Functional characterization of auxin-mediated dark stimulation of adventitious root formation in Petunia

• Applicant: Privatdozent Dr. Uwe Drüge
• Subject Area: Plant Cultivation, Plant Nutrition, Agricultural Technology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 516609515

Adventitious root formation in shoot tip cuttings is the most important basis for vegetative propagation of horticultural crops. This applies also to petunia, which ranks among the top bedding plants worldwide and has increasingly been developed as model plant for research on horticultural crops. Our previous work with Petunia hybrida ‘Mitchell’ has shown, that dark incubation of cuttings before planting strongly accelerates AR formation so that the time of subsequent cultivation in heated greenhouses can be significantly reduced. The dark-stimulated adventitious root formation in the stem base is associated with locally enhanced accumulation of the auxin indole-3-acetic acid and upregulation of genes that encode the auxin efflux transporter PIN1 and several components of the auxin signal transduction chain. The enhanced auxin accumulation in the stem base depends on the upper shoot section, while the auxin signalling is also subject to the nitrogen content of the cutting. The proposed project aims to elucidate the critical molecular factors and processes at the level of whole cuttings that determine the dark-enhanced auxin delivery towards the stem base and the stimulation of auxin signalling. Potential effects of darkness on the auxin source in the upper cutting section, on competing auxin sinks, on auxin transport efficiency and the auxin interrelationships with metabolites and other hormones will be investigated. To this end, two genome-sequenced parental petunia species that contrast in the rooting response to darkness will be compared. A specially designed microarray, that covers all known auxin-, jasmonic acid- and strigolactone-related genes in petunia and quantitative RT-PCR will be combined with hormone analysis, auxin transport studies and inter- and intracellular PIN localization to identify the molecular and biochemical processes underlying the dark-mediated plant hormone homeostasis and signalling at the level of distinct cutting organs. Pharmacological tools will be used to manipulate plant hormone and metabolite homeostasis or signalling. The function of selected candidate genes for dark-promoted adventitious root formation and their tissue specific expression are investigated with the help of Agrobacterium-mediated transformation and mutagenesis using RNA-guided Cas endonucleases. The project is intended to expand the understanding of the dark-/light-mediated endogenous control of auxin homeostasis and signalling at whole cutting level and open up new perspectives on how this can be aligned to the target value “root regeneration” so that inputs of heating energy and of synthetic auxins can be reduced in vegetative propagation.

• DFG Programme: Research Grants