Comparative anatomical and transcriptomic insights into Vaccinium corymbosum flower bud and fruit throughout development

Abstract

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.

Keywords: Blueberry; Cell expansion; Cell proliferation; Comparative transcriptome; Fruit development; TIFY genes.

Fig. 1

Developmental stages of V. corymbosum ‘O’Neal’ and ‘Bluerain’ flower buds and fruits. a Developmental stages of ‘O’Neal’ and ‘Bluerain’ flower buds and fruits. b Microscopic structures of ‘O’Neal’ fruit (stage S0) analyzed by equatorial paraffin section. c, d, e Quantification of fruit weight, horizontal and vertical diameters at different developmental stages. Co: columella; Ep: epidermis; Hp: hypodermis; Om: outer mesocarp; Mm: middle mesocarp; Im: inner mesocarp; En: endocarp

Fig. 2

Spatiotemporal change of cell number and cell area throughout V. corymbosum ‘O’Neal’ and ‘Bluerain’ hypanthia/fruit development. Co: columella; Ep: epidermis; Hp: hypodermis; Om: outer mesocarp; Mm: middle mesocarp; Im: inner mesocarp; En: endocarp

Fig. 3

Comparative transcriptomic analysis of V. corymbosum ‘O’Neal’ and ‘Bluerain’ hypanthia/fruit during early fruit development. a Numbers of detected expressed genes for each sample. b Principal component analysis (PCA) of 18 transcriptomic profiles. c Cluster analysis of DEG expression patterns. d Up- and down-regulated DEGs identified in the 5 comparisons. e Venn diagrams of DEGs

Fig. 4

Expression profile of TIFYs of V. corymbosum ‘O’Neal’ and ‘Bluerain’ hypanthia/fruit during early fruit development. Each stage of early fruit development in ‘O’Neal’ and ‘Bluerain’ was listed horizontally. The color represented the expression level (Log₂FPKM) of DEGs, and the FPKM value was the fragments per kilobase of transcript per million fragments

Fig. 5

Spatiotemporal growth and developmental models of V. corymbosum hypanthia/fruit. Co: columella; Ep: epidermis; Hp: hypodermis; Om: outer mesocarp; Mm: middle mesocarp; Im: inner mesocarp; En: endocarp

Fig. 6

JA might be a master regulator for V. corymbosum fruit size/weight during early development