Strigolactones suppress adventitious rooting in Arabidopsis and pea.

Amanda Rasmussen,Javier Agusti,Philip B Brewer,Silvia Herold,Thomas Greb,Sofie Goormachtig,Christine Anne Beveridge,Tom Beeckman,Danny Geelen,Carolien De Cuyper,Michael Glenn Mason

doi:10.1104/pp.111.187104

Abstract

Adventitious root formation is essential for the propagation of many commercially important plant species and involves the formation of roots from nonroot tissues such as stems or leaves. Here, we demonstrate that the plant hormone strigolactone suppresses adventitious root formation in Arabidopsis (Arabidopsis thaliana) and pea (Pisum sativum). Strigolactone-deficient and response mutants of both species have enhanced adventitious rooting. CYCLIN B1 expression, an early marker for the initiation of adventitious root primordia in Arabidopsis, is enhanced in more axillary growth2 (max2), a strigolactone response mutant, suggesting that strigolactones restrain the number of adventitious roots by inhibiting the very first formative divisions of the founder cells. Strigolactones and cytokinins appear to act independently to suppress adventitious rooting, as cytokinin mutants are strigolactone responsive and strigolactone mutants are cytokinin responsive. In contrast, the interaction between the strigolactone and auxin signaling pathways in regulating adventitious rooting appears to be more complex. Strigolactone can at least partially revert the stimulatory effect of auxin on adventitious rooting, and auxin can further increase the number of adventitious roots in max mutants. We present a model depicting the interaction of strigolactones, cytokinins, and auxin in regulating adventitious root formation.

Highlights

Adventitious root formation is essential for the propagation of many commercially important plant species and involves the formation of roots from nonroot tissues such as stems or leaves
To assess whether strigolactones have a role in regulating adventitious root formation, Arabidopsis mutants with defects in strigolactone synthesis or response were grown in the adventitious root induction assay using 4 d of etiolation followed by transfer to the light
We have previously shown that pea and Arabidopsis strigolactone mutants have decreased cytokinin levels in the xylem (Beveridge et al, 1997a, 1997b; Foo et al, 2007), which could potentially explain the increased adventitious rooting observed in these mutants

Summary

Introduction

Adventitious root formation is essential for the propagation of many commercially important plant species and involves the formation of roots from nonroot tissues such as stems or leaves. Indirect root formation involves the production of callus tissue prior to adventitious root development and is different from lateral root formation because the earliest events include divisions from cambium and cambium-associated cells, while lateral root formation occurs from the pericycle This type of adventitious rooting is most commonly found where roots form from stem cuttings (Goldfarb et al, 1998). It is plausible that this lowered cytokinin level may form part of the signal to the cutting that new roots are needed This idea is supported experimentally, because treatment with exogenous cytokinins results in strong suppression of adventitious root formation (Bollmark and Eliasson, 1986; De Klerk et al, 2001). These results demonstrate a role for cytokinin in negatively regulating adventitious root formation

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