Abstract
Commercial carnation (Dianthus caryophyllus) cultivars are vegetatively propagated from axillary stem cuttings through adventitious rooting; a process which is affected by complex interactions between nutrient and hormone levels and is strongly genotype-dependent. To deepen our understanding of the regulatory events controlling this process, we performed a comparative study of adventitious root (AR) formation in two carnation cultivars with contrasting rooting performance, “2101–02 MFR” and “2003 R 8”, as well as in the reference cultivar “Master”. We provided molecular evidence that localized auxin response in the stem cutting base was required for efficient adventitious rooting in this species, which was dynamically established by polar auxin transport from the leaves. In turn, the bad-rooting behavior of the “2003 R 8” cultivar was correlated with enhanced synthesis of indole-3-acetic acid conjugated to aspartic acid by GH3 proteins in the stem cutting base. Treatment of stem cuttings with a competitive inhibitor of GH3 enzyme activity significantly improved rooting of “2003 R 8”. Our results allowed us to propose a working model where endogenous auxin homeostasis regulated by GH3 proteins accounts for the cultivar dependency of AR formation in carnation stem cuttings.
Highlights
New carnation (Dianthus caryophyllus) cultivars are mainly bred for traits affecting flower morphology, such as flower size, petal shape, petal number, flower color, and flower vase-life among others, as well as for traits improving plant production and pathogen resistance (Sheela, 2008)
We found that local auxin response in the stem cutting base was required for adventitious rooting, and that this local auxin maximum was dynamically established by active polar auxin transport (PAT) from the leaves
Our results provide a detailed view of the major pathways triggering AR formation and how differential auxin homeostasis in the stem cutting base might account for cultivardependent adventitious rooting in carnation stem cuttings
Summary
New carnation (Dianthus caryophyllus) cultivars are mainly bred for traits affecting flower morphology, such as flower size, petal shape, petal number, flower color, and flower vase-life among others, as well as for traits improving plant production and pathogen resistance (Sheela, 2008). We found significant crosstalk between auxin levels, stress hormone homeostasis, and sugar availability in the stem cutting base of “Master” during the initial steps of adventitious rooting (Agulló-Antón et al, 2014). To further characterize these interactions, we made use of a large collection of commercial carnation cultivars selecting two additional cultivars because of their contrasting rooting performance (Birlanga et al, 2015). We characterized gene expression and functional changes in the stem cutting base during the early stages of adventitious rooting in these two cultivars, which provided a number of molecular, histological, and physiological markers to initiate the genetic dissection of AR formation in this species (Villacorta-Martín et al, 2015)
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