Figure 9.

Osmotic stress modulates the input of MEP and MVA pathways to Dol synthesis. The biosynthetic origin of Dol-16 (and other dominating Dols, Dol-14, Dol-15, and Dol-17) changes upon osmotic stress, while that of Dol-21 (and other long-chain Dols, n > 18 and also Dol-13) remains unaffected. This implies that, upon osmotic stress, the oligoprenyl precursors synthesized by plastidial CPT and translocated to the cytoplasm are longer than those synthesized in control conditions. In contrast, the synthesis of long-chain Dols proceeds probably in a cellular compartment other than plastids/cytoplasm. Such activity is tentatively assigned to peroxisomal CPT, which probably utilizes an autonomous, MVA-dependent pool of IPP in concert with MEP-derived IPP imported to peroxisomes through plastid-peroxisome contact sites (Shai et al., 2016). Modulation of the intensity of export of plastidial MEP-derived IPP and possibly oligoprenyl diphosphates upon stress is depicted by cyan and white arrows, respectively.