Cytokinin negatively regulates tomato fruit ripening by influencing the ethylene pathway

Reducing endogenous CK levels accelerates fruit ripening in tomato by regulating ethylene biosynthesis and signalling pathway. Tomato is a typical climacteric fruit and is recognized as one of the most important horticultural crops globally. The ripening of tomato fruits is a complex process, highly regulated by phytohormones. Cytokinin (CK) is a hormone that primarily impacts the early development of fruit, however its influence on fruit ripening has not been thoroughly investigated. In this study, we used both wild-type Micro-Tom and transgenic tomato plants that overexpress AtCKX2, a CK degradation gene driven by the fruit-specific promoter Tfm7, to investigate the effect of CK on tomato fruit ripening. Our findings revealed that reducing endogenous CK levels in transgenic plants can accelerate the ripening process of tomato fruits. Premature activation of ethylene biosynthetic genes and ripening regulator genes was upregulated in CK-deficient fruits. Moreover, the application of exogenous ethylene inhibitors resulted in delayed fruit ripening in CK-deficient fruits. These results together suggest that CK plays a negative role in tomato fruit ripening by affecting the ethylene pathway.