New functions of the chloroplast Preprotein and Amino acid Transporter (PRAT) family members in protein import.
Plant cells contain distinct compartments such as the nucleus, the endomembrane system comprising the endoplasmic reticulum and Golgi apparatus, peroxisomes, vacuoles, as well as mitochondria and chloroplasts. All of these compartments are surrounded by 1 or 2 limiting membranes and need to import proteins from the cytosol. Previous work led to the conclusion that mitochondria and chloroplasts use structurally different protein import machineries in their outer and inner membranes for the uptake of cytosolic precursor proteins. Our most recent data show that there is some unexpected overlap. Three members of the family of preprotein and amino acid transporters, PRAT, were identified in chloroplasts that mediate the uptake of transit sequence-less proteins into the inner plastid envelope membrane. By analogy, mitochondria contain with TIM22 a related PRAT protein that is involved in the import of transit sequence-less proteins into the inner mitochondrial membrane. Both mitochondria and chloroplasts thus make use of similar import mechanisms to deliver some of their proteins to their final place. Because single homologs of HP20- and HP30-like proteins are present in algae such as Chlamydomonas, Ostreococcus, and Volvox, which diverged from land plants approximately 1 billion years ago, it is likely that the discovered PRAT-mediated mechanism of protein translocation evolved concomitantly with the secondary endosymbiotic event that gave rise to green plants.
Biologie Environnementale et Systémique (BEeSy); Université Joseph Fourier; LBFA; BP53F; Grenoble, France.
Claudia
C
Rossig
Biologie Environnementale et Systémique (BEeSy); Université Joseph Fourier; LBFA; BP53F; Grenoble, France.
Christiane
C
Reinbothe
Department of Biological Sciences; University of Toledo; Toledo, OH USA.
John
J
Gray
Biologie Environnementale et Systémique (BEeSy); Université Joseph Fourier; LBFA; BP53F; Grenoble, France.
Oscar
O
Valdes
Department of Crop and Soil Sciences; School of Molecular Biosciences; Center for Reproductive Biology; Washington State University; Pullman, WA USA.
Diter
D
von Wettstein
Biologie Environnementale et Systémique (BEeSy); Université Joseph Fourier; LBFA; BP53F; Grenoble, France.
Steffen
S
Reinbothe
D002736:Chloroplasts / Q000378:metabolism; D055786:Gene Knockout Techniques; D059828:Plant Cells / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011808:Quinone Reductases / Q000378:metabolism; D034622:RNA Interference
D010940:Plant Proteins; D011808:Quinone Reductases
Chloroplasts and mitochondria; Membrane transport; PRAT protein evolution; Protein translocation; TIC and TIM translocons at the inner chloroplast envelope and inner mitochondrial membrane; TOC and TOM translocons at outer chloroplast and outer mitochondrial membrane