Strawberry COP9 signalosome FvCSN5 regulates plant development and fruit ripening by facilitating polyamine oxidase FvPAO5 degradation to control polyamine and H2O2 homeostasis

Polyamines (PAs), mainly including putrescine, spermidine, and spermine, are essential for plant growth and development. However, the post-translational regulation of PA metabolism remains unknown. Here, we report the COP9 signalosome subunit 5A (FvCSN5A)-mediated degradation of the PA oxidase FvPAO5, which catalyzes the conversion of spermidine/spermine to produce H2O2. FvCSN5A is localized in the cytoplasm and nucleus, ubiquitously expressed in strawberry plants, and rapidly increases during fruit ripening. FvCSN5A RNA interference (RNAi) transgenic strawberries exhibit pleiotropic effects on plant development, fertility, and fruit ripening by regulating PA and H2O2 homeostasis, similar to FvPAO5 overexpression transgenic lines. FvCSN5A interacts with FvPAO5 in vitro and in vivo. The ubiquitination and degradation of FvPAO5 are impaired in FvCSN5A RNAi lines. Additionally, FvCSN5A interacts with cullin 1 (FvCUL1), a core component of the E3 ubiquitin-protein ligase complex. Transient genetic analysis in cultivated strawberry fruits showed that inhibiting FaPAO5 expression could partially rescue the ripening phenotype of FaCSN5A RNAi fruits. Collectively, the CSN5A-CUL1-PAO5 signaling pathway responsible for PA and H2O2 homeostasis is crucial to strawberry vegetative and reproductive growth and, final to fruit ripening. Our findings may open a promising avenue for improving crop yield and quality by manipulating the CSN5-PAO5 pair.