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Brassinosteroids signaling component SlBZR1 promotes fruit ripening in tomato

Fruit ripening evolved to be attractive to frugivores that derive energy and nutrition from the fruits in exchange for assisting seed dispersal, which is accompanied by the dramatically change of fruit characteristics, including color, aroma, and texture. The plant hormone ethylene plays a key role in climacteric fruit ripening, while the role of other phytohormones as well as their cross talk with ethylene in modulating fruit ripening remains elusive. Here, we report growth-promoting phytohormone brassinosteroids promote fruit ripening in tomato through regulation of ethylene biosynthesis. Exogenous BR treatment and the increase of endogenous BR content in SlCYP9OB3-OE promoted ethylene production and fruit ripening. SlBZR1, a central component and positive regulator of BR signaling pathway, promotes ethylene production and carotenoid accumulation through direct transcriptional regulation of SlACO1, SlACO3 and SlPSY1. Furthermore, SlBIN2, a negative regulator of BR signaling upstream of SlBZR1, decreases ethylene production and carotenoid accumulation. Together, our results demonstrate that BR signaling integrates ethylene and carotenoid biosynthetic pathway to regulate fruit ripening.