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Published on April 24, 2009; 10.1104/pp.109.137505

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Received February 20, 2009
Accepted April 20, 2009

The cytokinin type-B response regulator PtRR13 is a negative regulator of adventitious root development in Populus

Gustavo A. Ramirez-Carvajal , Alison M. Morse , Christopher Dervinis , and John M. Davis *

Plant Molecular and Cellular Biology Program, University of Florida, PO Box 110690, Gainesville FL 32611, USA; School of Forest Resources and Conservation, University of Florida, PO Box 110410, Gainesville FL 32611, USA

* Corresponding author; email: jmdavis{at}ufl.edu.

Adventitious root formation at the base of plant cuttings is an innate de novo organogenesis process that allows massive vegetative propagation of many economically and ecologically important species. The early molecular events following shoot excision are not well understood. Using whole-genome microarrays, we detected significant transcriptome remodeling during 48 hours following shoot removal in Populus tremula x Populus alba softwood cuttings in the absence of exogenous auxin, with 27% and 36% of the gene models showing differential abundance between 0 and 6 hours, and 6 and 24 hours, respectively. During these two time intervals, gene networks involved in protein turnover, protein phosphorylation, molecular transport and translation were among the most significantly regulated. Transgenic lines expressing a constitutively active form of the Populus type-B cytokinin response regulator PtRR13 ({Delta}DDKPtRR13) have a delayed rooting phenotype and cause misregulation of COV1, a negative regulator of vascularization; PDR9, an auxin efflux transporter; and two AP2/ERF genes with sequence similarity to TINY. Inappropriate cytokinin action via {Delta}DDKPtRR13 expression appeared to disrupt adventitious root development 24 hours after shoot excision, when root founder cells are hypothesized to be sensitive to the negative effects of cytokinin. Our results are consistent with PtRR13 acting downstream of cytokinin to repress adventitious root formation in intact plants, and that reduced cytokinin signaling after shoot excision enables coordinated expression of ethylene, auxin and vascularization pathways leading to adventitious root development.






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