Several chloroplast proteases have been characterized in recent years. The ATP-dependent chloroplast proteases Clp and FtsH stand out because they form multi-subunit complexes consisting of different gene products. Surprisingly, both green and non-green plastids appear to contain a similar soluble Clp core proteolytic complex, consisting of five ClpP proteases, their non-catalytic ClpR homologs, and two ClpS homologs that have unknown function. Analyses of single and double FtsH1, FtsH2, FtsH5 and FtsH8 mutants, and overexpression of FtsH proteins in these Arabidopsis thaliana mutants show partial redundancies within pairs of closely related FtsH thylakoid proteins. The presence of at least one member of each pair is essential for functional accumulation. Other chloroplast proteases have also been identified recently. Future challenges include the identification of substrate recognition mechanisms and elucidating the role of proteases in chloroplast biogenesis and function.
Bibliographical noteFunding Information:
Research in the Adam laboratory was supported by grants from the Israel Science Foundation (no. 122/00), the US–Israel Binational Agricultural Research and Development Fund (US-3033-98), and the US–Israel Binational Science Foundation (no. 9800050). Research on chloroplast protease in the van Wijk laboratory is supported by grants from the US National Science Foundation (NSF-MCB-0343444) and The US Department of Energy (DE-FG02-04ER15560). Further support was obtained by a joint grant to both groups from the US–Israel Binational Science Foundation (no. 2003302). We thank Daniel Ripoll from the Cornell Computational Biology Service Unit for homology modeling of the Clp complexes.