An essential role of a TatC homologue of a ΔpH- dependent protein transporter in thylakoid membrane formation during chloroplast development in Arabidopsis thaliana

Abstract

At least three transport systems function in targeting nuclearencoded chloroplast proteins to the chloroplast thylakoid membrane. One of these systems requires a thylakoid pH gradient and is named the ⌬pH-dependent protein transport system. A similar ⌬pH export system of Escherichia coli contains four components, twin arginine translocation A (TatA), TatB, TatC, and TatE. TatC is a major component of the ⌬pH-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.

Disruption of phytoene desaturase gene results in albino and dwarf phenotypes in Arabidopsis by impairing chlorophyll, carotenoid, and gibberellin biosynthesis

“…Only undifferentiated proplastids were found in the mesophyll cells at all three developmental stages examined, while no thylakoid membrane system Figure 7C-D). Cells became increasingly vacuolated during development, which was also observed in another albino mutant apg2 [32]. These results indicated that proplastids in the mesophyll cells of the pds3 mutant were arrested at the undifferentiated stage and had lost the ability to develop into mature chloroplasts.…”

Suppressors of the Chloroplast Protein Import Mutant tic40 Reveal a Genetic Link between Protein Import and Thylakoid Biogenesis

“…The thylakoid targeting pathway component mutants cpsrp54-3 (WiscDsLox289_292B14), cpftsY-1 (SALK_049077), cpftsY-2 (SALK_112451), and secA-1 (SALK_063371) were also previously characterized (Asakura et al, 2008;Liu et al, 2010;Yu et al, 2012). To our knowledge, the hcf106 (SALK_020680) mutant has not been characterized before, but it does produce a similar albino phenotype to a previously reported mutant of another Tat pathway component, TatC (Motohashi et al, 2001), while the cpsrp43-2 (SAIL_783_F08) mutant (Sessions et al, 2002) was shown in this study to accumulate no detectable cpSRP43 protein.…”

The Peroxisome Deficient Arabidopsis Mutant sse1 Exhibits Impaired Fatty Acid Synthesis

“…Even in leaf tissues where photosynthesis provides most of the ATP and reducing power for fatty acid synthesis, exogenous sugar could serve as an alternative resource when photosynthesis is abolished. This is demonstrated by the fact that Arabidopsis albino mutants could grow to fairly normal size in tissue culture in the presence of exogenous sugar (Grevelding et al, 1996;Motohashi et al, 2001). Based on these rationales, we think it is unlikely that the dramatic reduction of oil content in sse1 is due solely to lack of photosynthesis.…”