Rab geranylgeranyl transferase activity is required for proper sterol biosynthesis in Arabidopsis thaliana.

In all eukaryotic cells, protein prenylation and cytoplasmic isoprenoid biosynthesis pathways leading to sterols, dolichols, and other isoprenoid compounds share a common precursor pool of isopentenyl diphosphate and the isomeric dimethylallyl diphosphate. Despite this, little is known about the interplay between these processes. Here we ask whether perturbation of protein prenylation in plants influences isoprenoid biosynthesis in the endoplasmic reticulum, and in particular if it affects sterol and dolichol biosynthesis. We use an Arabidopsis thaliana mutant with defects in the Rab geranylgeranyl transferase as a viable model of protein hypoprenylation, and we show that sterol and dolichol content is significantly elevated in the mutant plants. Also sterol composition is changed: cholesterol content is increased and some atypical sterol pathway intermediates are accumulating. Our results show that plant sterol biosynthesis involves high levels of crosstalk between pathway branches than previously reported and receives regulatory input from protein prenylation pathways.