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.

Transcriptomic and Physiological Analysis Reveals the Responses to Auxin and Abscisic Acid Accumulation During Vaccinium corymbosum Flower Bud and Fruit Development

“…According to previous study ( Yang et al, 2021 ), the cell number and area of outer mesocarp and columella at the stages of III∼IV, S0∼S2 and S4∼S5 were significant different during floral and fruit development between large-size cultivar ‘O’Neal’ and small-size cultivar ‘Bluerain,’ indicating these 8 specific stages we chose were more important for southern highbush blueberry fruit growth and development. To understand the regulatory mechanisms of ‘O’Neal’ flower bud and fruit development, especially for fruit size/weight, transcriptomic data were generated by high-throughput RNA-seq.…”

“…Since the floral and young fruit phases (before and after anthesis) were the important stages for blueberry cell proliferation and cell expansion initiation, respectively ( Yang et al, 2021 ), the transcriptomic data of samples at stage ONS0 (growth arrest period) as comparison standards, and DEGs at different developmental stages were analyzed ( Table 1 ). With the exception of 14,609 DEGs from the ONIV vs .…”

“…This may explain why approximately 2/3 of new ‘O’Neal’ fruit cells were produced before anthesis, but the total cell number remained constant throughout fruit development until maturation. In addition, our prior studies measuring equatorial and vertical cell layers ( Yang et al, 2019 , 2021 ) indicated that anticlinal and periclinal divisions simultaneously occurred during blueberry flower bud enlargement and the second rapid fruit growth phase, but were restrained at the arrest phase.…”

“…However, the cell proliferation pattern of ‘O’Neal’ fruit was differentiated from the model fruit growth pattern. ‘O’Neal’ outer mesocarp exhibited the highest mitotic activity throughout development, whereas the cell number of columella decreased dramatically ( Yang et al, 2021 ). This may explain why approximately 2/3 of new ‘O’Neal’ fruit cells were produced before anthesis, but the total cell number remained constant throughout fruit development until maturation.…”

“…Because only a weak peak of respiration and ethylene production has been reported during blueberry maturation ( Windus et al, 1976 ; Suzuki et al, 1997 ), ABA is believed to be the key phytohormone of ripening processes and pigment accumulation, and to respond to internal and external environmental changes ( Kumar et al, 2014 ; Liao et al, 2018 ; Han et al, 2021 ; Kou et al, 2021 ). During fruit ripening, the firmness of ‘O’Neal’ fruits decreased rapidly beginning at stage S5 (unpublished data), and the cell walls of middle mesocarp collapsed ( Yang et al, 2021 ). Meanwhile, ABA and anthocyanin began to accumulate rapidly ( Figure 2 ).…”