Poster: Lipids & Related Molecules

Abs # 866: Role of Caleosins in oil body biogenesis

Presenter:	Poxleitner, Marianne K., marip@mail.wsu.edu
Authors	Poxleitner, Marianne K. (A)   Rogers, John C. (A)
Affiliations:	(A): Washington State Universtiy, Institute of Biological Chemistry

Caleosin and oleosin are embedded in the half unit membranes of oil bodies in many plant seeds. Functionally, oleosin is believed to coat the oil body surface and thereby prevent coalescence of adjacent oil bodies. Both proteins have similar proposed structures including N-and C-terminal cytosolic ends, and long hydrophobic internal segments with centrally located proline knot motifs. Caleosin’s function in oil bodies has yet to be determined, but it has been hypothesized that it is involved in oil body biogenesis from the ER. Caleosins are a multigene family in Arabidopsis, with a single isoform, Clo1, predominantly expressed in seeds. We find that two separate insertional knockout mutants for Clo1 have no visible phenotype and produce viable seeds. The absence of Clo1 expression was confirmed by Western Blots and immunofluorescence, with mutant seeds having normal embryo and oil body morphology as well as normal expression of oleosin. Thus, Clo1 has no essential role in oil body biogenesis. We further sought clues for the function of caleosin by comparing its distribution in Brassica napus root tip cells. These studies demonstrate that both oleosin and caleosin are present in almost all cell types and co-localize. Thus, all data so far indicate that caleosins are not markers for a unique type of oil body. When another member of the caleosin gene family, Clo2, is insertionally mutated in Arabidopsis, the mutant phenotype presents as slow growing seedlings which eventually mature and bear seed. Studies to determine the effect of the knockout on oil body and vacuole morphology are underway.