The Pex16p Homolog SSE1 and Storage Organelle Formation in Arabidopsis Seeds

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Abstract
Mature Arabidopsis seeds are enriched in storage proteins and lipids, but lack starch. In the shrunken seed 1(sse1) mutant, however, starch is favored over proteins and lipids as the major storage compound. SSE1 has 26 percent identity with Pex16p in Yarrowia lipolytica and complementspex16 mutants defective in the formation of peroxisomes and the transportation of plasma membrane– and cell wall–associated proteins. In Arabidopsis maturing seeds, 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.