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The Holy Grail of chloroplast gene expression ...

Chloroplast RNA metabolism is characterized by a multitude of RNA processing events, including RNA cleavage, RNA editing and RNA splicing. This complexity is paralleled by the large number of RNA processing factors identified thus far. Several families of nuclear-encoded RNA binding proteins have evolved to specifically serve plant organellar RNA metabolism. More than 150 factors have been described to be required for chloroplast RNA metabolism alone. In addition to this wealth of nuclear-encoded factors, there is a few chloroplast-encoded proteins with roles in RNA metabolism (ribosomal subunits; RNA polymerase subunits; splicing factor MatK).

The plethora of known and postulated factors is in strong contrast to the paucity of data on their role for chloroplast gene regulation (The term ‘regulation’ is used here exclusively to describe processes that alter the output of gene product in response to a signal. Often, ‘regulation’ is used inaccurately for factors that are involved in an RNA-processing event, but for which an impact on the rate of gene expression has not been demonstrated.). While it has been demonstrated that many RNA processing factors are essential for chloroplast development, it has not been shown in higher plants whether any of these factors are limiting for the output of chloroplast gene expression under natural conditions. We are interested in uncovering steps and factors that limit the output of chloroplast gene expression.

Currently, we focus on three main projects:

1.   Analysis of chloroplast RNA binding proteins
a.   cpRNPs as regulators of chloroplast gene expression
b.   Mechanistic insights into PPR proteins
c.   The chloroplast splicing factor MatK

2.   Short, non-coding plant organellar RNAs

3.   Ribonomics of the chloroplast basal expression apparatus: ribosomes and RNA Polymerases