title: A Negative Feedback Loop Controlling bHLH Complexes Is Involved in Vascular Cell Division and Differentiation in the Root Apical Meristem.
abstract: Controlling cell division and differentiation in meristems is essential for proper plant growth. Two bHLH heterodimers consisting of LONESOME HIGHWAY (LHW) and TARGET OF MONOPTEROS 5 (TMO5)/TMO5-LIKE1 (T5L1) regulate periclinal cell division in vascular cells in the root apical meristem (RAM). In this study, we further investigated the functions of LHW-T5L1, finding that in addition to controlling cell division, this complex regulates xylem differentiation in the RAM via a novel negative regulatory system. LHW-T5L1 upregulated the thermospermine synthase gene ACAULIS5 (ACL5), as well as SUPPRESSOR OF ACAULIS5 LIKE3 (SACL3), which encodes a bHLH protein, in the RAM. The SACL3 promoter sequence contains a conserved upstream open reading frame (uORF), which blocked translation of the main SACL3 ORF in the absence of thermospermine. Thermospermine eliminated the negative effect of uORF and enhanced SACL3 production. Further genetic and molecular biological analyses indicated that ACL5 and SACL3 suppress the function of LHW-T5L1 through a protein-protein interaction between LHW and SACL3. Finally, we showed that a negative feedback loop consisting of LHW-T5L1, ACL5, SACL3, and LHW-SACL3 contributes to maintain RAM size and proper root growth. These findings suggest that a negative feedback loop regulates the LHW-T5L1 output level to coordinate cell division and differentiation in a cell-autonomous manner.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Katayama
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Kuninori
authors.initials: K
authors.lastname: Iwamoto
authors.affiliation: School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka 422-8526, Japan.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Kariya
authors.affiliation: School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka 422-8526, Japan.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Asakawa
authors.affiliation: School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka 422-8526, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Kan
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. Electronic address: fukuda@bs.s.u-tokyo.ac.jp.
authors.forename: Hiroo
authors.initials: H
authors.lastname: Fukuda
authors.affiliation: Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. Electronic address: kyoko@bs.s.u-tokyo.ac.jp.
authors.forename: Kyoko
authors.initials: K
authors.lastname: Ohashi-Ito
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics* / Q000378:metabolism; D002454:Cell Differentiation; D002455:Cell Division; D018506:Gene Expression Regulation, Plant; D018519:Meristem / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D052584:Xylem / Q000235:genetics / Q000254:growth & development / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins