An Essential Role of a TatC Homologue of a ΔpH-Dependent Protein Transporter in Thylakoid Membrane Formation during Chloroplast Development in Arabidopsis thaliana

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 98; no. 18; pp. 10499 - 10504
• Main Authors: Motohashi, Reiko, Nagata, Noriko, Ito, Takuya, Takahashi, Seiji, Hobo, Tokunori, Yoshida, Shigeo, Shinozaki, Kazuo
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 28-08-2001; National Acad Sciences; The National Academy of Sciences
• Subjects: Albinism; Amino Acid Sequence; Amino acids; apg2 gene; Arabidopsis - genetics; Arabidopsis - growth & development; Arabidopsis - metabolism; Arabidopsis Proteins; Arabidopsis thaliana; Base Sequence; Biological Sciences; Biological Transport, Active; Carrier Proteins - genetics; Carrier Proteins - metabolism; Chloroplasts; Chloroplasts - metabolism; DNA Transposable Elements - genetics; DNA, Plant - genetics; Escherichia coli; Escherichia coli - genetics; Escherichia coli - metabolism; Gels; Gene Expression; Genes; Genes, Plant; Hydrogen-Ion Concentration; Membrane Proteins - genetics; Membrane Proteins - metabolism; Molecular Sequence Data; Mutation; Plant Leaves - metabolism; Plant Proteins - genetics; Plant Proteins - metabolism; Plants; Plants, Genetically Modified; Plastids; Protein transport; Proteins; RNA, Messenger - genetics; RNA, Messenger - metabolism; RNA, Plant - genetics; RNA, Plant - metabolism; Sequence Homology, Amino Acid; TatA protein; TatB protein; TatC protein; TatE protein; Thylakoids; Tissue Distribution
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.181304598

At least three transport systems function in targeting nuclear-encoded chloroplast proteins to the chloroplast thylakoid membrane. One of these systems requires a thylakoid pH gradient and is named the ΔpH-dependent protein transport system. A similar ΔpH export system of Escherichia coli contains four components, twin arginine translocation A (TatA), TatB, TatC, and TatE. TatC is a major component of the ΔpH-dependent protein transporter in E. coli and functions in the translocation of tightly folded proteins across membranes. We have isolated four transposon-inserted albino mutants named albino and pale green 2 (apg2) from Arabidopsis thaliana and showed that the transposons were inserted into different sites of a single gene. The APG2 gene product (named cpTatC) has sequence similarity with bacterial TatC and contains six putative transmembrane domains, including bacterial TatC proteins and a transit peptide in its N terminus, apg2 mutants showed albino phenotypes and could not grow in soil. The apg2 plastids were highly vacuolated, lacked internal membrane structures and lamellae of the thylakoid membrane, and contained many densely stained globule structures, like undifferentiated proplastids. Immunoblot analysis detected no thylakoid membrane proteins such as D1, light-harvesting complex, and OE23 in apg2 plastids, whereas soluble proteins such as rubisco large and small subunits were not decreased. These results indicate an essential role of cpTatC in chloroplast development, especially in thylakoid membrane formation.