Flavonoids represent the main class of plant secondary metabolites and occur in the tissues and organs of various plant species. In plants, flavonoids are involved in many biological processes and in response to various environmental stresses. The consumption of flavonoids has been known to reduce the risk of many chronic diseases due to their antioxidant and free radical scavenging properties. In the present review, we summarize the classification, distribution, biosynthesis pathways, and regulatory mechanisms of flavonoids. Moreover, we investigated their biological activities and discuss their applications in food processing and cosmetics, as well as their pharmaceutical and medical uses. Current trends in flavonoid research are also briefly described, including the mining of new functional genes and metabolites through omics research and the engineering of flavonoids using nanotechnology. This review provides a reference for basic and applied research on flavonoid compounds.

The spectral composition of light influences the biosynthesis of flavonoids in many plants. However, the detailed composition of flavonoids and anthocyanins and the molecular basis for their biosynthesis in strawberry fruits under two light-quality treatments, red light supplemented with blue light (RB) and ultraviolet B (UVB) irradiation, remain unclear. In this study, the content of flavonoids and anthocyanins was significantly increased in strawberry fruits under RB light and UVB, respectively. The content of flavonoids and anthocyanins in strawberry fruits under UVB light was dramatically higher than that in strawberry fruits irradiated with RB light, and a total of 518 metabolites were detected by means of LC-MS/MS analysis. Among them, 18 phenolic acids, 23 flavonoids, and 8 anthocyanins were differentially accumulated in the strawberry fruits irradiated with red/blue (RB) light compared to 30 phenolic acids, 46 flavonoids, and 9 anthocyanins in fruits irradiated with UVB. The major genes associated with the biosynthesis of flavonoids and anthocyanins, including structural genes and transcription factors (TFs), were differentially expressed in the strawberry fruits under RB and UVB irradiation, as determined through RNA-seq data analysis. A correlation test of transcriptome and metabolite profiling showed that the expression patterns of most genes in the biosynthesis pathway of flavonoids and anthocyanins were closely correlated with the differential accumulation of flavonoids and anthocyanins. Two TFs, bZIP (FvH4_2g36400) and AP2 (FvH4_1g21210), induced by RB and UVB irradiation, respectively, exhibited similar expression patterns to most structural genes, which were closely correlated with six and eight flavonoids, respectively. These results indicated that these two TFs regulated the biosynthesis of flavonoids and anthocyanins in strawberry fruit under RB light and UVB, respectively. These results provide a systematic and comprehensive understanding of the accumulation of flavonoids and anthocyanins and the molecular basis for their biosynthesis in strawberry fruits under RB light and UVB.

Gibberellins (GAs) are pivotal phytohormones regulating fruit development, yet the molecular mechanisms by which they modulate strawberry fruit size and quality remain elusive. Here, we investigated the effects of exogenous GA₃ on the fruit development of the cultivated strawberry (Fragaria × ananassa ‘Benihoppe’). Treatment with 20 mg/L GA₃ significantly promoted fruit enlargement, advanced ripening by 7 days, and increased fruit weight and dimensions. Integrated transcriptomic and targeted metabolomic analyses revealed that GA₃ application induced a substantial reprogramming of the endogenous hormone landscape, notably triggering a significant increase in auxin (IAA) levels. Transcriptome profiling identified numerous differentially expressed genes (DEGs), with KEGG enrichment analysis highlighting the “plant hormone signal transduction” pathway as the most significantly enriched. Further analysis pinpointed key DEGs involved in auxin signaling (AUX/IAA, ARF, GH3, and SAUR) and gibberellin perception (GID1), suggesting a central role for auxin-mediated processes in GA₃-induced fruit expansion. We propose that exogenous GA₃ promotes strawberry fruit development through a synergistic mechanism: (1) enhancing the biosynthesis of endogenous bioactive GAs; (2) activating auxin signal transduction pathways to drive cell expansion; and (3) attenuating the repression of DELLA proteins. Our study unveils the critical role of the GA₃-IAA signaling axis in strawberry fruit development, providing a theoretical foundation for harnessing hormone regulation to improve fruit yield and quality in strawberry production.