Abstract
Adventitious root (AR) formation, which is controlled by endogenous and environmental factors, is indispensable for vegetative asexual propagation. However, comprehensive proteomic data on AR formation are still lacking. The aim of this work was to study indole-3-butyric acid (IBA)-induced AR formation in the dwarf apple rootstock ‘T337’. In this study, the effect of IBA on AR formation was analysed. Subsequent to treatment with IBA, both the rooting rate and root length of ‘T337’ increased significantly. An assessment of hormone levels in basal stem cuttings suggested that auxin, abscisic acid, and brassinolide were higher in basal stem cuttings that received the exogenous IBA application; while zeatin riboside, gibberellins, and jasmonic acid were lower than non-treated basal stem cuttings. To explore the underlying molecular mechanism, an isobaric tags for relative and absolute quantification (iTRAQ)-based proteomic technique was employed to identify the expression profiles of proteins at a key period of adventitious root induction (three days after IBA treatment). In total, 3355 differentially expressed proteins (DEPs) were identified. Many DEPs were closely related to carbohydrate metabolism and energy production, protein homeostasis, reactive oxygen and nitric oxide signaling, and cell wall remodeling biological processes; as well as the phytohormone signaling, which was the most critical process in response to IBA treatment. Further, RT-qPCR analysis was used to evaluate the expression level of nine genes that are involved in phytohormone signaling and their transcriptional levels were mostly in accordance with the protein patterns. Finally, a putative work model was proposed. Our study establishes a foundation for further research and sheds light on IBA-mediated AR formation in apple as well as other fruit rootstock cuttings.
Highlights
Apple (Malus x domestica Borkh.) is one of the most planted and utilized tree fruits in the world
According to previous anatomical studies in apple [4,27], basal stem samples treated with 1 mg·L−1 indole-3-butyric acid (IBA) and non-treated control were harvested at five key time points 0, 3, 7, 11, and 16 days after the treatment with IBA
Adventitious root (AR) formation was divided into four stages based on morphological changes: stage 1 represents cuttings just treated with IBA (0 day, Competent cells), stage 2 represents cuttings in the AR induction phase (3 day, Cell cycle reactivation), stage 3 represents cuttings in the AR initiation phase (7 day and 11 day, Activation of the callus formation and AR primordium), and stage 4 represents cuttings where ARs have broken through the epidermis and emerged (16 day, AR outgrowth) [28,29]
Summary
Apple (Malus x domestica Borkh.) is one of the most planted and utilized tree fruits in the world. There has been significantly increased demand for the breeding of dwarfing apple rootstocks. Asexual reproduction is widely used for rootstock breeding due to its high efficiency, short cycle, and maintenance of genetic stability. The induction of adventitious roots (ARs) from basal stem cuttings is a key step in the asexual reproduction of apple rootstocks. High-quality apple rootstocks play an important role in regulating the environmental adaptability of apple trees. ‘T337’, is a cultivar of apple dwarfing rootstock that is characterized by strong growth control, induction of early fruiting, high yields, and the production of high-quality apples from grafted scion cultivars. The study of the molecular regulatory mechanisms underlying AR formation in ‘T337’ apple rootstock has important theoretical and practical value for apple rootstock breeding
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