A PHABULOSA/cytokinin feedback loop controls root growth in Arabidopsis.
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.
Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, UK.
Raffaele
R
Dello Ioio
Carla
C
Galinha
Alexander G
AG
Fletcher
Stephen P
SP
Grigg
Attila
A
Molnar
Viola
V
Willemsen
Ben
B
Scheres
Sabrina
S
Sabatini
David
D
Baulcombe
Philip K
PK
Maini
Miltos
M
Tsiantis
D019883:Alkyl and Aryl Transferases / Q000235:genetics* / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D002454:Cell Differentiation; D002455:Cell Division; D003583:Cytokinins / Q000235:genetics / Q000378:metabolism*; D025461:Feedback, Physiological; D018506:Gene Expression Regulation, Plant; D018398:Homeodomain Proteins / Q000378:metabolism*; D018519:Meristem / Q000166:cytology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000254:growth & development* / Q000378:metabolism; D015398:Signal Transduction
D029681:Arabidopsis Proteins; D003583:Cytokinins; D018398:Homeodomain Proteins; D035683:MicroRNAs; C114647:PHB protein, Arabidopsis; D019883:Alkyl and Aryl Transferases; C024274:adenylate isopentenyltransferase