title: The Arabidopsis D-type cyclin CYCD2;1 and the inhibitor ICK2/KRP2 modulate auxin-induced lateral root formation.
abstract: The integration of cell division in root growth and development requires mediation of developmental and physiological signals through regulation of cyclin-dependent kinase activity. Cells within the pericycle form de novo lateral root meristems, and D-type cyclins (CYCD), as regulators of the G₁-to-S phase cell cycle transition, are anticipated to play a role. Here, we show that the D-type cyclin protein CYCD2;1 is nuclear in Arabidopsis thaliana root cells, with the highest concentration in apical and lateral meristems. Loss of CYCD2;1 has a marginal effect on unstimulated lateral root density, but CYCD2;1 is rate-limiting for the response to low levels of exogenous auxin. However, while CYCD2;1 expression requires sucrose, it does not respond to auxin. The protein Inhibitor-Interactor of CDK/Kip Related Protein2 (ICK2/KRP2), which interacts with CYCD2;1, inhibits lateral root formation, and ick2/krp2 mutants show increased lateral root density. ICK2/KRP2 can modulate the nuclear levels of CYCD2;1, and since auxin reduces ICK2/KRP2 protein levels, it affects both activity and cellular distribution of CYCD2;1. Hence, as ICK2/KRP2 levels decrease, the increase in lateral root density depends on CYCD2;1, irrespective of ICK2/CYCD2;1 nuclear localization. We propose that ICK2/KRP2 restrains root ramification by maintaining CYCD2;1 inactive and that this modulates pericycle responses to auxin fluctuations.
authors.affiliation: Cardiff School of Biosciences, Cardiff University, CF103AX Cardiff, United Kingdom.
authors.forename: Luis
authors.initials: L
authors.lastname: Sanz
authors.forename: Walter
authors.initials: W
authors.lastname: Dewitte
authors.forename: Celine
authors.initials: C
authors.lastname: Forzani
authors.forename: Farah
authors.initials: F
authors.lastname: Patell
authors.forename: Jeroen
authors.initials: J
authors.lastname: Nieuwland
authors.forename: Bo
authors.initials: B
authors.lastname: Wen
authors.forename: Pedro
authors.initials: P
authors.lastname: Quelhas
authors.forename: Sarah
authors.initials: S
authors.lastname: De Jager
authors.forename: Craig
authors.initials: C
authors.lastname: Titmus
authors.forename: Aurélio
authors.initials: A
authors.lastname: Campilho
authors.forename: Hong
authors.initials: H
authors.lastname: Ren
authors.forename: Mark
authors.initials: M
authors.lastname: Estelle
authors.forename: Hong
authors.initials: H
authors.lastname: Wang
authors.forename: James A H
authors.initials: JA
authors.lastname: Murray
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000235:genetics; D016213:Cyclins / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D007210:Indoleacetic Acids / Q000494:pharmacology*; D009154:Mutation; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D018797:Cell Cycle Proteins; C486198:CycD2 protein, Arabidopsis; D016213:Cyclins; C407546:ICK2 protein, Arabidopsis; D007210:Indoleacetic Acids; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease