No abstract

No abstract

The single gene, auxin-resistant diageotropica (dgt) mutant of tomato displays a pleiotropic auxin-related phenotype that includes a slow gravitropic response, lack of lateral roots, reduced apical dominance, altered vascular development, and reduced fruit growth. Some auxin responses are unaltered in dgt plants, however, and the levels, metabolism, and transport of auxin appear normal, indicating that the Dgt gene encodes a component of a specific auxin signaling pathway. By combining map-based cloning with comparative microsynteny, we determined that the Dgt gene encodes a cyclophilin (CYP) (LeCYP1; gi:170439) that has not previously been identified as a component of auxin signaling and plant development. Each of the three known dgt alleles contains a unique mutation in the coding sequence of LeCyp1. Alleles dgt(1-1)and dgt(1-2) contain single nucleotide point mutations that generate an amino acid change (G137R) and a stop codon (W128stop), respectively, while dgt(dp) has an amino acid change (W128CDelta129-133) preceding a 15 bp deletion. Complementation of dgt plants with the wild-type LeCyp1 gene restored the wild-type phenotype. Each dgt mutation reduced or nullified the peptidyl-prolyl isomerase activity of the GST-LeCYP1 fusion proteins in vitro. RT-PCR and immunoblot analyses indicated that the dgt mutations do not affect the expression of LeCyp1 mRNA, but the accumulation of LeCYP1 protein is greatly reduced for all three mutant alleles. The CYP inhibitor, cyclosporin A, partially mimics the effects of the dgt mutation in inhibiting auxin-induced adventitious root initiation in tomato hypocotyl sections and reducing the auxin-induced expression of the early auxin response genes, LeIAA10 and 11. These observations confirm that the PPIase activity of the tomato CYP, LeCYP1, encoded by the Dgt gene is important for specific aspects of auxin regulation of plant growth, development, and environmental responses.

Several cyanobacteria adjust both the phycobiliprotein and linker protein composition of the phycobilisome, a light-harvesting complex in cyanobacteria and some eucaryotic algae, to maximize absorption of prevalent wavelengths of light. This process is called complementary chromatic adaptation. We sequenced the amino terminus of a linker polypeptide which is associated with phycocyanin and accumulates to high levels during growth of the cyanobacterium Fremyella diplosiphon in red light. A mixed oligonucleotide encoding a region of this amino terminus was synthesized and used to identify a fragment of F. diplosiphon genomic DNA encoding the linker polypeptide. This linker gene was located between two other linker genes and contiguous to the red-light-induced phycocyanin gene set. Sequences of all three linker genes are presented. These genes were transcribed together onto a large polycistronic mRNA which also encoded the red-light-induced phycocyanin subunits. The relationship of this transcript to the biogenesis of the phycobilisome when F. diplosiphon is grown under different conditions of illumination is discussed.

Association of (14)C-labelled indole-3-acetic acid (IAA) with membrane particles from zucchini (Cucurbita pepo L.) hypocotyls - previously described as "site III binding" (M. Jacobs and R. Hertel, 1978, Planta 142, 1-10) - is reinterpreted as a carrier-mediated uptake into closed and sealed vesicles driven by a pH gradient. Accumulation of the radioactive auxin is saturable, sensitive to the protonophore, carbonyl cyanide p-trifluoromethoxyphenyl hydrazone (FCCP), and to nigericin, and requires a pH gradient across the membranes with proton concentration greater outside than inside. The pH gradient decays within 1-2 h at 4°C and can be restored by re-equilibration of the particle preparation at more alkaline pH followed by return to more acidic medium. Osmotic shock and sonication release the IAA from the vesicles. 1-N-naphthylphthalamic acid (NPA) and 2,3,5-triiodobenzoic acid (TIBA), both inhibitors of auxin transport in vivo, increase the amount of net IAA accumulation in the vesicles, presumably by blocking efflux. Analogs of NPA less active or inactive in vivo are respectively less active or inactive in vitro. It is proposed that these membrane particles are outside-out plasma membrane vesicles, and that they perform the essential functions of auxin transport according to the chemiosmotic theory, with a specific, saturable proton symport uptake and an export anion carrier which is inhibited by NPA and TIBA.