Several geranylgeranyl diphosphate synthase isoforms supply metabolic substrates for carotenoid biosynthesis in tomato

Abstract

Geranylgeranyl diphosphate (GGPP) produced by GGPP synthase (GGPPS) serves as a precursor for many plastidial isoprenoids, including carotenoids. Here we show that five different GGPPS isoforms exist in tomato (Solanum lycopersicum). From these, SlGGPPS1, 2 and 3 (or SlG1-3 in short) produce GGPP in plastids and exhibit similar kinetic parameters. Phytoene synthase (PSY) converts GGPP into phytoene, the first committed intermediate of the carotenoid pathway. Gene expression and co-expression network analyses showed a preferential association of individual GGPPS and PSY isoforms in processes linked to carotenoid biosynthesis such as root mycorrhization, seedling deetiolation and fruit ripening. Co-immunoprecipitation experiments showed that SlG2, but not SlG3, physically interacts with PSY proteins. By contrast, CRISPR-Cas9 mutants defective in SlG3 showed a stronger impact on carotenoid levels and derived metabolic, physiological and developmental phenotypes that those impaired in SlG2. Double mutants with a simultaneous knockout of both genes could not be found. Our work demonstrates that the bulk of GGPP production in tomato chloroplasts and chromoplasts relies on two cooperating GGPPS paralogs, unlike other plant species such as Arabidopsis thaliana, rice or pepper, which produce their essential plastidial isoprenoids using a single GGPPS isoform.