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Updated: May 19, 2026

Lateral Root Inducible System in Arabidopsis and Maize
Published on: January 14, 2016
A PHABULOSA/cytokinin feedback loop controls root growth in Arabidopsis
Raffaele Dello Ioio1, Carla Galinha, Alexander G Fletcher
1Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, UK.
Abstract:
The hormone cytokinin (CK) controls root length in Arabidopsis thaliana by defining where dividing cells, derived from stem cells of the root meristem, start to differentiate [1-6]. However, the regulatory inputs directing CK to promote differentiation remain poorly understood. Here, we show that the HD-ZIPIII transcription factor PHABULOSA (PHB) directly activates the CK biosynthesis gene ISOPENTENYL TRANSFERASE 7 (IPT7), thus promoting cell differentiation and regulating root length. We further demonstrate that CK feeds back to repress both PHB and microRNA165, a negative regulator of PHB. These interactions comprise an incoherent regulatory loop in which CK represses both its activator and a repressor of its activator. We propose that this regulatory circuit determines the balance of cell division and differentiation during root development and may provide robustness against CK fluctuations.
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