Chloroplast Members of the S2P Proteases Family, AraSP and AtS2P2, May Have a Functional Relationship in Promoting Plant Growth

Site-2-protease (S2P) homologs in Arabidopsis thaliana, AraSP and AtS2P2, which belong to the family of intramembrane cleavage proteases, play a pivotal roles in processes related to plant growth and their response to abiotic and biotic stresses. Our study revealed that the knockout either the AraSP or AtS2P2 genes alone did not affect the growth or development of the corresponding GABI-kat transgenic lines, as single mutants, GK_848F10 (arasp) and GK_553F11 (ats2p2), exhibited normal growth and development similar to the wild type, at all growth stages. Photosynthetic complexes composition and their photosynthetic capacity were unaffected in single mutants and were similar to the wild-type, despite a significant reduction in LHCb2 polypeptide content of the light-harvesting complex II. However, introducing the double arasp/ats2p2 mutation into A. thaliana caused a pleiotropic effect in transgenic plants, manifested by a significant decrease in photosynthetic proteins content and impaired photoprotective mechanisms. These changes were crucial for plant development, including seed formation. Our findings indicate that the AraSP and AtS2P2 proteins might have functional redundancy or overlap between their functions and could be implicated in a variety of processes, ensuring the proper functioning of photosystems and plant development.