Mechanisms of exogenous GA3-induced inhibition of seed development in southern highbush blueberry (Vaccinium darrowii)

Abstract

Blueberry fruit, is flavorful and nutrient, rich and has very broad market prospects. Seedless blueberries are preferred by consumers when eaten fresh, preserved or processed. Here, 50, 100, and 150 mg/L gibberellic acid (GA3) were used to treat the flowers of ' Sharpblue ' blueberry after 5 and 10 days of full opening, resulting in varying seed abortion rates. The 50 mg/L GA3 treatment yielded the lowest seedlessness rate, fruit shape index, and fruit weight. Treatment with 150 mg/L GA3 inhibited fruit expansion and prolonged ripening after treatment, although the seedlessness rate was 98.78%. In contrast, 100 mg/L GA3 induced 100% seedlessness and did not significantly affect the fruit phenotype, solid-to-acid ratio, or firmness compared to those of control seeded fruit. The brassinosteroid (BR), cytokinin (CTK), zeatin (ZT), and ethylene (ETH) levels increased when the seeds stopped developing at the S2 stage under 100 mg/L GA3, while the abscisic acid (ABA) and indole-3-acetic acid (IAA) levels were lower than those in the control group. Transcriptome analysis revealed 87 differentially expressed genes (DEGs) related to phytohormones and 49 DEGs related to seed development. The expression of 21 genes potentially regulating seed development was initially validated by RT-qPCR, and the RT-qPCR results for 16 DEGs were consistent with their RNA-seq results. Additionally, comprehensive transcriptome and metabolome analyses revealed that the differentially expressed metabolite (DEM) (±)-abscisic acid had the strongest positive correlation with the DEG AMAT and the DEM gibberellic acid with DEG JAZ1. Collectively, the developmental process of blueberry fruit and seeds may be regulated by the synergistic effects of multiple hormones, and differential expression of 16 genes associated with seed development may influence seed abortion in blueberry fruit. This study investigated the effects of different concentrations of GA3 treatments on blueberry fruit seedlessness, fruit quality, and hormone and gene expression, providing valuable reference data for exploring the internal inhibition mechanism of blueberry seed development and inducing seedless blueberry fruit formation.