Root, shoot, and lateral meristems are the main regions of cell proliferation in plants. It has been proposed that meristems might have evolved dedicated transcriptional networks to balance cell proliferation. Here, we show that basic helix-loop-helix (bHLH) transcription factor heterodimers formed by members of the TARGET OF MONOPTEROS5 (TMO5) and LONESOME HIGHWAY (LHW) subclades are general regulators of cell proliferation in all meristems. Yet, genetics and expression analyses suggest specific functions of these transcription factors in distinct meristems, possibly due to their expression domains determining heterodimer complex variations within meristems, and to a certain extent to the absence of some of them in a given meristem. Target gene specificity analysis for heterodimer complexes focusing on the LONELY GUY gene targets further suggests differences in transcriptional responses through heterodimer diversification that could allow a common bHLH heterodimer complex module to contribute to cell proliferation control in multiple meristems.

Functional Genomics and Proteomics National Centre for Biomolecular Research Faculty of Science and Plant Sciences Core Facility Mendel Centre for Plant Genomics and Proteomics Central European Institute of Technology Masaryk University 62500 Brno Czechia

Ghent University Department of Plant Biotechnology and Bioinformatics Technologiepark 71 9052 Ghent Belgium

Institute of Synthetic Biology and CEPLAS Heinrich Heine Universität Düsseldorf Universitätsstrasse 1 40225 Düsseldorf Germany

Laboratoire Reproduction et Développement des Plantes University Lyon ENS de Lyon CNRS INRAE INRIA 69342 Lyon France

VIB Centre for Plant Systems Biology Technologiepark 71 9052 Ghent Belgium

ZMBP Center for Plant Molecular Biology University of Tübingen Auf der Morgenstelle 32 72076 Tübingen Germany

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Cytokinins - regulators of de novo shoot organogenesis