Search

SKP1-Cullin1-F-box protein (SCF) ubiquitin-ligases regulate numerous aspects of eukaryotic growth and development. Cullin-Associated and Neddylation-Dissociated (CAND1) modulates SCF function through its interactions with the CUL1 subunit. Although biochemical studies with human CAND1 suggested that CAND1 plays a negative regulatory role by sequestering CUL1 and preventing SCF complex assembly, genetic studies in Arabidopsis have shown that cand1 mutants exhibit reduced SCF activity, demonstrating that CAND1 is required for optimal SCF function in vivo. Together, these genetic and biochemical studies have suggested a model of CAND1-mediated cycles of SCF complex assembly and disassembly. Here, using the [SCF.sup.TIR1] complex of the Arabidopsis auxin response pathway, we test the SCF cycling model with Arabidopsis mutant derivatives of CAND1 and CUL1 that have opposing effects on the CAND1-CUL1 interaction. We find that the disruption of the CAND1-CUL1 interaction results in an increased abundance of assembled [SCF.sup.TIR1] complex. In contrast, stabilization of the CAND1-CUL1 interaction diminishes [SCF.sup.TIR1] complex abundance. The fact that both decreased and increased CAND1-CUL1 interactions result in reduced [SCF.sup.TIR1] activity in vivo strongly supports the hypothesis that CAND1-mediated cycling is required for optimal SCF function. auxin | SCFTIR1 | ubiquitin-ligase | COP9 signalosome

By the end of the 21st century the concentration of greenhouse gases from human activity in Earth's atmosphere is expected to double from preindustrial values. Many believe this increase will [...]

Author(s): William M. Gray [1, 2]; Stefan Kepinski [2, 3]; Dean Rouse [3, 4]; Ottoline Leyser [3]; Mark Estelle (corresponding author) [1] Plant development requires the coordinated regulation of cell [...]

The plant hormone auxin regulates many aspects of growth and development. Despite the importance of this hormone, the molecular basis for auxin action has remained elusive. Recent advances using molecular genetics in Arabidopsis have begun to elucidate the mechanisms involved in auxin signaling. These results suggest that protein degradation by the ubiquitin pathway has a central role in auxin response.

An SCF ubiquitin-ligase complex required for auxin, that is indole-3-acetic acid (IAA), response in Arabidposis thaliana has been identtified. Auxin is a plant hormone that regulates various aspects of plant growth/development and mutations in AK1 (ital) or TIRI1 (ital) bring a decrease in auxin response. Overexpression of TIR1 enhances auxin response, which might indicate that SCF (super.TIR1) is a limiting factor. New support exists for a model in which auxin activity is dependent on the regulated proteolysis of repressor proteins.

Key regulatory proteins need to be modified by ubiquitin or a related protein for appropriate auxin response in Arabidopsis. Experiments with Transport Inhibitor Response 1 (TIR1) mutants underlines the role of this gene for auxin-response. The mutants did not have several of the growth responses moderated by auxin. Sequence comparisons suggests links between this gene, the yeast protein Grr1p and the human protein SKP2.

Summary: Plants employ an array of intricate and hierarchical signaling cascades to perceive and transduce informational cues to synchronize and tailor adaptive responses. Systemic stress response (SSR) is a recognized complex signaling and response network quintessential to plant's local and distal responses to environmental triggers; however, the identity of the initiating signals has remained fragmented.Here, we show that both biotic (aphids and viral pathogens) and abiotic (high light and wounding) stresses induce accumulation of the plastidial‐retrograde‐signaling metabolite methylerythritol cyclodiphosphate (MEcPP), leading to reduction of the phytohormone auxin and the subsequent decreased expression of the phosphatase PP2C.D1.This enables phosphorylation of mitogen‐activated protein kinases 3/6 and the consequential induction of the downstream events ultimately, resulting in biosynthesis of the two SSR priming metabolites pipecolic acid and N‐hydroxy‐pipecolic acid.This work identifies plastids as a major initiation site, and the plastidial retrograde signal MEcPP as an initiator of a multicomponent signaling cascade potentiating the biosynthesis of SSR activators, in response to biotic and abiotic triggers. [ABSTRACT FROM AUTHOR]

This paper describes a predictive relationship between West African rainfall and U.S. hurricane-spawned destruction, which is based on information for the 42-yr period 1949-90. It is shown that above-average rainfall during the previous year along the Gulf of Guinea, in combination with above-average rainfall in the western Sahel during June and July, is linked to hurricane-spawned destruction along the U.S. East Coast occurring after 1 August, which is 10-20 times greater than in years when pre-1 August precipitation for these West African regions is below average. Similar hurricane-spawned damage along the U.S. Gulf Coast shows only a negligible relationship with African rainfall. Hurricane-caused deaths for both U.S. coastal regions also show a similar association with West African rainfall.

Growth regulation tailors development in plants to their environment. A prominent example of this is the response to gravity, in which shoots bend up and roots bend down1. This paradox is based on opposite effects of the phytohormone auxin, which promotes cell expansion in shoots while inhibiting it in roots via a yet unknown cellular mechanism2. Here, by combining microfluidics, live imaging, genetic engineering and phosphoproteomics in Arabidopsis thaliana, we advance understanding of how auxin inhibits root growth. We show that auxin activates two distinct, antagonistically acting signalling pathways that converge on rapid regulation of apoplastic pH, a causative determinant of growth. Cell surface-based TRANSMEMBRANE KINASE1 (TMK1) interacts with and mediates phosphorylation and activation of plasma membrane H+-ATPases for apoplast acidification, while intracellular canonical auxin signalling promotes net cellular H+ influx, causing apoplast alkalinization. Simultaneous activation of these two counteracting mechanisms poises roots for rapid, fine-tuned growth modulation in navigating complex soil environments.Auxin rapidly modulates root growth through simultaneous activation of two opposing mechanisms—TMK1-mediated apoplast acidification and TIR1/AFB-mediated apoplast alkalinization. [ABSTRACT FROM AUTHOR]

Abstract Background Labeling whole Arabidopsis (Arabidopsis thaliana) plants to high enrichment with 13C for proteomics and metabolomics applications would facilitate experimental approaches not possible by conventional methods. Such a system would use the plant's native capacity for carbon fixation to ubiquitously incorporate 13C from 13CO2 gas. Because of the high cost of 13CO2 it is critical that the design conserve the labeled gas. Results A fully enclosed automated plant growth enclosure has been designed and assembled where the system simultaneously monitors humidity, temperature, pressure and 13CO2 concentration with continuous adjustment of humidity, pressure and 13CO2 levels controlled by a computer running LabView software. The enclosure is mounted on a movable cart for mobility among growth environments. Arabidopsis was grown in the enclosure for up to 8 weeks and obtained on average >95 atom% enrichment for small metabolites, such as amino acids and >91 atom% for large metabolites, including proteins and peptides. Conclusion The capability of this labeling system for isotope dilution experiments was demonstrated by evaluation of amino acid turnover using GC-MS as well as protein turnover using LC-MS/MS. Because this 'open source' Arabidopsis 13C-labeling growth environment was built using readily available materials and software, it can be adapted easily to accommodate many different experimental designs.

Partially replicates Elkind and Bowen's (1979) investigation of adolescent egocentrism. Studies the relations between imaginary audience and operational thought by testing children and adolescents on a Piagetian-based written test of operational thought and the Imaginary Audience Scale. (Author/AS)

Administered the Adolescent Egocentrism Scale (AES) to middle and high school students (N=129). Found partial support for Inhelder and Piaget's and Elkind's views that adolescent egocentrism is a function of beginning formal operations. Discusses the difficulty of assessing the true thoughts/feelings of persons who are worried how they will appear to others. (Author/ABB)