RING-type E3 ligase RhSAREL promotes flower senescence by differentially regulating two TMBIM family members, RhTMBIM1 and RhTMBIM7, in Rosa hybrida

Flower senescence significantly impacts the postharvest quality of cut roses (Rosa hybrida). E3 ligases orchestrate a diverse array of processes in plants, including organ development and stress responses. However, the molecular mechanisms of E3 ligases in flower senescence remain largely unknown. Here, we report that Senescence-associated RING-type E3 ligase (RhSAREL), a RING-H2 E3 ligase gene, is highly expressed at the early stage of flower senescence. RhSAREL-RNAi transgenic rose plants showed increased flower longevity. We confirmed that RhSAREL interacts individually with two Transmembrane BAX Inhibitor-1 Motif-containing (TMBIM) family proteins, RhTMBIM1 and RhTMBIM7, both in vivo and in vitro. Both RhTMBIM1 and RhTMBIM7 showed stable transcript levels during flower senescence, while silencing RhTMBIM1 or RhTMBIM7 accelerated flower senescence. Biochemical assays revealed that RhSAREL ubiquitinates RhTMBIM7 and promoted its degradation via the 26S proteasome pathway, but not so for RhTMBIM1. Protein docking and interface analysis showed that RhSAREL blocks RhTMBIM1’s calcium (Ca²⁺) leakage channel through its key N-terminal 26-amino-acid region. This interaction conformation disrupts RhTMBIM1-mediated Ca²⁺ homeostasis, thereby accelerating petal programmed cell death and senescence. Taken together, the RING-H2 E3 ligase RhSAREL promotes rose flower senescence by differentially regulating RhTMBIM1 and RhTMBIM7 via E3 ligase activity-independent and -dependent pathways, respectively.