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Curr Biol. 2019 Apr 1;29(7):1199-1205.e4. doi: 10.1016/j.cub.2019.02.022. Epub 2019 Mar 14.

The Lateral Root Cap Acts as an Auxin Sink that Controls Meristem Size.

Author information

1
Department of Biology, University of Pisa - via L. Ghini, 13 - 56126 Pisa, Italy. Electronic address: riccardo.dimambro@unipi.it.
2
Dipartimento di Biologia e Biotecnologie, Laboratory of Functional Genomics and Proteomics of Model Systems, Università di Roma, Sapienza - via dei Sardi, 70 - 00185 Rome, Italy.
3
Istituto di Biologia e Biotecnologia Agraria, Consiglio Nazionale delle Ricerche - Via Alfonso Corti, 12 - 20133 Milano, Italy.
4
Department of Plant and Microbial Biology, North Carolina State University, Raleigh, NC, United States.
5
Department of Biology and Howard Hughes Medical Institute, Duke University, Durham, NC 27708, USA.
6
Plant Molecular and Cellular Biology Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
7
Dipartimento di Biologia e Biotecnologie, Laboratory of Functional Genomics and Proteomics of Model Systems, Università di Roma, Sapienza - via dei Sardi, 70 - 00185 Rome, Italy. Electronic address: sabrina.sabatini@uniroma1.it.

Abstract

Plant developmental plasticity relies on the activities of meristems, regions where stem cells continuously produce new cells [1]. The lateral root cap (LRC) is the outermost tissue of the root meristem [1], and it is known to play an important role during root development [2-6]. In particular, it has been shown that mechanical or genetic ablation of LRC cells affect meristem size [7, 8]; however, the molecular mechanisms involved are unknown. Root meristem size and, consequently, root growth depend on the position of the transition zone (TZ), a boundary that separates dividing from differentiating cells [9, 10]. The interaction of two phytohormones, cytokinin and auxin, is fundamental in controlling the position of the TZ [9, 10]. Cytokinin via the ARABIDOPSIS RESPONSE REGULATOR 1 (ARR1) control auxin distribution within the meristem, generating an instructive auxin minimum that positions the TZ [10]. We identify a cytokinin-dependent molecular mechanism that acts in the LRC to control the position of the TZ and meristem size. We show that auxin levels within the LRC cells depends on PIN-FORMED 5 (PIN5), a cytokinin-activated intracellular transporter that pumps auxin from the cytoplasm into the endoplasmic reticulum, and on irreversible auxin conjugation mediated by the IAA-amino synthase GRETCHEN HAGEN 3.17 (GH3.17). By titrating auxin in the LRC, the PIN5 and the GH3.17 genes control auxin levels in the entire root meristem. Overall, our results indicate that the LRC serves as an auxin sink that, under the control of cytokinin, regulates meristem size and root growth.

KEYWORDS:

auxin; cell differentiation; cell division; cytokinin; developmental boundary; organ growth; root meristem

PMID:
30880016
DOI:
10.1016/j.cub.2019.02.022

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