Proteolysis is considered as a crucial factor determining the proper development of the plant and its efficient functioning in variable environmental conditions. The role of proteases in protein quality control and protein turnover processes is well documented. The results of studies performed in recent years reveal; however, that proteolytic enzymes also participate in signal transduction pathways by releasing membrane-anchored transcription factors in the process known as regulated intramembrane proteolysis (RIP). The first described intramembrane protease was identified in human cells in 1997. In turn, the first plant intramembrane protease was identified in 2005, in Arabidopsis thaliana. To date, most studies concerning the RIP process in plants have been performed on this model plant. The knowledge concerning the potential physiological role of RIP is very limited. However, continuously accumulating information concerning this issue indicates that RIP, like the other proteolytic mechanisms, has a significant effect on plant ontogenesis, acclimatization and fertility. The aim of this article is to gather and systemize the present knowledge concerning the intramembrane proteases in A. thaliana.

Cx+c -total carotenoids; CAO -chlorophyllide a oxygenase; Chl -chlorophyll; EGY1 -ethylene-dependent gravitopismdeficient and yellow green 1; Fv/Fm -maximal quantum yield of PSII photochemistry; S2P -site-2 protease; WT -wild type.

Unfortunately, two reference citations were published incorrectly in the original publication of the article. In the last section before the Conclusion part, the 2nd and 3rd sentence should read as:Studies performed on spp heterozygotes indicate that the protein is involved in pollen development and germination (Han et al. 2009). The SPPL1, SPPL2 and SPPL3 transcripts were detected in the tissues, roots, rosette leaves, cauline leaves, stems, flower-bud clusters, siliques and dry seeds (Tamura et al. 2008). The significant accumulation of all three transcripts was, however, observed during seed germination.The online version of the original article can be found under

Degradation of chloroplast proteins within the organelle is supported by the observation that chloroplasts contain several proteases of the ClpP, FtsH, Deg, and Lon families. Clp proteases were among the first identified chloroplasts’ proteases and may play an important role during chloroplast biogenesis. Some members of the ClpP family (i.e., nclpP3 and nclpP5) are up-regulated during senescence, whereas the expression of other Clp proteases is constitutive, with no changes during leaf ontogeny. Interestingly, the mRNA levels of erd1, a Clp regulatory subunit are up-regulated during senescence of Arabidopsis thaliana leaves, but the levels of the corresponding ERD1 protein decline. Homologs of the bacterial FtsH protease are also found in plastids. At least 12 FtsH proteases have been identified in Arabidopsis thaliana, and some of them may play roles in thylakoid protein degradation. An FtsH protease is involved in the breakdown of the 23-kDa fragment of the D1 protein of the PSII reaction centre, which is formed upon photooxidative damage. Chloroplast DegP and FtsH proteases seem to cooperate in D1 degradation during photoinhibition, and it seems likely that they might also be responsible for D1 degradation during senescence. In vitro studies with thylakoids isolated from knock-out lines for FtsH6 have implicated the involvement of this protease in LHCII degradation during senescence. Other FtsH subunits may function in chloroplast biogenesis rather than senescence. In this article, we show which proteases are involved in the degradation of chloroplast proteins. We will focus on both: intrachloroplast and non-chloroplast proteases and their mechanism of the process.