SlAN1 is a limiting factor for the light-dependent anthocyanin accumulation in fruit tissues of purple tomato

Anthocyanins are specialized plant metabolites with significant dietary value due to their anti-inflammatory properties. Research indicates that dietary intake of these phenolic compounds contributes to preventing various chronic diseases. As the most consumed vegetable worldwide, tomato ( Solanum lycopersicum ) is an excellent candidate for anthocyanin-enrichment strategies. In tomato, activation of anthocyanin biosynthesis is light-dependent, but this mechanism has yet to be entirely characterized. We investigated the role of light in anthocyanin biosynthesis in fruits of the purple tomato, which is a near-isogenic line (NIL) derived from wild accessions into cv. Micro-Tom (MT). MT- Aft/atv/hp2 starts accumulating anthocyanin early during fruit development but is restricted to the peel (exocarp and epicarp). Manipulating light incidence in different fruit tissues determined that the absence of anthocyanin accumulation in the flesh results from the sun-blocking effect of the cyanic epicarp on the mesocarp, thus preventing light from penetrating deeper into the fruit. Transcriptional analyses of the fruit peel and flesh revealed that the bHLH transcription factor SlAN1 (Solyc09g065100) is the limiting factor for light-dependent anthocyanin accumulation in both tissues. This research enhances our comprehension of the genetic and environmental regulation of anthocyanin accumulation in fruit tissues, offering valuable insights into plant breeding for human nutrition. Highlight The expression of the SlAN1 gene is activated in response to light signals, and it is the limiting factor for anthocyanin pigmentation in tomato fruit tissues. ### Competing Interest Statement The authors have declared no competing interest.