Analysis of theDECREASED APICAL DOMINANCEGenes of Petunia in the Control of Axillary Branching

Abstract

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 characterization, 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 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 reverse transcription-polymerase chain reaction 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 because 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.Determination of aerial growth patterns and architecture is an important developmental process within a plant. Control of the type, position, and timing of shoot growth allows plants to develop in a dynamic manner that is defined genetically, but modulated environmentally (Bell, 1991). Patterns of plant branching are diverse and despite the importance of branching in plant development, and many years of study, the controls of lateral branching are still not fully understood (Napoli et al., 1999;Angenent et al., 2005;Beveridge, 2006).One approach to studying branching is the induction of mutations in endogenous genes. A group of relatively nonpleiotropic mutants that cause increased lateral branching in plants has been identified in several species. These include the decreased apical dominance (dad) mutants of petunia

Mutagenesis in Petunia x hybrida Vilm. and isolation of a novel morphological mutant

“…Although the association between auxin and trichome development remains unclear in Arabidopsis (Hülskamp et al, 2004), it has been established for tomato, cotton and other species (Serna and Martin, 2006;Lee et al, 2007). Patterns of plant branching and organ formation are diverse and still not fully understood (Angenent et al, 2005;Beveridge, 2006) and a series of petunia mutants has helped to uncover the genetic control of higher plant branching patterns (Napoli and Ruehle, 1996;Simons et al, 2007). The phenotypes of the novel mutant wad suggest that it will provide further comparison tools for the investigation of branching control and developmental growth regulation in plants.…”

“…Recently, with the completion of several genome and EST projects, the amount of sequence data has increased drastically and allowed the effective use of mutant populations to investigate gene function in high-throughput reverse genetic approaches (Alonso and Ecker, 2006). In petunia, gene function studies have profited from the endogenous system of transposable elements (van den Broeck et al, 1998) to characterize the genetic determinants of a wide range of biological processes (Baumann et al, 2007;Cartolano et al, 2007;Simons et al, 2007). Although highly effective, transposon tagging employing non-engineered sequences can only generate loss-of-function mutations and the unstable nature of the insertion may impair long-term genetic analyses (Alonso and Ecker, 2006).…”

The BUD2 mutation affects plant architecture through altering cytokinin and auxin responses in Arabidopsis

“…Recent studies on a series of branching mutants, such as more axillary growth (max) of Arabidopsis [37][38][39][40], ramosus (rms) mutants of pea [41][42][43], decreased apical dominance (dad) mutants of petunia [44,45] and dwarf (d) mutants of rice [46][47][48][49][50][51], have revealed strigolactone as a second messenger of auxin action on the control of AM outgrowth [52,53]. Strigolactones, a group of terpenoid lactones that have been found in root exudates of diverse plant species, are synthesized from carotenoids in roots and transported acropetally or synthesized locally to repress the outgrowth of shoot branches [38,[54][55][56].…”

Inhibition of Tiller Bud Outgrowth in thetinMutant of Wheat Is Associated with Precocious Internode Development

“…Analyses of the highly branched ramosus (rms) mutants of pea and the decreased apical dominance (dad) mutant of petunia (Petunia hybrida) led to the discovery of another hormone-like signal known as shoot multiplication signal (SMS) that inhibits bud outgrowth in response to auxin (Napoli, 1996;Beveridge et al, 1997;Beveridge et al, 2000;Beveridge, 2006). The identification of a series of branching mutants in Arabidopsis (Arabidopsis thaliana) known as max (for more axillary growth) and cloning of the MAX genes (Stirnberg et al, 2002;Sorefan et al, 2003;Booker et al, 2004;Booker et al, 2005), as well as related genes from pea (Sorefan et al, 2003;Johnson et al, 2006), rice (Oryza sativa; Ishikawa et al, 2005;Zou et al, 2006;Arite et al, 2007), and petunia (Snowden et al, 2005;Simons et al, 2007) led to the discovery that the SMS signal is a new hormone, strigolactone (Gomez-Roldan et al, 2008;Umehara et al, 2008). Therefore, apical dominance in annuals is regulated by auxin, cytokinin, and strigolactones and their interactions (Beveridge et al, 2009;Domagalska and Leyser, 2011).…”