title: Enhancement of secondary xylem cell proliferation by Arabidopsis                      cyclin D overexpression in tobacco plants.
abstract: Secondary xylem is composed of daughter cells produced by the vascular cambium in the stem. Cell proliferation of the secondary xylem is the result of long-range cell division in the vascular cambium. Most xylem cells have a thickened secondary cell wall, representing a large amount of biomass storage. Therefore, regulation of cell division in the vascular cambium and differentiation into secondary xylem is important for biomass production. Cell division is regulated by cell cycle regulators. In this study, we confirm that cell cycle regulators influence cell division in the vascular cambium in tobacco. We produced transgenic tobacco that expresses Arabidopsis thaliana cyclin D2;1 (AtcycD2;1) and AtE2Fa-DPa under the control of the CaMV35S promoter. Each gene is a positive regulator of the cell cycle, and is known to influence the transition from G1 phase to S phase. AtcycD2;1-overexpressing tobacco had more secondary xylem cells when compared with control plants. In order to evaluate cell division activity in the vascular cambium, we prepared a Populus trichocarpa cycB1;1 (PtcycB1;1) promoter containing a destruction box motif for ubiquitination and a β-glucuronidase-encoding gene (PtcycB1;1pro:GUS). In transgenic tobacco containing PtcycB1;1pro:GUS, GUS staining was specifically observed in meristem tissues, such as the root apical meristem and vascular cambium. In addition, mitosis-monitoring plants containing AtcycD2;1 had stronger GUS staining in the cambium when compared with control plants. Our results indicated that overexpression of AtcycD enhances cell division in the vascular cambium and increases secondary xylem differentiation in tobacco.
  
  
  CONCLUSIONS
  We succeeded in inducing cell proliferation of cambium and enlargement of secondary xylem region by AtcycD overexpression. We also evaluated mitotic activity in cambium using cyclin-GUS fusion protein from poplar.
authors.affiliation: Graduate School of Bio-Applications and Systems Engineering, Tokyo University of Agriculture and Technology, Tokyo, 184-8588, Japan.
authors.forename: Takeo
authors.initials: T
authors.lastname: Fujii
authors.forename: Kanna
authors.initials: K
authors.lastname: Sato
authors.forename: Noriko
authors.initials: N
authors.lastname: Matsui
authors.forename: Takayuki
authors.initials: T
authors.lastname: Furuichi
authors.forename: Sachi
authors.initials: S
authors.lastname: Takenouchi
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Nishikubo
authors.forename: Yuzo
authors.initials: Y
authors.lastname: Suzuki
authors.forename: Shinya
authors.initials: S
authors.lastname: Kawai
authors.forename: Taku
authors.initials: T
authors.lastname: Demura
authors.forename: Shinya
authors.initials: S
authors.lastname: Kajita
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Katayama
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D058506:Cambium / Q000166:cytology / Q000378:metabolism; D049109:Cell Proliferation; D016213:Cyclins / Q000235:genetics / Q000378:metabolism*; D050684:E2F Transcription Factors / Q000235:genetics / Q000378:metabolism; D016193:G1 Phase; D018506:Gene Expression Regulation, Plant; D005966:Glucuronidase / Q000378:metabolism; D008938:Mitosis; D018547:Plant Stems / Q000166:cytology / Q000378:metabolism; D058526:Plant Vascular Bundle / Q000166:cytology / Q000378:metabolism; D030821:Plants, Genetically Modified; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016196:S Phase; D013194:Staining and Labeling; D014026:Nicotiana / Q000166:cytology* / Q000235:genetics*; D014162:Transfection; D052584:Xylem / Q000166:cytology* / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C486198:CycD2 protein, Arabidopsis; D016213:Cyclins; D050684:E2F Transcription Factors; C496141:E2Fa protein, Arabidopsis; D005966:Glucuronidase