title: Perturbation of cytokinin and ethylene-signalling pathways explain the strong rooting phenotype exhibited by Arabidopsis expressing the Schizosaccharomyces pombe mitotic inducer, cdc25.
abstract: BACKGROUND
  Entry into mitosis is regulated by cyclin dependent kinases that in turn are phosphoregulated. In most eukaryotes, phosphoregulation is through WEE1 kinase and CDC25 phosphatase. In higher plants a homologous CDC25 gene is unconfirmed and hence the mitotic inducer Schizosaccharomyces pombe (Sp) cdc25 has been used as a tool in transgenic plants to probe cell cycle function. Expression of Spcdc25 in tobacco BY-2 cells accelerates entry into mitosis and depletes cytokinins; in whole plants it stimulates lateral root production. Here we show, for the first time, that alterations to cytokinin and ethylene signaling explain the rooting phenotype elicited by Spcdc25 expression in Arabidopsis.
  
  
  RESULTS
  Expressing Spcdc25 in Arabidopsis results in increased formation of lateral and adventitious roots, a reduction of primary root width and more isodiametric cells in the root apical meristem (RAM) compared with wild type. Furthermore it stimulates root morphogenesis from hypocotyls when cultured on two way grids of increasing auxin and cytokinin concentrations. Microarray analysis of seedling roots expressing Spcdc25 reveals that expression of 167 genes is changed by > 2-fold. As well as genes related to stress responses and defence, these include 19 genes related to transcriptional regulation and signaling. Amongst these was the up-regulation of genes associated with ethylene synthesis and signaling. Seedlings expressing Spcdc25 produced 2-fold more ethylene than WT and exhibited a significant reduction in hypocotyl length both in darkness or when exposed to 10 ppm ethylene. Furthermore in Spcdc25 expressing plants, the cytokinin receptor AHK3 was down-regulated, and endogenous levels of iPA were reduced whereas endogeous IAA concentrations in the roots increased.
  
  
  CONCLUSIONS
  We suggest that the reduction in root width and change to a more isodiametric cell phenotype in the RAM in Spcdc25 expressing plants is a response to ethylene over-production. The increased rooting phenotype in Spcdc25 expressing plants is due to an increase in the ratio of endogenous auxin to cytokinin that is known to stimulate an increased rate of lateral root production. Overall, our data reveal important cross talk between cell division and plant growth regulators leading to developmental changes.
authors.affiliation: School of Biosciences, Cardiff University, Cardiff CF10 3AT, UK.
authors.forename: Natasha D
authors.initials: ND
authors.lastname: Spadafora
authors.forename: David
authors.initials: D
authors.lastname: Parfitt
authors.forename: Angela
authors.initials: A
authors.lastname: Marchbank
authors.forename: Sherong
authors.initials: S
authors.lastname: Li
authors.forename: Leonardo
authors.initials: L
authors.lastname: Bruno
authors.forename: Rhys
authors.initials: R
authors.lastname: Vaughan
authors.forename: Jeroen
authors.initials: J
authors.lastname: Nieuwland
authors.forename: Vicky
authors.initials: V
authors.lastname: Buchanan-Wollaston
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Herbert
authors.forename: Maria Beatrice
authors.initials: MB
authors.lastname: Bitonti
authors.forename: John
authors.initials: J
authors.lastname: Doonan
authors.forename: Diego
authors.initials: D
authors.lastname: Albani
authors.forename: Els
authors.initials: E
authors.lastname: Prinsen
authors.forename: Dennis
authors.initials: D
authors.lastname: Francis
authors.forename: Hilary J
authors.initials: HJ
authors.lastname: Rogers
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins; D003583:Cytokinins / Q000378:metabolism* / Q000494:pharmacology; D003624:Darkness; D005030:Ethylenes / Q000378:metabolism* / Q000494:pharmacology; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D000071677:Histidine Kinase; D018546:Hypocotyl / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D007210:Indoleacetic Acids / Q000378:metabolism / Q000494:pharmacology; D008938:Mitosis; D010641:Phenotype; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D012568:Schizosaccharomyces / Q000235:genetics; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014158:Transcription, Genetic
chemical_list: D029681:Arabidopsis Proteins; D003583:Cytokinins; D005030:Ethylenes; D007210:Indoleacetic Acids; D029702:Schizosaccharomyces pombe Proteins; C036216:ethylene; D011494:Protein Kinases; D000071677:Histidine Kinase; C000605493:AHK3 protein, Arabidopsis; C570820:Cdc25 protein, S pombe; D010749:Phosphoprotein Phosphatases