A BBX-HY5 photomorphogenic module induces anthocyanin synthesis in purple tomato fruits

Over the last decades, the search for novel nutraceutical foods led to the development of several anthocyanin enriched crops, with the purple tomato being one of the most prominent examples. In non-GM purple tomato, anthocyanin biosynthesis in fruits is conferred by the introgression of specific alleles of Anthocyanin fruit (Aft) and atroviolacea (atv) genes, which allow the pigmentation of the epicarp under optimal environmental conditions. Light induces anthocyanin synthesis through ELONGATED HYPOCOTYL 5 (HY5), whose levels are in turn controlled by CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1)-targeted destabilization. In recent years, light-related HY5-independent factors have been object of research. In this work, we have identified two novel transcription factors, belonging to the BBX protein family, modulating anthocyanin synthesis in purple tomato fruits at different stages of the pathway, including transcriptional and post-translational levels, and showing both HY5-dependent and independent functions. Our results contribute to expanding the knowledge on the light-induced regulation of anthocyanin synthesis in tomato and may serve for the development of novel anthocyanin enriched lines able to overcome the threat posed by non-optimal light conditions.