Cell size is determined by the duration and rate of growth and plays a central role in cell function. Root hairs are tip-growing cellular projections that emerge from the root epidermis and explore the soil to acquire nutrients and water1. Previously we demonstrated that the basic helix–loop–helix transcription factor root hair defective 6-like 4 (RSL4) is necessary and sufficient for root hair growth2. Here we show that RSL4 is synthesized in a 4-h pulse at the initiation of hair elongation and is gradually degraded by the 26S proteasome. The amount of RSL4 synthesis during this pulse is modulated as part of a root hair growth response to low phosphate. RSL4 synthesis increases in low phosphate and this increase prolongs the growth phase, resulting in the development of long root hairs. Our data demonstrate that the amount of RSL4 synthesized during the pulse directly determines the final size of the differentiated root hair cell. We propose that the modulation of growth-promoting transcription factors by external cues could be a general mechanism for the regulation of cell growth by environmental factors during development.
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We thank M. Pernas-Ochoa, B. Catarino, S. Honkanen, V. Jones, H. Breuninger, T. Tam and J. Agusti for critically reading the manuscript. We acknowledge the help of I. Moore and M. Fricker with confocal microscopy. This research was funded by EMBO LTF (ALTF 817-2008) and EU Marie Curie FP7-PEOPLE-IEF-2008 (Project number-236802) grants (to S.D.) and ERC (European Research Council Advanced Grant EVO500, Project No: 25028) and BBSRC (BBG0198941) grants (to L.D.).
The authors declare no competing financial interests.
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Datta, S., Prescott, H. & Dolan, L. Intensity of a pulse of RSL4 transcription factor synthesis determines Arabidopsis root hair cell size. Nature Plants 1, 15138 (2015). https://doi.org/10.1038/nplants.2015.138
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