title: LBD29 regulates the cell cycle progression in response to auxin during lateral root formation in Arabidopsis thaliana.
abstract: OBJECTIVE
  LATERAL ORGAN BOUNDARIES DOMAIN 29 (LBD29), an important molecule downstream of auxin response factors ARF7 and ARF19, has a critical role in lateral root formation in Arabidopsis thaliana. The cell cycle activation of pericycle cells and their speciﬁcation triggered by auxin are crucial for the initiation of lateral roots. In this study, we attempted to determine whether LBD29 is involved in auxin signalling and/or cell cycle regulation and to characterize the roles of LBD29 in these processes.
  
  
  METHODS
  The impact of LBD29 on cell cycling progression in pericycle cells was investigated in lbd29 loss-of-function mutant or LBD29-over-expressing plants. The cell cycle was determined by measuring the expression of some cell cycle-related genes using in situ hybridization and quantitative real-time reverse transcription-PCR (qRT-PCR). Furthermore, the cell division in the root explants from either the lbd29 mutant, LBD29-over-expressing plants or the wild type grown in auxin-rich media was also analysed and compared by the distribution of DR5:β-glucuronidase (GUS) in the primordia or by the expression of PIN-FORMED (PIN) members and PLETHROA 1 (PLT1) which represented the auxin response by the pericycle cells.
  
  
  RESULTS
  lbd29 mutation resulted in reduced numbers of lateral roots and primordia, whereas LBD29 over-expression resulted in more lateral root and primordia formation than in the wild type. More importantly, the level of LBD29 expression was found to be positively correlated with the level of expression of cell cycle-related genes and correlated with the numbers of subcellular organelles found in pericycle cells in the maturation zone. In addition, an in vitro experiment using root explants demonstrated that the presence of LBD29 was required for the maintenance of the cell division capacity of the pericycle. Furthermore, LBD29 appeared to modify PIN-dependent auxin signalling in the primordia since there was a correlated association between the expression of PINs, PLT1 and DR5:GUS and the expression of LBD29.
  
  
  CONCLUSIONS
  The ability of LBD29 to regulate lateral root initiation is associated with its maintenance of the cell division capacity of the pericycle in response to auxin and its involvement in the auxin signalling pathway.
authors.affiliation: Department of Molecular and Cell Biology, School of Life Science and Technology, Tongji University, Shanghai, China.
authors.forename: Zhenhua
authors.initials: Z
authors.lastname: Feng
authors.forename: Xudong
authors.initials: X
authors.lastname: Sun
authors.forename: Guangchao
authors.initials: G
authors.lastname: Wang
authors.forename: Hailiang
authors.initials: H
authors.lastname: Liu
authors.forename: Jian
authors.initials: J
authors.lastname: Zhu
mesh_terms: D017360:Arabidopsis / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000235:genetics; D007210:Indoleacetic Acids / Q000494:pharmacology*; D018517:Plant Roots / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids