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Nature. 2014 Nov 6;515(7525):125-129. doi: 10.1038/nature13663. Epub 2014 Aug 24.

PLETHORA gradient formation mechanism separates auxin responses.

Author information

Institute of Biotechnology, University of Helsinki, Helsinki 00014, Finland.
Molecular Genetics, Department of Biology, Utrecht University, Utrecht 3584 CH, the Netherlands.
Department of Biosciences, University of Helsinki, Helsinki 00014, Finland.
Theoretical Biology and Bioinformatics, Utrecht University, Utrecht 3584 CH, the Netherlands.
Plant Developmental Biology, Wageningen University Research, Wageningen 6708 PB, the Netherlands.
Contributed equally


During plant growth, dividing cells in meristems must coordinate transitions from division to expansion and differentiation, thus generating three distinct developmental zones: the meristem, elongation zone and differentiation zone. Simultaneously, plants display tropisms, rapid adjustments of their direction of growth to adapt to environmental conditions. It is unclear how stable zonation is maintained during transient adjustments in growth direction. In Arabidopsis roots, many aspects of zonation are controlled by the phytohormone auxin and auxin-induced PLETHORA (PLT) transcription factors, both of which display a graded distribution with a maximum near the root tip. In addition, auxin is also pivotal for tropic responses. Here, using an iterative experimental and computational approach, we show how an interplay between auxin and PLTs controls zonation and gravitropism. We find that the PLT gradient is not a direct, proportionate readout of the auxin gradient. Rather, prolonged high auxin levels generate a narrow PLT transcription domain from which a gradient of PLT protein is subsequently generated through slow growth dilution and cell-to-cell movement. The resulting PLT levels define the location of developmental zones. In addition to slowly promoting PLT transcription, auxin also rapidly influences division, expansion and differentiation rates. We demonstrate how this specific regulatory design in which auxin cooperates with PLTs through different mechanisms and on different timescales enables both the fast tropic environmental responses and stable zonation dynamics necessary for coordinated cell differentiation.

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