F-box protein SlAMR1 negatively regulates tomato ascorbic acid biosynthesis throught ubiquitin pathway

Abstract

Ascorbic acid (AsA), as an antioxidant, plays vital roles in diverse physiological processes of plants. Engineering its biosynthesis in staple vegetables, such as tomato (Solanum lycopersicum L.), could offer new strategies for developing functional foods to promote human health. Although the regulatory role of AMR1 in AsA biosynthesis has been confirmed in Arabidopsis thaliana L., its regulatory mechanism in vegetable crops like tomato remains unclear. This study identified through homologous sequence alignment that SlAMR1 (ascorbic acid mannose pathway regulator 1), an F-box family protein in tomato, shares the highest amino acid sequence similarity (27 %) with Arabidopsis AMR1. In comparison with wild-type plants, SlAMR1 RNAi plants exhibited enhanced oxidative stress tolerance, and significantly elevated AsA accumulation in leaves and fruits, while over-expression lines showed opposite phenotypes. QPCR and enzyme activity analysis revealed that SlAMR1 suppresses AsA biosynthesis by regulating the mannose/galactose pathway. A 48-hours photoperiodic experiment indicated light-dependent transcriptional dynamics of SlAMR1. Further yeast two-hybrid assay and ubiquitination analysis confirmed that SlAMR1 modulates tomato AsA biosynthesis through the ubiquitin-proteasome complex pathway. The results elucidates the critical role of SlAMR1 in tomato AsA biosynthesis and provides a theoretical foundation for improving quality traits via molecular breeding approaches.