title: Arabidopsis thaliana homeobox 12 (ATHB12), a homeodomain-leucine zipper protein, regulates leaf growth by promoting cell expansion and endoreduplication.
abstract: Arabidopsis thaliana homeobox 12 (ATHB12), a homeodomain-leucine zipper class I (HD-Zip I) gene, is highly expressed in leaves and stems, and induced by abiotic stresses, but its role in development remains obscure. To understand its function during plant development, we studied the effects of loss and gain of function. Expression of ATHB12 fused to the EAR-motif repression domain (SRDX) - P35 S ::ATHB12SRDX (A12SRDX) and PATHB 12 ::ATHB12SRDX - slowed both leaf and root growth, while the growth of ATHB12-overexpressing seedlings (A12OX) was accelerated. Microscopic examination revealed changes in the size and number of leaf cells. Ploidy was reduced in A12SRDX plants, accompanied by decreased cell expansion and increased cell numbers. By contrast, cell size was increased in A12OX plants, along with increased ploidy and elevated expression of cell cycle switch 52s (CCS52s), which are positive regulators of endoreduplication, indicating that ATHB12 promotes leaf cell expansion and endoreduplication. Overexpression of ATHB12 led to decreased phosphorylation of Arabidopsis thaliana ribosomal protein S6 (AtRPS6), a regulator of cell growth. In addition, induction of ATHB12 in the presence of cycloheximide increased the expression of several genes related to cell expansion, such as EXPANSIN A10 (EXPA10) and DWARF4 (DWF4). Our findings strongly suggest that ATHB12 acts as a positive regulator of endoreduplication and cell growth during leaf development.
authors.affiliation: Department of Biological Science, Sookmyung Women's University, Seoul, 140-742, Korea.
authors.forename: Yoon-Sun
authors.initials: YS
authors.lastname: Hur
authors.forename: Ji-Hyun
authors.initials: JH
authors.lastname: Um
authors.forename: Sunghan
authors.initials: S
authors.lastname: Kim
authors.forename: Kyunga
authors.initials: K
authors.lastname: Kim
authors.forename: Hee-Jung
authors.initials: HJ
authors.lastname: Park
authors.forename: Jong-Seok
authors.initials: JS
authors.lastname: Lim
authors.forename: Woo-Young
authors.initials: WY
authors.lastname: Kim
authors.forename: Sang Eun
authors.initials: SE
authors.lastname: Jun
authors.forename: Eun Kyung
authors.initials: EK
authors.lastname: Yoon
authors.forename: Jun
authors.initials: J
authors.lastname: Lim
authors.forename: Masaru
authors.initials: M
authors.lastname: Ohme-Takagi
authors.forename: Donggiun
authors.initials: D
authors.lastname: Kim
authors.forename: Jongbum
authors.initials: J
authors.lastname: Park
authors.forename: Gyung-Tae
authors.initials: GT
authors.lastname: Kim
authors.forename: Choong-Ill
authors.initials: CI
authors.lastname: Cheon
mesh_terms: D017360:Arabidopsis / Q000166:cytology / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D048430:Cell Shape / Q000187:drug effects; D002473:Cell Wall / Q000187:drug effects / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D062951:Endoreduplication / Q000187:drug effects; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D016350:Leucine Zippers; D010641:Phenotype; D010766:Phosphorylation / Q000187:drug effects; D018515:Plant Leaves / Q000166:cytology* / Q000187:drug effects / Q000254:growth & development*; D018517:Plant Roots / Q000166:cytology / Q000187:drug effects / Q000254:growth & development; D030821:Plants, Genetically Modified; D011003:Ploidies
chemical_list: D029681:Arabidopsis Proteins; C000594519:AtHB12 protein, Arabidopsis; D018744:DNA, Plant; D018398:Homeodomain Proteins; C543707:RPS6 protein, Arabidopsis
keywords: Arabidopsis thaliana homeobox 12 (ATHB12); cell expansion; endoreduplication; homeobox; leaf development