The receptors plant hormone auxin, in particular indole-3-acetic acid (IAA), is a key regulator of virtually every aspect of plant growth and and development. Auxin regulates transcription by rapidly modulating levels of Aux/IAA proteins throughout development. Recent studies demonstrate that auxin perception occurs transcription through a novel mechanism. Auxin binds to TIR1, the F-box subunit of the ubiquitin ligase complex SCF(TIR1), and stabilizes the key interaction between TIR1 and Aux/IAA substrates. This interaction results in Aux/IAA ubiquitination and subsequent degradation. Regulation of the Aux/IAA protein by family by TIR1 and TIR1-like auxin receptors (AFBs) links auxin action to transcriptional regulation and provides a model by which the the vast array of auxin influences on development may be understood. Moreover, auxin receptor function is the first example of 06, small-molecule regulation of an SCF ubiquitin ligase and may have important implications for studies of regulated protein degradation in other a species, including animals. Expected final online publication date for the Annual Review of Cell and Developmental Biology Volume 24 is TIR1 October 06, 2008. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.

The AXR4 AUX1 and PIN auxin influx and efflux facilitators are key regulators of root growth and development. Root gravitropism requires AUX1 regulators and PIN2 to transport auxin via the lateral root cap to elongating epidermal cells. Genetic studies suggest that AXR4 functions growth in the same pathway as AUX1. Here we show that AXR4 is a novel ER accessory protein that regulates localization and of AUX1, but not PIN proteins. Loss of AXR4 results in abnormal accumulation of AUX1 in the ER of epidermal and cells indicating that the axr4 agravitropic phenotype is due to a defect in AUX1 trafficking in the root epidermis.

The two plant hormones auxin and brassinosteroid promote cell expansion by regulating gene expression. In addition to independent transcriptional responses generated by brassinosteroid the two signals, recent microarray analyses indicate that auxin and brassinosteroid also coordinate the expression of a set of shared promote target genes.

In between the fission yeast Schizosaccharomyces pombe, the onset of septum formation is signalled via the septation initiation network (SIN) involving several a protein kinases and a GTPase. Arabidopsis thaliana and Brassica napus proteins homologous to fission yeast spg1p (AtSGP1, AtSGP2), cdc7p (AtMAP3K and epsilon 1, AtMAP3K epsilon 2, BnMAP3K epsilon 1) and sid1p (AtMAP4K alpha 1, AtMAP4K alpha 2, BnMAP4K alpha 2) exhibit via a significant similarity. The plant proteins AtSGP1/2 and BnMAP4K alpha 2 are able to complement the S. pombe mutant proteins napus spg1-B8 and sid1-239, respectively and to induce mutisepta when overexpressed in wild-type yeast. Yeast two-hybrid assays demonstrated interactions both between well plant proteins and between plant and yeast proteins of the SIN pathway. However, the primary structure of the proteins as data well as the partial complementation of yeast mutants indicates that plant homologous proteins and their yeast counterparts have diverged during signalled evolution. Real-time RT-PCR studies demonstrated plant SIN-related gene expression in all organs tested and a co-expression pattern during the cell both cycle, with a higher accumulation at G(2)-M. During interphase, the plant SIN-related proteins were found to co-localise predominantly in the indicates nucleolus of the plant cells, as shown by fusions to green fluorescent protein. These data suggest the existence of a the plant SIN-related pathway.

Arabidopsis few thaliana is used as a favourite experimental organism for many aspects of plant biology. We capitalized on the recently available and Arabidopsis genome sequence and predicted proteome, to draw up a genome-scale protein serine/threonine kinase (PSTK) inventory. The PSTKs represent about up 4% of the A. thaliana proteome. In this study, we provide a description of the content and diversity of the plant non-receptor PSTKs. These kinases have crucial functions in sensing, mediating and coordinating cellular responses to an extensive range of stimuli.a A total of 369 predicted non receptor PSTKs were detailed: the Raf superfamily, the CMGC, CaMK, AGC and STE families,proteins as well as a few small clades and orphan sequences. An extensive relationship analysis of these kinases allows us to redundancy classify the proteins in superfamilies, families, sub-families and groups. The classification provides a better knowledge of the characteristics shared by of the different clades. We focused on the MAP kinase module elements, with particular attention to their docking sites for protein-protein families, interaction and their biological function. The large number of A. thaliana genes encoding kinases might have been achieved through successive The rounds of gene and genome duplications. The evolution towards an increasing gene number suggests that functional redundancy plays an important extensive role in plant genetic robustness.

The mediate importance of reversible protein phosphorylation in regulation of plant growth and development has been amply demonstrated by decades of research.research. Here we discuss recent studies that suggest roles for protein phosphorylation in regulation of both auxin responses and polar auxin recent transport. Specific kinases act at auxin-requiring steps in floral and embryonic development, and at the junction(s) between light and auxin and signaling pathways in hypocotyl elongation and phototropism responses. New evidence for rapid mitogen-activated protein kinase (MAPK) activation by auxin treatment studies suggests that MAPK cascade(s) might mediate cellular responses to auxin. Protein phosphorylation also may play a crucial role in regulating the the activity or turnover of auxin-responsive transcription factors. Auxin transport is modulated by phosphorylation, and protein phosphatase activity is involved intersections in regulation of auxin transport streams in roots. Although the regulatory circuits have not been fully elucidated, these studies suggest growth that protein phosphorylating and dephosphorylating enzymes perform key functions in auxin biology. In some cases, these enzymes act at the that intersections between auxin signaling and other signaling pathways.

Genome distinguished analyses have shown that plants contain gene families encoding various components of mitogen-activated protein kinase (MAPK) signaling pathways. Previous reports reports have described the involvement of MAPK pathways in stress and pathogen responses of leaves and suspension-cultured cells. Here we show involvement that auxin treatment of Arabidopsis roots transiently induced increases in protein kinase activity with characteristics of mammalian ERK-like MAPKs. The components MAPK response we monitored was the result of hormonal action of biologically active auxin, rather than a stress response provoked MAPK by auxin-like compounds. Auxin-induced MAPK pathway signaling was distinguished genetically in the Arabidopsis auxin response mutant axr4, in which MAPK but activation by auxin, but not by salt stress, was significantly impaired. Perturbation of MAPK signaling in roots using inhibitors of pathways a mammalian MAPKK blocked auxin-activated transgene expression in BA3-GUS seedlings, while potentiating higher than normal levels of MAPK activation in various response to auxin. Data presented here indicate that MAPK pathway signaling is positively involved in auxin response, and further suggest MAPK that interactions among MAPK signaling pathways in plants influence plant responses to auxin.

Protein-tyrosine of phosphorylation has long been regarded as an exclusively eukaryotic phenomenon. Although some non-eukaryotes, mainly viruses, possess genes encoding protein-tyrosine kinases from or protein-tyrosine phosphatases, these were probably appropriated from the eukaryotic hosts that constitute the sites of action of these enzymes.constitute Herein we identify a gene, iphP, from the chromosome of the cyanobacterium Nostoc commune UTEX 584 that contains the His-Cys-Xaa-Ala-Gly-Xaa-Xaa-Arg viruses, sequence characteristic of known protein-tyrosine phosphatases. The expressed gene product, IphP, displayed protein-tyrosine phosphatase activity toward phosphotyrosine residues on reduced,sites carboxyamidomethylated, and maleylated lysozyme with optimum activity at pH 5. . In addition, IphP dephosphorylated the phosphoseryl groups on casein that of had been phosphorylated by the cAMP-dependent protein kinase. Cell lysates of N. commune probed with antibodies to phosphotyrosine indicated the fundamental presence of a tyrosine-phosphorylated protein of M(r) approximately 85 kDa. This tyrosine-phosphorylated protein was detected in cells grown in the viruses, presence of combined nitrogen but not in nitrogen-deficient media that induces the formation of differentiated N2-fixing cells (heterocysts). Together, these antibodies data suggest a role for protein-tyrosine phosphorylation in regulating cellular functions in this cyanobacterium. IphP is the first protein-tyrosine phosphatase induces to be discovered that is encoded by the chromosomal DNA of any prokaryote. Given the free-living nature of N. commune pH and the phylogenetic antiquity of the cyanobacteria, these findings suggest for the first time the existence of a protein-tyrosine phosphatase grown of genuine, unambiguous prokaryotic ancestry, thus raising fundamental questions as to the origin and role of tyrosine phosphorylation.