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Complete maturation of the plastid protein translocation channel requires a type I signal peptidase.

Inoue K, Baldwin AJ, Shipman RL, Matsui K, Theg SM, Ohme-Takagi M - J. Cell Biol. (2005)

Bottom Line: Next, we show that disruption of a gene encoding plastidic SPase I (Plsp1) resulted in the accumulation of immature forms of Toc75, severe reduction of plastid internal membrane development, and a seedling lethal phenotype.These phenotypes were rescued by the overexpression of Plsp1 complementary DNA.Plsp1 appeared to be targeted both to the envelope and to the thylakoidal membranes; thus, it may have multiple functions.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Sciences, College of Agricultural and Environmental Sciences, University of California, Davis, CA 95616, USA. kinoue@ucdavis.edu

ABSTRACT
The protein translocation channel at the plastid outer envelope membrane, Toc75, is essential for the viability of plants from the embryonic stage. It is encoded in the nucleus and is synthesized with a bipartite transit peptide that is cleaved during maturation. Despite its important function, the molecular mechanism and the biological significance of the full maturation of Toc75 remain unclear. In this study, we show that a type I signal peptidase (SPase I) is responsible for this process. First, we demonstrate that a bacterial SPase I converted Toc75 precursor to its mature form in vitro. Next, we show that disruption of a gene encoding plastidic SPase I (Plsp1) resulted in the accumulation of immature forms of Toc75, severe reduction of plastid internal membrane development, and a seedling lethal phenotype. These phenotypes were rescued by the overexpression of Plsp1 complementary DNA. Plsp1 appeared to be targeted both to the envelope and to the thylakoidal membranes; thus, it may have multiple functions.

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Related in: MedlinePlus

Disruption of PLSP1 results in the accumulation of unprocessed forms of Toc75. Protein extracts of etiolated A. thaliana seedlings were analyzed by immunoblotting using antisera against the indicated plastidic proteins. m75, i75, and a 90-kD protein nonspecifically detected by the antisera (indicated with an asterisk) are indicated on the right side of the top row. Two protein bands slightly larger than 75 kD that were detected in plsp1-1 plants are indicated with arrowheads (lane 2). Bands corresponding to the intermediate and mature forms of OE33 and also a minor band larger than the mature form are indicated with the letters i, m, and an arrowhead, respectively, in the bottom row.
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fig3: Disruption of PLSP1 results in the accumulation of unprocessed forms of Toc75. Protein extracts of etiolated A. thaliana seedlings were analyzed by immunoblotting using antisera against the indicated plastidic proteins. m75, i75, and a 90-kD protein nonspecifically detected by the antisera (indicated with an asterisk) are indicated on the right side of the top row. Two protein bands slightly larger than 75 kD that were detected in plsp1-1 plants are indicated with arrowheads (lane 2). Bands corresponding to the intermediate and mature forms of OE33 and also a minor band larger than the mature form are indicated with the letters i, m, and an arrowhead, respectively, in the bottom row.

Mentions: To examine the effect of PLSP1 disruption on the processing and/or accumulation of Toc75, we analyzed proteins from etiolated seedlings by immunoblotting. As shown in Fig. 3, mutant plants mainly accumulated an 84-kD protein, which corresponds to the intermediate form of Toc75 as well as to several minor proteins of sizes larger than 75 kD (lane 2). In contrast, the complemented plants accumulated mature-sized Toc75 (Fig. 3, lane 3). The presence of the intermediate form in the complemented plants (Fig. 3, lane 3) may be caused by the ectopic expression of PLSP1 by the constitutive promoter. These data indicate that Plsp1 is required for proper maturation of Toc75. Previously, Toc75 was shown to be essential for embryogenesis (Baldwin et al., 2005). Together with the current data, we suggest that the immature forms of Toc75 can form protein translocation channels to support at least minimal development of plastids and, thus, embryogenesis.


Complete maturation of the plastid protein translocation channel requires a type I signal peptidase.

Inoue K, Baldwin AJ, Shipman RL, Matsui K, Theg SM, Ohme-Takagi M - J. Cell Biol. (2005)

Disruption of PLSP1 results in the accumulation of unprocessed forms of Toc75. Protein extracts of etiolated A. thaliana seedlings were analyzed by immunoblotting using antisera against the indicated plastidic proteins. m75, i75, and a 90-kD protein nonspecifically detected by the antisera (indicated with an asterisk) are indicated on the right side of the top row. Two protein bands slightly larger than 75 kD that were detected in plsp1-1 plants are indicated with arrowheads (lane 2). Bands corresponding to the intermediate and mature forms of OE33 and also a minor band larger than the mature form are indicated with the letters i, m, and an arrowhead, respectively, in the bottom row.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2171254&req=5

fig3: Disruption of PLSP1 results in the accumulation of unprocessed forms of Toc75. Protein extracts of etiolated A. thaliana seedlings were analyzed by immunoblotting using antisera against the indicated plastidic proteins. m75, i75, and a 90-kD protein nonspecifically detected by the antisera (indicated with an asterisk) are indicated on the right side of the top row. Two protein bands slightly larger than 75 kD that were detected in plsp1-1 plants are indicated with arrowheads (lane 2). Bands corresponding to the intermediate and mature forms of OE33 and also a minor band larger than the mature form are indicated with the letters i, m, and an arrowhead, respectively, in the bottom row.
Mentions: To examine the effect of PLSP1 disruption on the processing and/or accumulation of Toc75, we analyzed proteins from etiolated seedlings by immunoblotting. As shown in Fig. 3, mutant plants mainly accumulated an 84-kD protein, which corresponds to the intermediate form of Toc75 as well as to several minor proteins of sizes larger than 75 kD (lane 2). In contrast, the complemented plants accumulated mature-sized Toc75 (Fig. 3, lane 3). The presence of the intermediate form in the complemented plants (Fig. 3, lane 3) may be caused by the ectopic expression of PLSP1 by the constitutive promoter. These data indicate that Plsp1 is required for proper maturation of Toc75. Previously, Toc75 was shown to be essential for embryogenesis (Baldwin et al., 2005). Together with the current data, we suggest that the immature forms of Toc75 can form protein translocation channels to support at least minimal development of plastids and, thus, embryogenesis.

Bottom Line: Next, we show that disruption of a gene encoding plastidic SPase I (Plsp1) resulted in the accumulation of immature forms of Toc75, severe reduction of plastid internal membrane development, and a seedling lethal phenotype.These phenotypes were rescued by the overexpression of Plsp1 complementary DNA.Plsp1 appeared to be targeted both to the envelope and to the thylakoidal membranes; thus, it may have multiple functions.

View Article: PubMed Central - PubMed

Affiliation: Department of Plant Sciences, College of Agricultural and Environmental Sciences, University of California, Davis, CA 95616, USA. kinoue@ucdavis.edu

ABSTRACT
The protein translocation channel at the plastid outer envelope membrane, Toc75, is essential for the viability of plants from the embryonic stage. It is encoded in the nucleus and is synthesized with a bipartite transit peptide that is cleaved during maturation. Despite its important function, the molecular mechanism and the biological significance of the full maturation of Toc75 remain unclear. In this study, we show that a type I signal peptidase (SPase I) is responsible for this process. First, we demonstrate that a bacterial SPase I converted Toc75 precursor to its mature form in vitro. Next, we show that disruption of a gene encoding plastidic SPase I (Plsp1) resulted in the accumulation of immature forms of Toc75, severe reduction of plastid internal membrane development, and a seedling lethal phenotype. These phenotypes were rescued by the overexpression of Plsp1 complementary DNA. Plsp1 appeared to be targeted both to the envelope and to the thylakoidal membranes; thus, it may have multiple functions.

Show MeSH
Related in: MedlinePlus