signaling cascade that might be important in regulating its activity. A protein called MP1 (MEK Partner 1) was identified that bound specifically to MEK1 and ERK1 and facilitated their activation. When overexpressed in cultured cells, MP1 enhanced activation of ERK1 and activation of a reporter driven by the transcription factor Elk-1. Expression of MP1 in cells increased binding of ERK1 to MEK1. MP1 apparently functions as an adapter to enhance the efficiency of the MAP kinase cascade.

benK encodes a hydrophobic permease-like protein involved in benzoate degradation by Acinetobacter sp. strain ADP1.

The chromosomal benK gene was identified within a supraoperonic gene cluster involved in benzoate degradation by Acinetobacter sp. strain ADP1, and benK was expressed in response to a benzoate metabolite, cis,cis-muconate. The disruption of benK reduced benzoate uptake and impaired the use of benzoate or benzaldehyde as the carbon source. BenK was homologous to several aromatic compound transporters.

Regulation of benzoate degradation in Acinetobacter sp. strain ADP1 by BenM, a LysR-type transcriptional activator.

In Acinetobacter sp. strain ADP1, benzoate degradation requires the ben genes for converting benzoate to catechol and the cat genes for degrading catechol. Here we describe a novel transcriptional activator, BenM, that regulates the chromosomal ben and cat genes. BenM is homologous to CatM, a LysR-type transcriptional activator of the cat genes. Unusual regulatory features of this system include the abilities of both BenM and CatM to recognize the same inducer, cis,cis-muconate, and to regulate some of the same genes, such as catA and catB. Unlike CatM, BenM responded to benzoate. Benzoate together with cis,cis-muconate increased the BenM-dependent expression of the benABCDE operon synergistically. CatM was not required for this synergism, nor did CatM regulate the expression of a chromosomal benA::lacZ transcriptional fusion. BenM-mediated regulation differs significantly from that of the TOL plasmid-encoded conversion of benzoate to catechol in pseudomonads. The benM gene is immediately upstream of, and divergently transcribed from, benA, and a possible DNA binding site for BenM was identified between the two coding regions. Two mutations in the predicted operator/promoter region rendered ben gene expression either constitutive or inducible by cis,cis-muconate but not benzoate. Mutants lacking BenM, CatM, or both of these regulators degraded aromatic compounds at different rates, and the levels of intermediary metabolites that accumulated depended on the genetic background. These studies indicated that BenM is necessary for ben gene expression but not for expression of the cat genes, which can be regulated by CatM. In a catM-disrupted strain, BenM was able to induce higher levels of catA expression than catB expression.

Key aromatic-ring-cleaving enzyme, protocatechuate 3,4-dioxygenase, in the ecologically important marine Roseobacter lineage.

Aromatic compound degradation in six bacteria representing an ecologically important marine taxon of the alpha-proteobacteria was investigated. Initial screens suggested that isolates in the Roseobacter lineage can degrade aromatic compounds via the beta-ketoadipate pathway, a catabolic route that has been well characterized in soil microbes. Six Roseobacter isolates were screened for the presence of protocatechuate 3,4-dioxygenase, a key enzyme in the beta-ketoadipate pathway. All six isolates were capable of growth on at least three of the eight aromatic monomers presented (anthranilate, benzoate, p-hydroxybenzoate, salicylate, vanillate, ferulate, protocatechuate, and coumarate). Four of the Roseobacter group isolates had inducible protocatechuate 3, 4-dioxygenase activity in cell extracts when grown on p-hydroxybenzoate. The pcaGH genes encoding this ring cleavage enzyme were cloned and sequenced from two isolates, Sagittula stellata E-37 and isolate Y3F, and in both cases the genes could be expressed in Escherichia coli to yield dioxygenase activity. Additional genes involved in the protocatechuate branch of the beta-ketoadipate pathway (pcaC, pcaQ, and pobA) were found to cluster with pcaGH in these two isolates. Pairwise sequence analysis of the pca genes revealed greater similarity between the two Roseobacter group isolates than between genes from either Roseobacter strain and soil bacteria. A degenerate PCR primer set targeting a conserved region within PcaH successfully amplified a fragment of pcaH from two additional Roseobacter group isolates, and Southern hybridization indicated the presence of pcaH in the remaining two isolates. This evidence of protocatechuate 3, 4-dioxygenase and the beta-ketoadipate pathway was found in all six Roseobacter isolates, suggesting widespread abilities to degrade aromatic compounds in this marine lineage.

Vertebrate homologs of Drosophila suppressor of fused interact with the gli family of transcriptional regulators.

The hedgehog (Hh) signaling pathway is crucial for pattern formation during metazoan development. Although originially characterized in Drosophila, vertebrate homologs have been identified for several, but not all, genes in the pathway. Analysis of mutants in Drosophila demonstrates that Suppressor of fused [Su(fu)] interacts genetically with genes encoding proteins in the Hh signal transduction pathway, and its protein product physically interacts with two of the proteins in the Hh pathway. We report here the molecular cloning and characterization of chicken and mouse homologs of Su(fu). The chick and mouse proteins are 27% identical and 53% similar at the amino acid level to the Drosophila melanogaster and Drosophila virilis proteins. Vertebrate Su(fu) is widely expressed in the developing embryo with higher levels in tissues that are known to be patterned by Hh signaling. The chick Su(fu) protein can physically interact with factors known to function in Hh signal transduction including the Drosophila serine/threonine kinase, Fused, and the vertebrate transcriptional regulators Gli1 and Gli3. This interaction may be significant for transcriptional regulation, as recombinant Su(fu) enhances the ability of Gli proteins to bind DNA in electrophoretic mobility shift assays.

areABC genes determine the catabolism of aryl esters in Acinetobacter sp. Strain ADP1.

Acinetobacter sp. strain ADP1 is able to grow on a range of esters of aromatic alcohols, converting them to the corresponding aromatic carboxylic acids by the sequential action of three inducible enzymes: an areA-encoded esterase, an areB-encoded benzyl alcohol dehydrogenase, and an areC-encoded benzaldehyde dehydrogenase. The are genes, adjacent to each other on the chromosome and transcribed in the order areCBA, were located 3.5 kbp upstream of benK. benK, encoding a permease implicated in benzoate uptake, is at one end of the ben-cat supraoperonic cluster for benzoate catabolism by the beta-ketoadipate pathway. Two open reading frames which may encode a transcriptional regulator, areR, and a porin, benP, separate benK from areC. Each are gene was individually expressed to high specific activity in Escherichia coli. The relative activities against different substrates of the cloned enzymes were, within experimental error, identical to that of wild-type Acinetobacter sp. strain ADP1 grown on either benzyl acetate, benzyl alcohol, or 4-hydroxybenzyl alcohol as the carbon source. The substrate preferences of all three enzymes were broad, encompassing a range of substituted aromatic compounds and in the case of the AreA esterase, different carboxylic acids. The areA, areB, and areC genes were individually disrupted on the chromosome by insertion of a kanamycin resistance cassette, and the rates at which the resultant strains utilized substrates of the aryl ester catabolic pathway were severely reduced as determined by growth competitions between the mutant and wild-type strains.

Mutations in catB, the gene encoding muconate cycloisomerase, activate transcription of the distal ben genes and contribute to a complex regulatory circuit in Acinetobacter sp. strain ADP1.

Mutants of the bacterium Acinetobacter sp. strain ADP1 were selected to grow on benzoate without the BenM transcriptional activator. In the wild type, BenM responds to benzoate and cis,cis-muconate to activate expression of the benABCDE operon, which is involved in benzoate catabolism. This operon encodes enzymes that convert benzoate to catechol, a compound subsequently degraded by cat gene-encoded enzymes. In this report, four spontaneous mutants were found to carry catB mutations that enabled BenM-independent growth on benzoate. catB encodes muconate cycloisomerase, an enzyme required for benzoate catabolism. Its substrate, cis,cis-muconate, is enzymatically produced from catechol by the catA-encoded catechol 1,2-dioxygenase. Muconate cycloisomerase was purified to homogeneity from the wild type and the catB mutants. Each purified enzyme was active, although there were differences in the catalytic properties of the wild type and variant muconate cycloisomerases. Strains with a chromosomal benA::lacZ transcriptional fusion were constructed and used to investigate how catB mutations affect growth on benzoate. All of the catB mutations increased cis,cis-muconate-activated ben gene expression in strains lacking BenM. A model is presented in which the catB mutations reduce muconate cycloisomerase activity during growth on benzoate, thereby increasing intracellular cis, cis-muconate concentrations. This, in turn, may allow CatM, an activator similar to BenM in sequence and function, to activate ben gene transcription. CatM normally responds to cis,cis-muconate to activate cat gene expression. Consistent with this model, muconate cylcoisomerase specific activities in cell extracts of benzoate-grown catB mutants were low relative to that of the wild type. Moreover, the catechol 1,2-dioxygenase activities of the mutants were elevated, which may result from CatM responding to the altered intracellular levels of cis,cis-muconate and increasing catA expression. Collectively, these results support the important role of metabolite concentrations in controlling benzoate degradation via a complex transcriptional regulatory circuit.