The pex16p homolog SSE1 and storage organelle formation in Arabidopsis seeds

Mature Arabidopsis seeds are enriched in storage proteins and lipids, but l ack starch. In the shrunken seed 1 (sse1) mutant, however, starch is favore d over proteins and lipids as the major storage compound. SSE1 has 26 perce nt identity with Pex16p in Yarrowia lipolytica and complements pex16 mutant s defective in the formation of peroxisomes and the transportation of plasm a membrane- and cell wall-associated proteins, In Arabidopsis maturing seed s, SSE1 is required for protein and oil body biogenesis, both of which are endoplasmic reticulum-dependent. Starch accumulation in sse1 suggests that starch formation is a default storage deposition pathway.