Abstract
The induction of flower buds in apple (Malus × domestica Borkh.) is tightly connected to biennial bearing, which is characterized by alternating years with high (ON) and low or no (OFF) crop loads. In order to study this irregular cropping behavior, spur buds from ON- and OFF-trees of the biennial-bearing cultivar ‘Fuji’ and the regular bearing cultivar ‘Gala’ were collected. First, the time of flower bud initiation was precisely determined for both cultivars by histological analysis. Moreover, for a systematic understanding of flower bud induction in apple, the physiological and molecular mechanisms within the bud tissue were evaluated over four weeks prior to flower bud initiation by employing a multi-omics approach, including RNA sequencing, proteomic and metabolic profiling. Gene and protein enrichment analysis detected physiological pathways promoting and inhibiting early flower bud development. Metabolic profiles from the cropping treatments revealed a greater abundance of thiamine, chlorogenic acid, and an adenine derivative in spur buds from OFF-trees, whereas tryptophan was more abundant in the buds collected from ON-trees. Cultivar comparison indicated that chlorogenic acid was more abundant in ‘Gala’ than in ‘Fuji’ spur buds, whereas the opposite effect was found for tryptophan. Genes controlling tryptophan biosynthesis were not affected by ON- and OFF-treatments, but genes assigned to the metabolism of tryptophan into indoleacetate were differentially expressed between cultivars and treatments. The multi-omics approach permitted analyzing complex plant metabolic processes involved in early flower bud development and more specifically presumably in flower bud induction by tracing some pathways from gene to product level.
Highlights
Flower induction, initiation, and differentiation are developmental stages that vegetative buds need to undergo on their way to become floral
We acknowledge that there is a smooth transition from induction to initiation of flower buds, the signals in the gene to product pathway we found as early as four weeks prior to flower initiation can be assertively ascribed to flower induction
Observing flower bud meristem development by histological sectioning of apple buds sampled in the same experiment throughout the growing season of 2015, we identified flower initiation time points for ‘Fuji’ (75 days after full bloom, DAFB)
Summary
Initiation, and differentiation are developmental stages that vegetative buds need to undergo on their way to become floral. The target and the novelty of the current work is the application of NGS in combination with two non-targeted omics approaches to develop a systematic understanding of the complex plant metabolic processes involved in flower bud induction in apple and tracing some pathways from gene to product level. In the same experimental setup, we sampled apple buds for histological sectioning and revealed flower initiation time points for ‘Fuji’ and ‘Gala’ under field conditions in southwest Germany (Kofler et al, 2019) Considering these time points, we aimed to detect mobile signals potentially promoting or inhibiting flower bud induction such as peptides, phytohormones, phytohormonelike acting compounds, sugars, and secondary metabolites during 1–4 weeks prior to flower initiation and to link all the compounds of interest to genes and proteins involved in their biosynthesis and regulation. We summarize the results of RNA sequencing and non-targeted proteomic and metabolic profiling
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
