The 14‐3‐3 Protein SlTFT1 Accelerates Tomato Fruit Ripening by Binding and Stabilising YFT1 in the Ethylene Signalling Pathway

Abstract

Ethylene plays a pivotal role during the fruit ripening process in tomato (Solanum lycopersicum). Previously, we have reported that the tomato EIN2‐like protein YELLOW‐FRUITED TOMATO1 (YFT1), a core component in the ethylene signal transduction pathway, exerts a critical regulatory function in the tomato fruit ripening process. However, the molecular mechanism of YFT1‐mediated ethylene signalling during tomato ripening still remains largely unknown. In this study, we performed yeast two‐hybrid screens of a cDNA expression library from tomato fruits and obtained a new YFT1‐interacting protein, SlTFT1 (TOMATO FOURTEEN‐THREE PROTEIN 1), and confirmed their interaction in vitro and in vivo. Further bimolecular fluorescence complementation (BiFC) assays indicated that SlTFT1 can specifically bind the canonical and non‐canonical on the carboxyl terminus of YFT1 (YFT1‐C). Triple response assays and ethylene responsive gene expression analysis demonstrated that SlTFT1 positively regulates the ethylene signalling pathway in a YFT1‐dependent manner. Phenotypical and biochemical analysis of SlTFT1 overexpression lines and loss‐of‐function mutants showed that SlTFT1 significantly accelerated ethylene emission, chromoplast development, lycopene accumulation and fruit ripening rates; however, the deletion of YFT1 and/or SlTFT1 lesion generated the opposite results, suggesting that SlTFT1 positively regulates tomato fruit ripening also in a YFT1‐dependent manner. Co‐expression and western blotting assays showed that SlTFT1 can efficiently prevent YFT1 from protein degradation mediated by an F‐box protein SlETP2‐like3, suggesting that SlTFT1 can stabilise YFT1 through their physical interaction. Collectively, our results reveal a genetic and molecular framework of the SlTFT1‐YFT1 complex, which modulates tomato fruit ripening by regulating ethylene signalling.