The mode of action of remorin1 in regulating fruit ripening at transcriptional and post-transcriptional levels

Remorins are plant-specific and plasma membrane-associated proteins that display a variety of functions in plant growth, development, biotic and abiotic stresses, and signal transduction. However, little information is available for understanding their role in fruit ripening. Here, remorin 1 (SlREM1) is cloned from tomato and its localization is examined by co-localization analysis and immunoblotting. Functions of SlREM1 in fruit ripening are characterized based on gene expression, co-immunoprecipitation coupled with mass spectroscopy and split luciferase complementation imaging assays in SlREM1 overexpression and RNA interference (RNAi) lines. The results indicate that SlREM1 is localized at the plasma membrane. Overexpression of SlREM1 in tomato stimulates fruit ripening with an increase in ethylene production and lycopene accumulation as compared to the wild-type. Consistently, these genes involved in ethylene and lycopene biosynthesis and ripening regulators also are upregulated in SlREM1 overexpression lines. SlREM1 can interact with ethylene biosynthesis proteins SAM1, ACO1 and ACS2 and is degraded by ubiquitin-mediated proteolysis. Our findings reveal that SlREM1 serves as a positive regulator of fruit ripening and provide novel cues for understanding of the molecular regulation network of fruit ripening.