Background: Blueberry (Vaccinium spp.) is characterized by the production of berries that are smaller than most common fruits, and the underlying mechanisms of fruit size in blueberry remain elusive. V. corymbosum ‘O’Neal’ and ‘Bluerain’ are commercial southern highbush blueberry cultivars with large- and small-size fruits, respectively, which mature ‘O’Neal’ fruits are 1 ~ 2-fold heavier than those of ‘Bluerain’. In this study, the ontogenetical patterns of ‘O’Neal’ and ‘Bluerain’ hypanthia and fruits were compared, and comparative transcriptomic analysis was performed during early fruit development. Results: V. corymbosum ‘O’Neal’ and ‘Bluerain’ hypanthia and fruits exhibited intricate temporal and spatial cell proliferation and expansion patterns. Cell division before anthesis and cell expansion after fertilization were the major restricting factors, and outer mesocarp was the key tissue affecting fruit size variation among blueberry genotypes. Comparative transcriptomic and annotation analysis of differentially expressed genes revealed that the plant hormone signal transduction pathway was enriched, and that jasmonate-related TIFYs genes might be the key components orchestrating other phytohormones and influencing fruit size during early blueberry fruit development. Conclusions: These results provided detailed ontogenetic evidence for determining blueberry fruit size, and revealed the important roles of phytohormone signal transductions involving in early fruit development. The TIFY genes could be useful as markers for large-size fruit selection in the current breeding programs of blueberry.

Cross-pollination can improve the fruit set and quality of blueberry (Vaccinium spp.) for growers and consumers. However, the xenia effect in southern highbush blueberry remains unclear. Therefore, we selected eight cultivars of southern highbush blueberry (Vaccinium corymbosum L., interspecific hybrids) and applied pollination treatments (i.e., artificial self-pollination, artificial pollination with mixed pollen, or artificial pollination with individual cultivar pollen) to explore the xenia effects on the fruit set and quality of ‘O’Neal’ and ‘Emerald’. Pollen viability tests indicated that all of the cultivars are capable of fertilization. The highest fruit set came from ‘Bluerain’ pollen for ‘O’Neal’, while ‘Gulfcoast’ pollen increased fruit set the most in ‘Emerald’. Principal component analysis revealed that the cross combinations ‘Emerald’ × ‘Gulfcoast’ and ‘O’Neal’ × ‘Gulfcoast’ optimized the external and interior quality of the fruit. SSR was applied to determine which pollen source yielded the most seedlings. Results indicated that ‘Emerald’ × ‘Gulfcoast’ and ‘O’Neal’ × ‘Bluerain’ increased seedling production. Our results demonstrate that the xenia effects of ‘Gulfcoast’ pollen may increase ‘Emerald’ yields and promote fruit quality, while pollen from ‘Bluerain’ or ‘Jewel’ can improve ‘O’Neal’ fruit quality and seed number. Hence, these cross combinations may be utilized in blueberry production to increase fruit set, yield, and quality.

Blueberry (Vaccinium corymbosum) is reputed as a rich source of health-promoting phytonutrients, which contributes to its burgeoning consumer demand and production. However, blueberries are much smaller and have lower yields than most domesticated berries, and the inherent regulatory mechanisms remain elusive. In this study, the cytological and physiological changes, as well as comparative transcriptomic analysis throughout flower and fruit development in the southern highbush blueberry cultivar ‘O’Neal’ were performed. ‘O’Neal’ hypanthium and fruit exhibited a distinctive cell proliferation pattern, and auxin accumulation was unusual throughout development, while abscisic acid (ABA) levels rapidly increased in association with anthocyanin accumulation, total phenolic reduction and fruit maturation. Transcriptomic data showed that many differentially expressed genes (DEGs) were specifically expressed at each flower bud and fruit developmental stage. Further weighted gene co-expression network analysis (WGCNA) revealed numerous DEGs that correlated with the cell numbers of outer mesocarp and columella, showed two distinctive expression patterns. Most of the DEGs involved in auxin biosynthesis, transportation and signal transduction were upregulated, and this upregulation was accompanied by cell expansion, and flower bud and fruit development. However, individual members ofVcSAUR50andVcIAA9families might be insensitive to auxin, suggesting that these genes play a distinctive role in the growth and development of blueberry fruits. These results will support future research to better understand the flower and fruit development of southern highbush blueberry.

Endodormancy is the stage that perennial plants must go through to prepare for the next seasonal cycle, and it is also an adaptation that allows plants to survive harsh winters. Blueberries (Vaccinium spp.) are known to have high nutritional and commercial value. To better understand the molecular mechanisms of bud dormancy release, the transcriptomes of flower buds from the southern highbush blueberry variety “O’Neal” were analyzed at seven time points of the endo- and ecodormancy release processes. Pairwise comparisons were conducted between adjacent time points; five kinds of phytohormone were identified via these processes. A total of 12,350 differentially expressed genes (DEGs) were obtained from six comparisons. Gene Ontology analysis indicated that these DEGs were significantly involved in metabolic processes and catalytic activity. KEGG pathway analysis showed that these DEGs were predominantly mapped to metabolic pathways and the biosynthesis of secondary metabolites in endodormancy release, but these DEGs were significantly enriched in RNA transport, plant hormone signal transduction, and circadian rhythm pathways in the process of ecodormancy release. The contents of abscisic acid (ABA), salicylic acid (SA), and 1-aminocyclopropane-1-carboxylate (ACC) decreased in endo- and ecodormancy release, and the jasmonic acid (JA) level first decreased in endodormancy release and then increased in ecodormancy release. Weighted correlation network analysis (WGCNA) of transcriptomic data associated with hormone contents generated 25 modules, 9 of which were significantly related to the change in hormone content. The results of this study have important reference value for elucidating the molecular mechanism of flower bud dormancy release.

Chinese bayberry (Myrica rubra or Morella rubra) is a valuable fruit, yet the mechanism of its flesh segment development is not well understood. Using paraffin sectioning, we investigated the flower buds of the ‘Biqi’ and ‘Zaojia’ varieties, revealing that the flesh segment development in these Chinese bayberry varieties involved the formation of a primordium outside the ovary wall, the establishment of a simple columnar structure, and the formation of the primary flesh segment. Assessment of endogenous hormone levels indicated the significant reductions in jasmonic acid (JA) and indole-3-acetic acid (IAA) levels at the critical stages of flesh segment development. Correlation analysis highlighted the essential roles of IAA, JA, abscisic acid (ABA), and gibberellins in the flesh segment developmental process, underscoring the complex interactions driven primarily by the IAA, JA, and ABA networks. Gene modules positively correlated with flesh segment development were identified using transcriptome-based weighted gene co-expression network analysis (WGCNA). Differentially expressed genes (DEGs) were enriched in plant hormone signal transduction pathways, particularly for upregulated genes associated with auxin and JA signaling. Key genes predicted to be involved in flesh segment development included LAX2 and LAX3 (auxin transport), JAZ6 (JA signaling repression), and KAN1 and KAN4 (regulating multiple hormonal signaling pathways). Quantitative real-time polymerase chain reaction (qRT-PCR) validation confirmed that the expression trends for these genes were consistent across both varieties, particularly for CRC, SEP1, SEP3, IAA7, and JAZ6. Immunofluorescence localization studies revealed that auxin was primarily distributed in the central vascular bundle and outer cells of the flesh segment. This uneven auxin distribution might contribute to the unique morphology of flesh segments. Overall, this study provides insights into the hormonal regulation and genetic factors involved in the development of Chinese bayberry flesh segments.

Global warming leads to premature dormancy release and untimely flowering in southern highbush blueberry during winter, resulting in chilling injury and yield losses. However, effective strategies to delay flowering by modulating dormancy progression without compromising fruit quality remain lacking. This study demonstrated through field trials that spraying 1 mg/mL ethephon (ETH) during the early endodormancy stage effectively delayed dormancy release and reduced the bud break rate of spring shoots by approximately 33.92% relative to the control, with no adverse effects on fruit quality. The treatment also reduces sucrose content in floral buds, a change potentially associated with dormancy maintenance. To explore the molecular basis of this process, we examined two ethylene-responsive transcription factors, VcERF112 and VcERF115, previously identified in our laboratory. Their expression was rapidly upregulated following ETH treatment. Heterologous expression of either gene in Arabidopsis delayed both seed germination and flowering, suggesting a conserved growth-suppressive function. Dual-luciferase reporter assays confirmed that VcERF112 and VcERF115 bind to the T2 region (−2310 to −1595 bp) of the VcBRC1 (VcBRANCHED1) promoter and enhance its expression. In contrast, sucrose treatment suppressed VcBRC1 expression. Collectively, these results propose that ethylene may sustain bud dormancy through a coordinated mechanism that operates independently of the classic abscisic acid (ABA)/gibberellins (GA) balance, a relationship not addressed in this study. This mechanism involves the induction of VcERF112/115 to activate VcBRC1, coupled with the reduction in sucrose levels to alleviate its repressive effect on VcBRC1. These findings provide new molecular insights into the ethylene-mediated regulatory network underlying bud dormancy in blueberry.