Cytokinins act directly on lateral root founder cells to inhibit root initiation.
In Arabidopsis thaliana, lateral roots are formed from root pericycle cells adjacent to the xylem poles. Lateral root development is regulated antagonistically by the plant hormones auxin and cytokinin. While a great deal is known about how auxin promotes lateral root development, the mechanism of cytokinin repression is still unclear. Elevating cytokinin levels was observed to disrupt lateral root initiation and the regular pattern of divisions that characterizes lateral root development in Arabidopsis. To identify the stage of lateral root development that is sensitive to cytokinins, we targeted the expression of the Agrobacterium tumefaciens cytokinin biosynthesis enzyme isopentenyltransferase to either xylem-pole pericycle cells or young lateral root primordia using GAL4-GFP enhancer trap lines. Transactivation experiments revealed that xylem-pole pericycle cells are sensitive to cytokinins, whereas young lateral root primordia are not. This effect is physiologically significant because transactivation of the Arabidopsis cytokinin degrading enzyme cytokinin oxidase 1 in lateral root founder cells results in increased lateral root formation. We observed that cytokinins perturb the expression of PIN genes in lateral root founder cells and prevent the formation of an auxin gradient that is required to pattern lateral root primordia.
Institut de Recherche pour le Développement, Unité Mixte de Recherche Diversité et Adaptation des Plantes Cultivées, Agro.M, Université Montpellier 2, Equipe Rhizogenèse, France. laplaze@mpl.ird.fr
Laurent
L
Laplaze
Eva
E
Benkova
Ilda
I
Casimiro
Lies
L
Maes
Steffen
S
Vanneste
Ranjan
R
Swarup
Dolf
D
Weijers
Vanessa
V
Calvo
Boris
B
Parizot
Maria Begoña
MB
Herrera-Rodriguez
Remko
R
Offringa
Neil
N
Graham
Patrick
P
Doumas
Jiri
J
Friml
Didier
D
Bogusz
Tom
T
Beeckman
Malcolm
M
Bennett
D016960:Agrobacterium tumefaciens / Q000235:genetics; D019883:Alkyl and Aryl Transferases / Q000235:genetics / Q000378:metabolism; D017360:Arabidopsis / Q000187:drug effects* / Q000196:embryology / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001593:Benzyl Compounds; D003583:Cytokinins / Q000494:pharmacology*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D007210:Indoleacetic Acids / Q000494:pharmacology; D007701:Kinetin / Q000494:pharmacology; D008954:Models, Biological; D018517:Plant Roots / Q000187:drug effects* / Q000196:embryology / Q000235:genetics; D030821:Plants, Genetically Modified; D011687:Purines; D020133:Reverse Transcriptase Polymerase Chain Reaction; D052584:Xylem / Q000235:genetics / Q000378:metabolism
D029681:Arabidopsis Proteins; D001593:Benzyl Compounds; D003583:Cytokinins; D007210:Indoleacetic Acids; D011687:Purines; D019883:Alkyl and Aryl Transferases; C024274:adenylate isopentenyltransferase; C480551:benzylaminopurine; D007701:Kinetin