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Postmitotic cell growth defines cell shape and size during development. However, the mechanisms regulating postmitotic cell growth in plants remain unknown. Here we report the discovery of a basic helix-loop-helix (bHLH) transcription factor called RSL4 (ROOT HAIR DEFECTIVE 6-LIKE 4) that is sufficient to promote postmitotic cell growth in Arabidopsis thaliana root-hair cells. Loss of RSL4 function resulted in the development of very short root hairs. In contrast, constitutive RSL4 expression programmed constitutive growth, resulting in the formation of very long root hairs. Hair-cell growth signals, such as auxin and low phosphate availability, modulate hair cell extension by regulating RSL4 transcript and protein levels. RSL4 is thus a regulator of growth that integrates endogenous developmental and exogenous environmental signals that together control postmitotic growth in root hairs. The control of postmitotic growth by transcription factors may represent a general mechanism for regulating cell size across diverse organisms.

Original publication




Journal article


Nat Genet

Publication Date





264 - 267


Arabidopsis, Arabidopsis Proteins, Basic Helix-Loop-Helix Transcription Factors, Cell Proliferation, Cell Size, Cycloheximide, Dexamethasone, Gene Expression Regulation, Developmental, Gene Expression Regulation, Plant, Indoleacetic Acids, Plant Growth Regulators, Plant Roots, Plants, Genetically Modified, Protein Synthesis Inhibitors