The Identification of Regulatory Genes Involved in Light-Induced Anthocyanin Accumulation in Aft Tomato Developing Fruits

Anthocyanins, which accumulate in fruits, flowers, and vegetative organs, play a critical role in plant reproduction, disease resistance, stress tolerance, and promoting human health. Although light significantly influences the development of various fruit pigments, the specific mechanisms through which it regulates anthocyanin accumulation during fruit ripening are not yet fully understood. This study aimed to investigate the role of light in anthocyanin biosynthesis using Aft tomato fruits, which accumulate pigments in the epidermis. To explore the effects of light on anthocyanin biosynthesis, half of each fruit was covered with aluminum foil to establish light-exposed and bagged conditions for comparative analysis. The results showed that the bagged treatment led to a significant decrease in the total anthocyanin content of the fruits. Transcriptome analysis revealed a notable upregulation of several structural genes involved in the anthocyanin biosynthetic pathway, specifically Sl4CL, SlCHS, SlCHI, SlF3H, SlDFR, and Sl3GT in the light-exposed fruits. Additionally, the expression levels of light-responsive genes and transcription factors, such as SlCRY1, SlSPA, SlUVR3, SlHY5, SlBBX24, SlMYB11, MADS-box transcription factor 23, SlHD-ZIP I/II, SlAN2-like, SlbHLH and SlWD40 proteins, were significantly higher in the light-exposed samples compared to those subjected to the bagged treatment. Weighted Gene Co-Expression Network Analysis (WGCNA) demonstrated a strong association between light-induced gene expression such as SlPAL, SlCHS1, SlDFR, SlF3H, SlF3′5′H, SlANS, SlHY5, and SlAN2-like quantified by qRT-PCR analysis and anthocyanin biosynthesis. Moreover, as the fruit matured, both anthocyanin accumulation and the expression of genes related to its biosynthetic pathway increased. These findings contribute to a foundational understanding of the regulatory network that influences light-induced processes and fruit development impacting anthocyanin accumulation, which will facilitate in-depth study of the functions of these identified genes and provide a foundation for breeding anthocyanin-rich tomato varieties.