title: Arabidopsis brassinosteroid biosynthetic mutant dwarf7-1 exhibits slower rates of cell division and shoot induction.
abstract: BACKGROUND
  Plant growth depends on both cell division and cell expansion. Plant hormones, including brassinosteroids (BRs), are central to the control of these two cellular processes. Despite clear evidence that BRs regulate cell elongation, their roles in cell division have remained elusive.
  
  
  RESULTS
  Here, we report results emphasizing the importance of BRs in cell division. An Arabidopsis BR biosynthetic mutant, dwarf7-1, displayed various characteristics attributable to slower cell division rates. We found that the DWARF4 gene which encodes for an enzyme catalyzing a rate-determining step in the BR biosynthetic pathways, is highly expressed in the actively dividing callus, suggesting that BR biosynthesis is necessary for dividing cells. Furthermore, dwf7-1 showed noticeably slower rates of callus growth and shoot induction relative to wild-type control. Flow cytometric analyses of the nuclei derived from either calli or intact roots revealed that the cell division index, which was represented as the ratio of cells at the G2/M vs. G1 phases, was smaller in dwf7-1 plants. Finally, we found that the expression levels of the genes involved in cell division and shoot induction, such as PROLIFERATING CELL NUCLEAR ANTIGEN2 (PCNA2) and ENHANCER OF SHOOT REGENERATION2 (ESR2), were also lower in dwf7-1 as compared with wild type.
  
  
  CONCLUSIONS
  Taken together, results of callus induction, shoot regeneration, flow cytometry, and semi-quantitative RT-PCR analysis suggest that BRs play important roles in both cell division and cell differentiation in Arabidopsis.
authors.affiliation: School of Biological Sciences, College of Natural Sciences, Seoul National University, Seoul 151-747, Korea.
authors.forename: Jinyeong
authors.initials: J
authors.lastname: Cheon
authors.forename: So-Young
authors.initials: SY
authors.lastname: Park
authors.forename: Burkhard
authors.initials: B
authors.lastname: Schulz
authors.forename: Sunghwa
authors.initials: S
authors.lastname: Choe
mesh_terms: D017360:Arabidopsis / Q000166:cytology* / Q000235:genetics / Q000378:metabolism; D053898:Biosynthetic Pathways; D060406:Brassinosteroids; D002454:Cell Differentiation; D002455:Cell Division; D002777:Cholestanols / Q000378:metabolism*; D005434:Flow Cytometry; D009154:Mutation; D018520:Plant Shoots / Q000166:cytology* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013260:Steroids, Heterocyclic / Q000378:metabolism*
chemical_list: D060406:Brassinosteroids; D002777:Cholestanols; D013260:Steroids, Heterocyclic; C023623:brassinolide