*Review* **The FtsHi Enzymes of** *Arabidopsis thaliana***: Pseudo-Proteases with an Important Function**

**Laxmi S. Mishra and Christiane Funk \***

**Abstract:** FtsH metalloproteases found in eubacteria, animals, and plants are well-known for their vital role in the maintenance and proteolysis of membrane proteins. Their location is restricted to organelles of endosymbiotic origin, the chloroplasts, and mitochondria. In the model organism *Arabidopsis thaliana*, there are 17 membrane-bound FtsH proteases containing an AAA+ (ATPase associated with various cellular activities) and a Zn2+ metalloprotease domain. However, in five of those, the zinc-binding motif HEXXH is either mutated (FtsHi1, 2, 4, 5) or completely missing (FtsHi3), rendering these enzymes presumably inactive in proteolysis. Still, homozygous null mutants of the pseudo-proteases FtsHi1, 2, 4, 5 are embryo-lethal. Homozygous *ftshi3* or a weak point mutant in *FTSHi1* are affected in overall plant growth and development. This review will focus on the findings concerning the FtsHi pseudo-proteases and their involvement in protein import, leading to consequences in embryogenesis, seed growth, chloroplast, and leaf development and oxidative stress management.

**Keywords:** AAA-type protease; *Arabidopsis thaliana*; FtsH metalloprotease; chloroplast; embryo lethal; leaf variegation; plastid biogenesis; protein import; oxidative stress
