The interplay between light and transcriptional profile involved in anthocyanin biosynthesis in tomato fruit tissues

Abstract

Anthocyanins are specialized plant metabolites known for their vibrant pigmentation and potent antioxidant properties, offering significant benefits for both plant physiology and human health. These water-soluble phenolic compounds enhance stress tolerance in plants and play a protective role against chronic diseases when included in the human diet. The anthocyanin biosynthetic pathway is highly conserved across plant species and is regulated by a complex network of structural and transcriptional genes, with light serving as a critical environmental signal. In tomato (Solanum lycopersicum), a widely consumed horticultural crop and a promising candidate for anthocyanin biofortification, the photoregulation of anthocyanin biosynthesis remains incompletely understood. In this study, using anthocyanin-enriched tomato lines (MT-Aft/atv/hp2), it was revealed that anthocyanin accumulation is restricted to the peel (epicarp) due to limited light penetration into the fruit pulp. This finding implies that tissue-specific light exposure and transcriptional control, particularly the bHLH transcription factor SlAN1, are key determinants. Furthermore, the research highlights the central role of the COP1 (CONSTITUTIVE PHOTOMORPHOGENIC 1) protein, a ubiquitin E3 ligase, in repressing anthocyanin biosynthesis under dark conditions by targeting positive regulators for degradation. COP1 interacts with multiple transcription factors in an evolutionarily conserved manner across fruits of various species, including Arabidopsis, apple, pear, eggplant, and tomato. This study deepens our understanding of the genetic and post-translational regulation of anthocyanin biosynthesis, offering valuable insights for crop improvement, nutritional enhancement, and the development of natural colorants.