IAA production during germination of Orobanche spp. seeds

Broomrapes (Orobanche spp.) are parasitic plants, whose growth and development fully depend on the nutritional connection established between the parasite and the roots of the respective host plant. Phytohormones are known to play a role in establishing the specific Orobanche-host plant interaction. The first step in the interaction is seed germination triggered by a germination stimulant secreted by the host-plant roots. We quantified indole-3-acetic acid (IAA) and abscisic acid (ABA) during the seed germination of tobacco broomrape (Orobanche ramosa) and sunflower broomrape (O. cumana). IAA was mainly released from Orobanche seeds in host-parasite interactions as compared to non-host-parasite interactions. Moreover, germinating seeds of O. ramosa released IAA as early as 24 h after the seeds were exposed to the germination stimulant, even before development of the germ tube. ABA levels remained unchanged during the germination of the parasites' seeds. The results presented here show that IAA production is probably part of a mechanism triggering germination upon the induction by the host factor, thus resulting in seed germination.     

Catalytically Increased Prebiotic Peptide Formation: Ditryptophan,Dilysine, and Diserine

“Mutual” amino acid catalysis of glycine on the formation of ditryptophan, dilysine, and diserine in the prebiotically relevant Salt-Induced Peptide Formation (SIPF) Reaction was investigated varying the starting concentration and chirality of the educt amino acid, and analyzing the increase of yield resulting from this catalytic effect. Our results show the possibility of an amplified diverse pool of peptides being available for chemical evolution of larger peptides and proteins using also these more complicated amino acids for the evolution of more complex functions in future biochemical cycles and thus for the emergence of life. Catalytic effects are especially high in the case of serine, the most basic amino acid of the three, but are also significant for the other two examples investigated in the present work. Besides that, especially for serine, but also in the case of tryptophan, differences in catalytic yield increase according to the chiral form of the amino acid used could be observed.     

Genotypic and phenotypic characterization of a biofilm-forming Serratia plymuthica isolate from a raw vegetable processing line

Recently, we isolated from a raw vegetable processing line a Serratia strain with strong biofilm-forming capacity and which produced N-acyl-L-homoserine lactones (AHLs). Within the Enterobacteriaceae, strains of the genus Serratia are a frequent cause of human nosocomial infections; in addition, biofilm formation is often associated with persistent infections. In the current report, we describe the detailed characterization of the isolate using a variety of genotypic and phenotypic criteria. Although the strain was identified as Serratia plymuthica on the basis of its small subunit ribosomal RNA (16S rRNA) gene sequence, it differed from the S. plymuthica type strain in production of pigment and antibacterial compounds, and in AHL production profile. Nevertheless, the identification as S. plymuthica could be confirmed by gyrB phylogeny and DNA:DNA hybridization.     

Voltage-dependent anion-selective channel 1 (VDAC1)--a mitochondrial protein, rediscovered as a novel enzyme in the plasma membrane

The eukaryotic porin or voltage-dependent anion-selective channel (VDAC1) is a pore-forming protein discovered twenty five years ago in the mitochondrial outer membrane. Its gene in eukaryotes is known, but its tertiary structure has never been solved. Structure predictions highlight the presence of several amphipathic beta-strands possibly organised in a beta-barrel. VDAC1 has recently been described as being a NADH:ferricyanide reductase in the plasma membrane. There it affects the regulation of cell growth and death. Physiological cell death (apoptosis) has become a major research focus of biomedical research. Regulation of the enzyme will have impacts on cancer and autoimmune diseases (insufficient apoptosis) as well as neurodegenerative diseases (excessive apoptosis). VDAC1 in the plasma membrane establishes a novel level of apoptosis regulation putatively via its redox activity.     

Transcriptional analysis of the Azospirillum brasilense indole-3-pyruvate decarboxylase gene and identification of a cis-acting sequence involved in auxin responsive expression

Expression of the Azospirillum brasilense ipdC gene, encoding an indole-3-pyruvate decarboxylase, a key enzyme in the production of indole-3-acetic acid (IAA) in this bacterium, is upregulated by IAA. Here, we demonstrate that the ipdC gene is the promoter proximal gene in a bicistronic operon. Database searches revealed that the second gene of this operon, named iaaC, is well conserved evolutionarily and that the encoded protein is homologous to the Escherichia coli protein SCRP-27A, the zebrafish protein ES1, and the human protein KNP-I/GT335 (HES1), all of unknown function and belonging to the DJ-1/PfpI superfamily. In addition to this operon structure, iaaC is also transcribed monocistronically. Mutation analysis of the latter gene indicated that the encoded protein is involved in controlling IAA biosynthesis but not ipdC expression. Besides being upregulated by IAA, expression of the ipdC-iaaC operon is pH dependent and maximal at acidic pH. The ipdC promoter was studied using a combination of deletion analyses and site-directed mutagenesis. A dyadic sequence (ATTGTTTC(GAAT)GAAACAAT), centered at -48 was demonstrated to be responsible for the IAA inducibility. This bacterial auxin-responsive element does not control the pH-dependent expression of ipdC-iaaC.     

PKA and Sch9 control a molecular switch important for the proper adaptation to nutrient availability

In the yeast Saccharomyces cerevisiae, PKA and Sch9 exert similar physiological roles in response to nutrient availability. However, their functional redundancy complicates to distinguish properly the target genes for both kinases. In this article, we analysed different phenotypic read-outs. The data unequivocally showed that both kinases act through separate signalling cascades. In addition, genome-wide expression analysis under conditions and with strains in which either PKA and/or Sch9 signalling was specifically affected, demonstrated that both kinases synergistically or oppositely regulate given gene targets. Unlike PKA, which negatively regulates stress-responsive element (STRE)- and post-diauxic shift (PDS)-driven gene expression, Sch9 appears to exert additional positive control on the Rim15-effector Gis1 to regulate PDS-driven gene expression. The data presented are consistent with a cyclic AMP (cAMP)-gating phenomenon recognized in higher eukaryotes consisting of a main gatekeeper, the protein kinase PKA, switching on or off the activities and signals transmitted through primary pathways such as, in case of yeast, the Sch9-controlled signalling route. This mechanism allows fine-tuning various nutritional responses in yeast cells, allowing them to adapt metabolism and growth appropriately.     

From earth's primitive atmosphere to chiral peptides--the origin of precursors for life

To re-enact the long way to the origin of life with today's chemical methods, many steps have to be investigated in the light of a primordial scenario deduced from geochemical research. After the formation of our planet and its atmosphere, prebiotic chemical evolution started its course with the formation of the first building blocks for the formation of biomolecules. In the case of proteins, those building blocks were amino acids that had to be formed in the primitive atmosphere, and then had to react to peptides and proteins as the main pillar of first life. In this paper, we describe the processes in the primordial atmosphere according to contemporary geochemical knowledge leading to the synthesis of amino acids until the formation of homochiral peptides, and, thus, show a plausible pathway towards the origin of life.