A combinatorial TIR1/AFB–Aux/IAA co-receptor system for differential sensing of auxin

The plant hormone auxin regulates virtually every aspect of plant growth and development. Auxin acts by binding the F-box protein transport inhibitor response 1 (TIR1) and promotes the degradation of the AUXIN/INDOLE-3-ACETIC ACID (Aux/IAA) transcriptional repressors. Here we show that efficient auxin binding requires assembly of an auxin co-receptor complex consisting of TIR1 and an Aux/IAA protein. Heterologous experiments in yeast and quantitative IAA binding assays using purified proteins showed that different combinations of TIR1 and Aux/IAA proteins form co-receptor complexes with a wide range of auxin-binding affinities. Auxin affinity seems to be largely determined by the Aux/IAA. As there are 6 TIR1/AUXIN SIGNALING F-BOX proteins (AFBs) and 29 Aux/IAA proteins in Arabidopsis thaliana, combinatorial interactions may result in many co-receptors with distinct auxin-sensing properties. We also demonstrate that the AFB5–Aux/IAA co-receptor selectively binds the auxinic herbicide picloram. This co-receptor system broadens the effective concentration range of the hormone and may contribute to the complexity of auxin response

Arabidopsis Ovate Family Proteins, a Novel Transcriptional Repressor Family, Control Multiple Aspects of Plant Growth and Development

, AtOFP4 has been shown to regulate secondary cell wall formation by interact with KNOTTED1-LIKE HOMEODOMAIN PROTEIN 7 (KNAT7), and AtOFP5 has been shown to regulate the activity of a BEL1-LIKEHOMEODOMAIN 1(BLH1)-KNAT3 complex during early embryo sac development, but little is known about the function of other AtOFPs. genes may also have diverse functions in regulating plant growth and development. Further analysis suggested that AtOFP1 regulates cotyledon development in a postembryonic manner, and global transcript profiling revealed that it suppress the expression of many other genes.Our results showed that AtOFPs function as transcriptional repressors and they regulate multiple aspects of plant growth and development. These results provided the first overview of a previously unknown transcriptional repressor family, and revealed their possible roles in plant growth and development

Identification and Expression of the Family of Classical Protein-Tyrosine Phosphatases in Zebrafish

Protein-tyrosine phosphatases (PTPs) have an important role in cell survival, differentiation, proliferation, migration and other cellular processes in conjunction with protein-tyrosine kinases. Still relatively little is known about the function of PTPs in vivo. We set out to systematically identify all classical PTPs in the zebrafish genome and characterize their expression patterns during zebrafish development. We identified 48 PTP genes in the zebrafish genome by BLASTing of human PTP sequences. We verified all in silico hits by sequencing and established the spatio-temporal expression patterns of all PTPs by in situ hybridization of zebrafish embryos at six distinct developmental stages. The zebrafish genome encodes 48 PTP genes. 14 human orthologs are duplicated in the zebrafish genome and 3 human orthologs were not identified. Based on sequence conservation, most zebrafish orthologues of human PTP genes were readily assigned. Interestingly, the duplicated form of ptpn23, a catalytically inactive PTP, has lost its PTP domain, indicating that PTP activity is not required for its function, or that ptpn23b has lost its PTP domain in the course of evolution. All 48 PTPs are expressed in zebrafish embryos. Most PTPs are maternally provided and are broadly expressed early on. PTP expression becomes progressively restricted during development. Interestingly, some duplicated genes retained their expression pattern, whereas expression of other duplicated genes was distinct or even mutually exclusive, suggesting that the function of the latter PTPs has diverged. In conclusion, we have identified all members of the family of classical PTPs in the zebrafish genome and established their expression patterns. This is the first time the expression patterns of all members of the large family of PTP genes have been established in a vertebrate. Our results provide the first step towards elucidation of the function of the family of classical PTPs

Undergraduate research. Genomics Education Partnership

The Genomics Education Partnership offers an inclusive model for undergraduate research experiences incorporated into the academic year science curriculum, with students pooling their work to contribute to international data bases

A soybean sucrose binding protein independently mediates nonsaturable sucrose uptake in yeast.

Heterologous expression of a cDNA encoding a 62-kD soybean sucrose binding protein in yeast demonstrates that this protein, independent of other plant proteins, mediates sucrose uptake across the plasma membrane. Sucrose binding protein-mediated sucrose uptake is nonsaturable up to 30 mM sucrose, is specific for sucrose, and is relatively insensitive to treatment with sulfhydryl-modifying reagents. Alteration of the external pH or pretreatment of the yeast cells with protonophores did not significantly affect the rate of 14C-sucrose uptake. This demonstrates that sucrose binding protein-mediated sucrose uptake is not dependent on H+ movement and delineates it from other plant sucrose transporters. Physiological characterization of sucrose uptake into higher plant cells has shown the presence of both saturable and nonsaturable uptake components. The nonsaturable mechanism is relatively insensitive to external pH, pretreatment with protonophores, and treatment with sulfhydryl-modifying reagents. Sucrose binding protein-mediated sucrose uptake in yeast mimics this physiologically described, but mechanistically undefined, nonsaturable sucrose uptake mechanism in higher plants. Functional characterization of the sucrose binding protein thus defines both a novel component of sucrose uptake and provides important insight into this nonsaturable sucrose uptake mechanism, which has remained enigmatic since its physiological description

age Mutants of Arabidopsis exhibit altered auxin-regulated gene expression.

An Arabidopsis transgenic line was constructed expressing beta-glucuronidase (GUS) via the auxin-responsive domains (AuxRDs) A and B (BA-GUS) of the PS-IAA4/5 gene in an indoleacetic acid (IAA)-dependent fashion. GUS expression was preferentially enhanced in the root elongation zone after treatment of young seedlings with 10(-7) M IAA. Expression of the BA-GUS gene in the axr1, axr4, and aux1 mutants required 10- to 100-fold higher auxin concentration than that in the wild-type background. GUS expression was nil in the axr 2 and axr 3 mutants. The transgene was used to isolate mutants exhibiting altered auxin-responsive gene expression (age). Two mutants, age1 and age2, were isolated and characterized. age1 showed enhanced sensitivity to IAA, with strong GUS expression localized in the root elongation zone in the presence of 10(-8) M IAA. In contrast, age2 exhibited ectopic GUS expression associated with the root vascular tissue, even in the absence of exogenous IAA. Morphological and molecular analyses indicated that the age1 and age2 alleles are involved in the regulation of gene expression in response to IAA