Membrane proteins in the outer mebrane of plastids and mitochondria

Channels of the plastid and mitochondrial outer membranes
facilitate the turnover of molecules and ions via these membranes.
Although channels have been studied many questions pertaining to
the whole diversity of plastid and mitochondrial channels in
Arabidopsis thaliana and Pisum sativum remain unanswered. In this
thesis I studied OEP16, OEP37 and VDAC families in two model
plants, in Arabidopsis and pea. The Arabidopsis OEP16 family
represents four channels of α-helical structure, similar to the pea
OEP16 protein. These channels are suggested to transport amino
acids and compounds with primary amino groups. Immunoblot analysis,
GFP/RFP protein fusion expression, as well as proteomic analysis
showed that AtOEP16.1, AtOEP16.2 and AtOEP16.4 are located in the
outer envelope membrane of plastids, while AtOEP16.3 is in
mitochondria. The gene expression and immunoblot analyses revealed
that AtOEP16.1 and AtOEP16.3 proteins are highly abundant and
ubiquitous; expression of AtOEP16.1 is regulated by light and cold.
AtOEP16.2 is highly expressed in pollen, seeds and seedlings.
AtOEP16.4 is a low expressed housekeeping protein. Single knockout
mutants of AtOEP16.1, AtOEP16.2 and AtOEP16.4, and double mutants
of AtOEP16 gene family did not show any remarkable phenotype.
However, macroarray analysis of Atoep16.1-p T-DNA mutant revealed
10 down-regulated and 6 up-regulated genes. In contrast to the
α-helical OEP16 proteins, the OEP37 and VDAC proteins are of
β-barrel structure. The PsOEP37 and AtOEP37 channel proteins form a
selective barrier in the outer envelope of chloroplasts.
Electrophysiological studies in lipid bilayer membranes showed that
the PsOEP37 channel is permeable for cations. Specific expression
profiles showed that AtOEP37 and PsOEP37 are highly expressed in
the entire plant. The isolated PsVDAC gene encodes a protein, which
is located in mitochondria. In Arabidopsis gene database, five
Arabidopsis genes, which code for VDAC-like proteins were
announced. One gene was not detected, whereas four of these genes
expressed in leaves, roots, flower buds and pollen.