Abstract
Flowering and fruit set are important traits affecting fruit quality and yield in rabbiteye blueberry (Vaccinium ashei). Intense efforts have been made to elucidate the influence of vernalization and phytohormones on flowering, but the molecular mechanisms of flowering and fruit set remain unclear. To unravel these mechanisms, we performed transcriptome analysis to explore blueberry transcripts from flowering to early fruit stage. We divided flowering and fruit set into flower bud (S2), initial flower (S3), bloom flower (S4), pad fruit (S5), and cup fruit (S6) based on phenotype and identified 1,344, 69, 658, and 189 unique differentially expressed genes (DEGs) in comparisons of S3/S2, S4/S3, S5/S4, and S6/S5, respectively. There were obviously more DEGs in S3/S2 and S5/S4 than in S4/S3, and S6/S5, suggesting that S3/S2 and S5/S4 represent major transitions from buds to fruit in blueberry. GO and KEGG enrichment analysis indicated these DEGs were mostly enriched in phytohormone biosynthesis and signaling, transporter proteins, photosynthesis, anthocyanins biosynthesis, disease resistance protein and transcription factor categories, in addition, transcript levels of phytohormones and transporters changed greatly throughout the flowering and fruit set process. Gibberellic acid and jasmonic acid mainly acted on the early stage of flowering development like expression of the florigen gene FT, while the expression of auxin response factor genes increased almost throughout the process from bud to fruit development. Transporter proteins were mainly associated with minerals during the early flowering development stage and sugars during the early fruit stage. At the early fruit stage, anthocyanins started to accumulate, and the fruit was susceptible to diseases such as fungal infection. Expression of the transcription factor MYB86 was up-regulated during initial fruit development, which may promote anthocyanin accumulation. These results will aid future studies exploring the molecular mechanism underlying flowering and fruit set of rabbiteye blueberry.
Highlights
Flowering and fruit set are two of the most important events in the plant life cycle
Transgenic blueberry with overexpression of Vaccinium corymbosum FLOWERING LOCUS T (VcFT) has no chilling requirement for normal flowering [12], transgenic plants are smaller than untransformed plants
We explored the expression levels of genes involved in blueberry flower and fruit set at six stages (Fig 1A) using Cuffdiff software instead of edgeR
Summary
Flowering and fruit set are two of the most important events in the plant life cycle. In Arabidopsis, the key genes integrating multiple flowering pathways are FLOWERING LOCUS T (FT), SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1), and LEAFY (LFY). FT which is a florigen gene and SOC1 share the common upstream regulators CONSTANS (CO), a key component of the photoperiodic pathway, and FLOWERING LOCUS C (FLC), a flowering repressor integrating autonomous and vernalization pathways. Transgenic blueberry with overexpression of Vaccinium corymbosum FLOWERING LOCUS T (VcFT) has no chilling requirement for normal flowering [12], transgenic plants are smaller than untransformed plants. This suggests that VcFT is a primary integrator, but hinders the growth development of blueberry. Overexpression of DWARF AND DELAYED FLOWERING 1 (VcDDF1), which is associated with delayed flowering in Arabidopsis, can increase freezing tolerance with no effect on plant flowering time in blueberry [14]
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