Poster: Organelle Biogenesis

Abs # 1172: Peroxin ortholog Pex10p exists in ER of Arabidopsis cells and in plastids of BY-2 cells: Do these locales reflect its function in peroxisomal biogenesis?

Presenter:	Heinze, Michael , Michael.Heinze@asu.edu
Authors	Heinze, Michael  (A)   Trelease, Richard N (A)
Affiliations:	(A): Arizona State University, Department of Plant Biology

Pex10p is one of 24 known peroxins, which are proteins involved variously in peroxisomal biogenesis. In human and yeast cells, Pex10p, is integrated into the peroxisomal boundary membrane and functions in the posttranslational acquisition of matrix proteins. A putative Arabidopsis homolog AtPex10p with two apparent transmembrane domains was predicted to function in boundary membranes of plant peroxisomes. Repeated and varied attempts, however, have failed to reveal any colocalization of AtPex10p or NtPex10p with any peroxisomal membrane or matrix marker protein via immunofluorescence or electron microscopy or via cell fractionation using cultured Arabidopsis or BY-2 cells. Instead, AtPex10p was localized to a reticular immunofluorescence compartment in vivo, to rough ER microsomes in Mg²⁺-shifted fractions (immunoblot and immunogold microscopy), and to rough ER sheets in situ (immunogold microscopy). NtPex10p, surprisingly, was localized to plastids via immunofluorescence and electron immunogold microscopy (stroma). Overexpressed epitope-tagged AtPex10p did not sort to peroxisomes, but accumulated in the reticular immunofluorescence compartment in both cell types. The collective results indicate that the plant Pex10p ortholog does not function in peroxisomes as in other organisms, but exerts its function within a subdomain of ER (reticular compartment), probably in the formation/differentiation of peroxisomes from segments of ER called peroxisomal ER (pER). The plastid NtPex10p may participate in the production of fatty acids transported to peroxisomes or lipid bodies and used at the site of pER. NSF grant MCB-0091826 to RNT.