PLASTID RNA POLYMERASES AND NUCLEAR-ENCODED PROTEINS ASSOCIATED WITH THEM IN ARABIDOPSIS THALIANA

The left part of the figure depicts the processes during skotomorphogenesis (growth in the dark), while the right part depicts the processes during photomorphogenesis (growth after shift to light). The genetic compartments involved (nucleus, plastids, mitochondria) are indicated. Plastids in the dark (etioplasts) contain a prolamellar body (PB), while chloroplasts in the light contain a thylakoid membrane system (Thy). Protein components acting in gene expression and regulation are given as circles. Labelling follows the abbreviations given in the text. For functional details and regulatory context also refer to text.
A heterozygous progeny of pap7-1/ptac14 (SAIL_566_F06; upper row) and pap8-1/ptac6 (Salk_024431; bottom row) were grown on ½ MS-media supplemented with sucrose. Pictures on the left were taken from 8 days old-seedlings grown on ½ MS-media, containing 1% sucrose with a light intensity of ~20 µE continuous white light at 21°C; pictures on the right were taken after 9 weeks growth on ½ MS-media, containing 3% sucrose with a light intensity of 8-12 µE white light (8 h light/ 16 h darkness) at 21°C.

from Monique Liebers and Thomas Pfannschmidt

 

Plastids are typical organelles of plant cells. Like mitochondria they are of endosymbiotic origin exhibiting still many features of their prokaryotic ancestry. However, during the establishment of endosymbiosis the former cyanobacteria-like ancestor was largely re-shaped with respect to gene and protein content. This included the addition of many eukaryotic factors to the prokaryotic machineries providing the nucleus of the host cell the control over the functions of the endosymbiont. A typical example for this evolutionary re-shaping is the plastid transcription machinery that is composed of bacterial, phage-type and eukaryotic components. Here, we summarize the current state of knowledge about structure and function of plastid RNA polymerases and their corresponding involvement in light-dependent seedling development. Special emphasis is given to a group of proteins associated to the plastid-encoded polymerase (PEP). These PEP-associated proteins (PAPs) and their corresponding inactivation mutants provide highly interesting tools for the dissection of the very early steps of chloroplast biogenesis, a process for which molecular regulators are largely unknown.