Solute channels of the outer membrane: from bacteria to chloroplasts

Chloroplasts, unique organelles of plants, originated from endosymbiosis of an ancestor of today's cyanobacteria with a mitochondria-containing host cell. It is assumed that the outer envelope membrane, which delimits the chloroplast from the surrounding cytosol, was thus inherited from its Gram-negative bacterial ancestor. This plastid-specific membrane is thus equipped with elements of prokaryotic and eukaryotic origin. In particular, the membrane-intrinsic outer envelope proteins (OEPs) form solute channels with properties reminiscent of porins and channels in the bacterial outer membrane. OEP channels are characterised by distinct specificities for metabolites and a quite peculiar expression pattern in specialised plant organs and plastids, thus disproving the assumption that the outer envelope is a non-specific molecular sieve. The same is true for the outer membrane of Gram-negative bacteria, which functions as a permeability barrier in addition to the cytoplasmic membrane, and embeds different classes of channel pores. The channels of these prokaryotic prototype proteins, ranging from unspecific porins to specific channels to ligand-gated receptors, are exclusively built of P-barrels. Although most of the OEP channels are formed by P-strands as well, phylogeny based on sequence homology alone is not feasible. Thus, the comparison of structural and functional properties of chloroplast outer envelope and bacterial outer membrane channels is required to pinpoint the ancestral OEP `portrait gallery'

Imaging and analysis of mitochondrial dynamics in living cells.

One of the most striking features of plant mitochondria when visualized in living tissue is their dynamism. The beauty of cytoplasmic streaming, driving, and being driven by the motility of mitochondria and other small organelles belies the complexity of the process. Equally, capturing that dynamism and investigating the genes, proteins, and mechanisms underpinning the processes using molecular cell biology and bioimaging is a complex process. It requires the generation of fluorescent protein constructs, stable transgenic plants sometimes expressing multiple fusions, and generation of mutants, even before one is ready for analytical experimentation. Here, we describe some of the key tools and methods necessary to investigate plant mitochondrial dynamics

Plant specific Preprotein and Amino Acid Transporter Proteins are required for tRNA import into mitochondria

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