title: Class I KNOX transcription factors promote differentiation of cambial derivatives into xylem fibers in the Arabidopsis hypocotyl.
abstract: The class I KNOX transcription factors SHOOT MERISTEMLESS (STM) and KNAT1 are important regulators of meristem maintenance in shoot apices, with a dual role of promoting cell proliferation and inhibiting differentiation. We examined whether they control stem cell maintenance in the cambium of Arabidopsis hypocotyls, a wood-forming lateral meristem, in a similar fashion as in the shoot apical meristem. Weak loss-of-function alleles of KNAT1 and STM led to reduced formation of xylem fibers - highly differentiated cambial derivatives - whereas cell proliferation in the cambium was only mildly affected. In a knat1;stm double mutant, xylem fiber differentiation was completely abolished, but residual cambial activity was maintained. Expression of early and late markers of xylary cell differentiation was globally reduced in the knat1;stm double mutant. KNAT1 and STM were found to act through transcriptional repression of the meristem boundary genes BLADE-ON-PETIOLE 1 (BOP1) and BOP2 on xylem fiber differentiation. Together, these data indicate that, in the cambium, KNAT1 and STM, contrary to their function in the shoot apical meristem, promote cell differentiation through repression of BOP genes.
authors.affiliation: Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå SE-901 83, Sweden.
authors.forename: Daniela
authors.initials: D
authors.lastname: Liebsch
authors.affiliation: Department of Forest Botany and Tree Physiology, University of Göttingen, Göttingen DE-37077, Germany.
authors.forename: Widi
authors.initials: W
authors.lastname: Sunaryo
authors.affiliation: Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå SE-901 83, Sweden.
authors.forename: Mattias
authors.initials: M
authors.lastname: Holmlund
authors.affiliation: Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå SE-901 83, Sweden.
authors.forename: Mikael
authors.initials: M
authors.lastname: Norberg
authors.affiliation: Institute of Biotechnology, University of Helsinki, Helsinki 00014, Finland.
authors.forename: Jing
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå SE-901 83, Sweden.
authors.forename: Hardy C
authors.initials: HC
authors.lastname: Hall
authors.affiliation: Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå SE-901 83, Sweden.
authors.forename: Hanna
authors.initials: H
authors.lastname: Helizon
authors.affiliation: Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå SE-901 83, Sweden Department of Forest Botany and Tree Physiology, University of Göttingen, Göttingen DE-37077, Germany.
authors.forename: Xu
authors.initials: X
authors.lastname: Jin
authors.affiliation: Institute of Biotechnology, University of Helsinki, Helsinki 00014, Finland.
authors.forename: Ykä
authors.initials: Y
authors.lastname: Helariutta
authors.affiliation: Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå SE-901 83, Sweden.
authors.forename: Ove
authors.initials: O
authors.lastname: Nilsson
authors.affiliation: Department of Forest Botany and Tree Physiology, University of Göttingen, Göttingen DE-37077, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Polle
authors.affiliation: Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå SE-901 83, Sweden Department of Forest Botany and Tree Physiology, University of Göttingen, Göttingen DE-37077, Germany urs.fischer@slu.se.
authors.forename: Urs
authors.initials: U
authors.lastname: Fischer
mesh_terms: D017360:Arabidopsis / Q000254:growth & development*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D058506:Cambium / Q000166:cytology; D002454:Cell Differentiation / Q000502:physiology; D049109:Cell Proliferation / Q000502:physiology; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology*; D018398:Homeodomain Proteins / Q000378:metabolism*; D018546:Hypocotyl / Q000166:cytology*; D007150:Immunohistochemistry; D018519:Meristem / Q000254:growth & development*; D060888:Real-Time Polymerase Chain Reaction; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; C496963:BOP1 protein, Arabidopsis; C506721:BOP2 protein, Arabidopsis; D018398:Homeodomain Proteins; C092212:KNAT1 protein, Arabidopsis; C097496:STM protein, Arabidopsis; D014157:Transcription Factors
keywords: Arabidopsis; Cambium; Class I KNOX transcription factors; Secondary growth; Stem cell maintenance