Dual targeting of a mature plastoglobulin/fibrillin fusion protein to chloroplast plastoglobules and thylakoids in transplastomic tobacco plants

Abstract

Plastoglobules (PG) are lipid droplets in chloroplasts and other plastid types having important functions in lipid metabolism. Plastoglobulins (PGL) also known as fibrillins (FBN) are evolutionary conserved proteins present at the PG surface but also to various extents at the thylakoid membrane. PGLs are thought to have structural functions in PG formation and maintenance. The targeting of an Arabidopsis PGL (PGL34) to PG required the full protein sequence with the exception of a short C-terminal stretch. This indicated that PGL targeting relies on correct folding rather than a discrete sequence. PGLs lack strongly hydrophic regions and may therefore extrinsically associate with PG and thylakoid membranes via interaction with hydrophilic headgroups of surface lipids. Here, we report on the expression of the Arabidopsis plastoglobulin of 35kD (PGL35 or FBN1a) expressed as a mature protein fused to HIVp24 (human immunodeficiency virus capsid particle p24) or HCV (hepatitis C virus core protein) in transplastomic tobacco. A PGL35-HIVp24 fusion targeted in part to plastoglobules but a larger proportion was recovered in the thylakoid fraction. The findings indicate that transplastomic PGL35-HIVp24 folded correctly after its synthesis inside the chloroplast and then dually targeted to plastoglobules as well as thylakoid membranes.

Occurrence of plastidial triacylglycerol synthesis and the potential regulatory role of AGPAT in the model diatom Phaeodactylum tricornutum

“…Except of changes in the occurrence of numerous plastoglobuli in the plastid, no other significant anatomical changes were observed. Plastoglobuli are the plastidial compartment storing lipids that were found in some higher plants to be increased during TAG accumulation and adhered to thylakoid membranes [41–44]. The findings suggested the existence of plastidial located TAG synthesis which resulted in the TAG accumulation in the plastid.…”

The role of plastoglobules in thylakoid lipid remodeling during plant development

“…Regarding FBN distribution between PG and thylakoids, Lundquist et al have suggested that the intrinsic hydrophobicity and isoelectric point of FBN influence their localization to PG [20]. Moreover, it was demonstrated that the nearly entire sequence of FBN7a [147] or FBN1a [148] is required to target recombinant proteins to PG. Lipid remodeling requires molecular communication between PG and thylakoids that with great likelihood implicate their contact sites.…”

Efficient expression of nuclear transgenes in the green alga Chlamydomonas: synthesis of an HIV antigen and development of a new selectable marker

“…As P24 is expected to be a crucial component of any future AIDS vaccine (Obregon et al 2006 ), enormous efforts have been undertaken to develop expression strategies for the high-yield and cost-effective production of recombinant P24 protein (Meyers et al 2008 ). Proof-of-concept studies in tobacco have shown that the protein can be expressed from the nuclear genome of plants (Zhang et al 2002 ; Obregon et al 2006 ) and, much more efficiently, from the plastid genome (Zhou et al 2008 ; McCabe et al 2008 ; Shanmugabalaji et al 2013 ). Importantly, several immunogenicity studies with tobacco-derived P24 protein demonstrated elicitation of T cell responses in experimental animals (e.g., Meyers et al 2008 ; Gonzalez-Rabade et al 2011 ).…”