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. However, knowledge accumulated in the last several years has revealed another, previously unknown mechanism of proteolytic control – regulated intramembrane proteolysis (RIP). RIP is performed by intramembrane proteases – integral membrane proteins able to hydrolyze a transmembrane helix of their substrates and release them from the membrane. This recently identified class of proteases occurs ubiquitously in all living organisms from Bacteria through Archaea to Eukarya. The first described intramembrane protease was identified in human cells in 1997, and in 2005, in Arabidopsis thaliana, the first plant intramembrane protease was identified. To date, four families of intramembrane proteases have been identified in Arabidopsis thaliana: site-2 proteases (S2Ps), rhomboids, presenilins and signal peptide peptidases. The knowledge concerning the potential physiological role of plant intramembrane proteases is very limited. Continuously accumulating data indicate, however, that their role in development should not be underestimated. Many studies indicate that intramembrane protease performs crucial functions in providing plant fertility, proper chloroplast biogenesis and photosynthetic process efficiency. In most cases the mechanisms leading from gene mutation to phenotypic changes and development aberrations have not been discovered yet. We demonstrated, that Egy2 –intramembrane zinc metalloprotease located in chloroplasts – participates in regulation of chloroplast genes, encoding crucial photosystem II proteins: PsbA, PsbD and PsbC. Furthermore, according to our comparative genomic analysis, several inactive rhomboid-like proteins share relatively high sequence identity, highly conserved primary structure motifs and domain architecture what may indicate that they perform an important physiological function. The role of this proteins remains, however, unknown. This makes the plant transmembrane proteases and they relatives extremely interesting field for future research.
This work was supported by the Polish National Science Center based on decision number DEC-2014/15/B/NZ3/00412