title: Possible dual regulatory circuits involving AtS6K1 in the regulation of plant cell cycle and growth.
abstract: The role of Arabidopsis S6 Kinase 1 (AtS6K1), a downstream target of TOR kinase, in controlling plant growth and ribosome biogenesis was characterized after generating transgenic plants expressing AtS6K1 under auxin-inducible promoter. Down regulation of selected cell cycle regulatory genes upon auxin treatment was observed in the transgenic plants, confirming the negative regulatory role of AtS6K1 in the plant cell cycle progression reported earlier. Callus tissues established from these transgenic plants grew to larger cell masses with more number of enlarged cells than untransformed control, demonstrating functional implication of AtS6K1 in the control of plant cell size. The observed negative correlation between the expression of AtS6K1 and the cell cycle regulatory genes, however, was completely reversed in protoplasts generated from the transgenic plants expressing AtS6K1, suggesting a possible existence of dual regulatory mechanism of the plant cell cycle regulation mediated by AtS6K1. An alternative method of kinase assay, termed "substrate-mediated kinase pull down", was employed to examine the additional phosphorylation on other domains of AtS6K1 and verified the phosphorylation of both amino- and carboxy-terminal domains, which is a novel finding regarding the phosphorylation target sites on plant S6Ks by upstream regulatory kinases. In addition, this kinase assay under the stress conditions revealed the salt- and sugar-dependencies of AtS6K1 phosphorylations.
authors.affiliation: Department of Biological Science, Sookmyung Women's University, Seoul 140-742, Korea.
authors.forename: Yun-jeong
authors.initials: YJ
authors.lastname: Shin
authors.forename: Sunghan
authors.initials: S
authors.lastname: Kim
authors.forename: Hui
authors.initials: H
authors.lastname: Du
authors.forename: Soonyoung
authors.initials: S
authors.lastname: Choi
authors.forename: Desh Pal S
authors.initials: DP
authors.lastname: Verma
authors.forename: Choong-Ill
authors.initials: CI
authors.lastname: Cheon
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects / Q000235:genetics*; D049108:Cell Enlargement / Q000187:drug effects; D048429:Cell Size / Q000187:drug effects; D004275:DNA, Ribosomal / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D007210:Indoleacetic Acids / Q000494:pharmacology; D010766:Phosphorylation; D059828:Plant Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D063245:Plant Development / Q000502:physiology*; D010937:Plant Growth Regulators / Q000494:pharmacology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D011523:Protoplasts / Q000187:drug effects / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000235:genetics / Q000378:metabolism*; D012270:Ribosomes / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D029681:Arabidopsis Proteins; D004275:DNA, Ribosomal; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D010940:Plant Proteins; D019893:Ribosomal Protein S6 Kinases