Abstract
Carotenoids are natural pigments that are indispensable to plants and humans, whereas the regulation of carotenoid biosynthesis by post-translational modification remains elusive. Here, we show that a tomato E3 ubiquitin ligase, Plastid Protein Sensing RING E3 ligase 1 (PPSR1), is responsible for the regulation of carotenoid biosynthesis. PPSR1 exhibits self-ubiquitination activity and loss of PPSR1 function leads to an increase in carotenoids in tomato fruit. PPSR1 affects the abundance of 288 proteins, including phytoene synthase 1 (PSY1), the key rate-limiting enzyme in the carotenoid biosynthetic pathway. PSY1 contains two ubiquitinated lysine residues (Lys380 and Lys406) as revealed by the global analysis and characterization of protein ubiquitination. We provide evidence that PPSR1 interacts with PSY1 precursor protein and mediates its degradation via ubiquitination, thereby affecting the steady-state level of PSY1 protein. Our findings not only uncover a regulatory mechanism for controlling carotenoid biosynthesis, but also provide a strategy for developing carotenoid-enriched horticultural crops.
Highlights
Carotenoids are natural pigments that are indispensable to plants and humans, whereas the regulation of carotenoid biosynthesis by post-translational modification remains elusive
We identify a tomato E3 ubiquitin ligase, Plastid Protein Sensing really interesting new gene (RING) E3 ligase 1 (PPSR1), in a screening of the interacting proteins of SlUBC32, an E2 enzyme that has been shown in our previous work to be involved in fruit ripening[16]
We carried out split luciferase complementation imaging (LCI) assay, in which cLUC-PPSR1 and SlUBC32-nLUC were transiently coexpressed in leaves of tobacco (Nicotiana benthamiana)
Summary
Carotenoids are natural pigments that are indispensable to plants and humans, whereas the regulation of carotenoid biosynthesis by post-translational modification remains elusive. We show that a tomato E3 ubiquitin ligase, Plastid Protein Sensing RING E3 ligase 1 (PPSR1), is responsible for the regulation of carotenoid biosynthesis. PPSR1 affects the abundance of 288 proteins, including phytoene synthase 1 (PSY1), the key rate-limiting enzyme in the carotenoid biosynthetic pathway. Whether precursors of proteins in specific metabolic processes such as the carotenoid biosynthetic pathway are regulated by ubiquitination has not been defined. We identify a tomato E3 ubiquitin ligase, Plastid Protein Sensing RING E3 ligase 1 (PPSR1), in a screening of the interacting proteins of SlUBC32, an E2 enzyme that has been shown in our previous work to be involved in fruit ripening[16]. We demonstrate that PPSR1 recognizes the precursor of phytoene synthase 1 (PSY1), the main rate-limiting enzyme in the carotenoid biosynthetic pathway, and mediates its ubiquitination and degradation. Our study reveals a direct role for protein ubiquitination in the regulation of carotenoid biosynthesis
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