Anthocyanins, polyphenols conferring fruit coloration, are beneficial for human health. The tomato line “SunBlack” synthesizes anthocyanins in the fruit peel under light, producing purple fruits thanks to the myb-atv and Aft alleles. Light and temperature can crucially affect pigmentation in fruits. Whereas high light exposure or cool temperatures are required to allow strong purple colouration, shade or high temperatures repress anthocyanin synthesis.
To investigate this photo/thermo-dependent process, we focused on its major players: COP1, the negative regulator of photomorphogenesis which tags its targets for degradation under dark, and HY5, the master-positive regulator, which activates many processes under light, included anthocyanin biosynthesis.
We evaluated the activity of four BBX factors as HY5 cofactors under light. We analysed their expression levels, possible interactions with HY5 and other light signalling proteins and produced stable overexpression lines showing higher pigment contents.
We also evaluated COP1 and HY5 content under different conditions in the fruit, their gene expressions and molecular targets. We finally showed how COP1 levels in the nucleus increase with temperature, allowing HY5 degradation, and consequent inhibition of anthocyanin production, even under light.
Our study provides new insights into the complex network of light and temperature cross-talk regulating anthocyanin synthesis in tomato fruits.