Received August 3, 2006
Accepted November 29, 2006
Analysis of the DECREASED APICAL DOMINANCE (DAD) Genes of Petunia hybrida in the Control of Axillary Branching
Joanne L. Simons , Carolyn A. Napoli , Bart J Janssen , Kim M Plummer , and Kimberley C Snowden *
HortResearch, Private Bag 92169, Mt Albert, Auckland, New Zealand
Department of Plant Sciences, University of Arizona, Tucson, AZ 85721-0036, USA
School of Biological Sciences, University of Auckland, Auckland, New Zealand
* Corresponding author; email: ksnowden{at}hortresearch.co.nz.
The control of branch development is a major determinant of architecture in plants. Branching in petunia (Petunia hybrida) is controlled by the DECREASED APICAL DOMINANCE (DAD) genes. Gene functions were investigated by plant grafting, morphology studies, double mutant characterisation and gene expression analysis. Both dad1-1 and dad3 increased branching mutants can be reverted to a near wild-type phenotype by grafting to a wild-type or to a dad2 mutant root stock, indicating that both genes affect the production of a graft transmissible substance that controls branching. Expression of the DAD1 gene in the stems of grafted plants, detected by quantitative RT-PCR, correlates with the branching phenotype of the plants. The dad2-1 mutant cannot be reverted by grafting, indicating that this gene acts predominantly in the shoot of the plant. Double mutant analysis indicates that the DAD2 gene acts in the same pathway as the DAD1 and DAD3 genes as the dad1-1dad2-1 and dad2-1dad3 double mutants are indistinguishable from the dad2-1 mutant. However, the dad1-1dad3 double mutant has an additive phenotype, with decreased height of the plants, delayed flowering and reduced germination rates compared to the single mutants. This result, together with the observation that the dad1-1 and dad3 mutants cannot be reverted by grafting to each other, suggests that the DAD1 and DAD3 genes act in the same pathway, but not in a simple stepwise fashion.
