Figure 6.

A Model for the Role of PAS Proteins and VLCFAs in Plant Cell Differentiation.

Fatty acid elongation requires long-chain fatty acyl-CoA (C_n LCFA-CoA) of n carbons and malonyl-CoA produced by the acetyl-CoA carboxylase PAS3. Elongation occurs in the ER membrane with four sequential reactions (boxed enzymes) to eventually produce very-long-chain fatty acyl-CoA of n+2 carbons (C_n+2 VLCFA-CoA). PAS1, by its association with elongase enzymes (dashed arrows), is required for fatty acid elongation. The role of VLCFA-CoA on plant development is most probably associated with the synthesis of membrane sphingolipids with long-chain bases (LCBs). Sphingolipids have been described to be involved in membrane trafficking and cell polarity, which are key determinants of cell differentiation.