This press release is available in German.
Chloroplasts, the plant cell's green solar power generators, were once living beings in their own right. This changed about one billion years ago, when they were swallowed up but not digested by larger cells. Since then, they have lost much of their autonomy. As time went on, most of their genetic information found its way into the cell nucleus; today, chloroplasts would no longer be able to live outside their host cell. Scientists in Ralph Bock's team at the Max Planck Institute of Molecular Plant Physiology have discovered that chloroplast genes take a direct route to the cell nucleus, where they can be correctly read in spite of their architectural differences.
Cyanobacteria are among the oldest life forms, and appear to be the forerunners of green chloroplasts in plant cells. They do not possess a true cell nucleus, but their genetic substance is made up of the same four building blocks as that of humans, plants and animals. Therefore, the genes encoded in the chloroplast DNA can also be read in the cell nucleus; indeed, many genes that were still found in the cell organelles during early evolution are now located exclusively in the genome of the nucleus. How they made their way there has previously been unclear. Two mechanisms appeared likely: either direct transport in the form of DNA fragments from the chloroplasts to the nucleus or transport in the form of mRNA, which is then transcribed back into DNA.
The direct transfer of DNA appears to predominate in the chloroplasts, but this pathway raises two problems. The first problem lies in the promoters, the DNA sequences which ensure that genes are recognised as such. They are located upstream of the genes and recruit proteins that are required for transcription of the genes. However, promoters from chloroplasts are not recognised as such by the proteins in the nucleus, so that the DNA reading machinery shoul
|Contact: Professor Dr. Ralph Bock|