Toward Systematic Understanding of Flower Bud Induction in Apple: A Multi-Omics Approach

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.

Time-Resolved Analysis of Candidate Gene Expression and Ambient Temperature During Bud Dormancy in Apple

“…Chill portions (CP) were calculated by the dynamic model by Fishman et al (1987a , b) ; Erez et al (1990) . Heat accumulation was calculated using the ASYMCUR GDH model by Anderson with the base, optimal, and critical temperatures of 4°C, 25°C, and 36°C, respectively ( Anderson et al, 1986 ; Milyaev et al, 2021 ).…”

Metabolic Pathways for Observed Impacts of Crop Load on Floral Induction in Apple

“…Histological analysis has shown that the initial development of a flower bud coincides with a developing embryo or fruitlet [ 6 ]. The developing seed in young fruitlets is believed to repress flower induction in vegetative buds via phytohormones and removal of fruitlets at the 3–18 mm fruit size, through thinning practices have been shown to lead to a more consistent flower formation (return bloom) for the following season [ 3 , 7 , 8 ].…”

“…Flowering in apple involves four stages: floral induction (FI), flower bud initiation, differentiation, and floral bloom [ 3 , 6 , 11 ]. FI occurs when a chemical and/or environmental signal causes a vegetative bud to become floral.…”

Transcriptomic Insight into Underground Floral Differentiation in Erythronium japonicum

“…Advances in omics have increased our understanding of complex mechanisms regulating plant growth and development [24][25][26][27][28][29]. Multiple approaches including, transcriptomics [30][31][32], genomics [33,34], phenomics [35,36], and proteomics [37,38] have been used for uncovering flowering mechanism in plants.…”