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Plant Cell Physiol. 2015 Jul;56(7):1374-87. doi: 10.1093/pcp/pcv056. Epub 2015 Apr 22.

Ubiquitin-Mediated Proteasomal Degradation of Oleosins is Involved in Oil Body Mobilization During Post-Germinative Seedling Growth in Arabidopsis.

Author information

1
INRA, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS 3559, Saclay Plant Sciences, RD10, F-78026 Versailles, France AgroParisTech, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS 3559, Saclay Plant Sciences, RD10, F-78026 Versailles, France.
2
INRA, UMR 1319, PAPPSO, F-78350 Jouy-en-Josas, France.
3
INRA, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS 3559, Saclay Plant Sciences, RD10, F-78026 Versailles, France AgroParisTech, Institut Jean-Pierre Bourgin, UMR 1318, ERL CNRS 3559, Saclay Plant Sciences, RD10, F-78026 Versailles, France sabine.dandrea@versailles.inra.fr.

Abstract

In oleaginous seeds, lipids--stored in organelles called oil bodies (OBs)--are degraded post-germinatively to provide carbon and energy for seedling growth. To date, little is known about how OB coat proteins, known as oleosins, control OB dynamics during seed germination. Here, we demonstrated that the sequential proteolysis of the five Arabidopsis thaliana oleosins OLE1-OLE5 begins just prior to lipid degradation. Several post-translational modifications (e.g. phosphorylation and ubiquination) of oleosins were concomitant with oleosin degradation. Phosphorylation occurred only on the minor OLE5 and on an 8 kDa proteolytic fragment of OLE2. A combination of immunochemical and proteomic approaches revealed ubiquitination of the four oleosins OLE1-OLE4 at the onset of OB mobilization. Ubiquitination topology was surprisingly complex. OLE1 and OLE2 were modified by three distinct and predominantly exclusive motifs: monoubiquitin, K48-linked diubiquitin (K48Ub(2)) and K63-linked diubiquitin. Ubiquitinated oleosins may be channeled towards specific degradation pathways according to ubiquitination type. One of these pathways was identified as the ubiquitin-proteasome pathway. A proteasome inhibitor (MG132) reduced oleosin degradation and induced cytosolic accumulation of K48Ub(2)-oleosin aggregates. These results indicate that K48Ub(2)-modified oleosins are selectively extracted from OB coat and degraded by the proteasome. Proteasome inhibition also reduced lipid hydrolysis, providing in vivo evidence that oleosin degradation is required for lipid mobilization.

KEYWORDS:

Arabidopsis; Oil body; Oleosin; Proteasome; Seed; Ubiquitin-mediated degradation

PMID:
25907570
DOI:
10.1093/pcp/pcv056
[Indexed for MEDLINE]

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