Gene expression pattern for putative chloroplast localized COPII related proteins with emphasis on Rab related proteins

Abstract

Vesicle transport occurs in the cytosol through COPI, COPII and a clathrin coated vesicle system for transport of lipids and proteins to different subcellular compartments. All three systems consist of several different protein components to maintain a functional transport. In chloroplasts photosynthesis takes place in thylakoids. Thylakoids contain a large amount of lipids and proteins but none of these components are produced there. Transport of lipids occurs from the envelope membrane where they are produced and through the aqueous stroma before being directed to the thylakoids. Nuclear encoded proteins use distinct pathways for entering thylakoids after import into chloroplasts. Transport of lipids through stroma requires either lipid transfer proteins, association between the envelope and the thylakoid membrane, or a vesicle transport system similar to the cytosolic one. No evidence exists for lipid transfer proteins in chloroplasts, nor for a consistent association between the envelope and the thylakoid membrane. However, vesicle transport has support from e.g., biochemical and genetics data as well as transelectron microscopy data. Moreover, a recent bioinformatics study revealed putatively COPII related proteins to be chloroplast localized in Arabidopsis and thus function in vesicle transport in chloroplasts. Here we present gene expression profiles of these putatively COPII related chloroplast localized proteins using Genevestigator (https://www.genevestigator.com/gv/) with special emphasis on Rab related proteins since they represent several stage of vesicle transport e.g., uncoating, tethering and fusion.

Vesicles Are Persistent Features of Different Plastids

“…The suggestion of vesicle transport of chloroplasts as an ongoing process to build and/or maintain inner membranes rather than rare incidents raises the question of when vesicles are most frequent. A clue might be given by the suggested COPII-like proteins, which appear to be expressed throughout the plant's life except during senescence (72). Among these, CPRabA5e appears to be mostly expressed during germination (13).…”

Chloroplast vesicle transport

“…CPRabA5e shows expression throughout the plant life cycle but has its highest expression during seed germination and the seedling stages (Alezzawi et al 2014 ; Karim et al 2014 ). The expression pattern is similar to the one found for CPSAR1 (Garcia et al 2010 ) and supports the presence of vesicles at all developmental stages.…”

The puzzle of chloroplast vesicle transport – involvement of GTPases

“…The latter (also known as ARA6 in Arabidopsis , or RAB5 according to human Rab nomenclature) is unique to plants, and reportedly involved in endosomal transport and modulation of the assembly of SNARE-related complexes ( Ebine et al, 2011 , 2012 ). Preliminary data obtained using an ARA6/RabF1 specific antibody have verified the presence of CPRabF1 in both the envelope and thylakoids of chloroplasts, implying that it has dual localization ( Alezzawi, 2014 ). However, the precise role of CPRabF1 in vesicle transport in chloroplasts requires further elucidation.…”