A mutant of the Arabidopsis thaliana TOC159 gene accumulates reduced levels of linolenic acid and monogalactosyldiacylglycerol
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- 作者：Meshack Afitlhile ; Samantha Workman ; Kayla Duffield ; Danielle Sprout ; Mark Berhow
- 关键词：Arabidopsis thaliana ; Fad5 ; MGDG ; MGD1 synthase ; ppi2 ; 16 ; 3
- 刊名：Plant Physiology and Biochemistry
- 出版年：December, 2013
- 年：2013
- 卷：73
- 期：Complete
- 页码：344-350
- 全文大小：903 K
文摘
Previous studies have shown that a mutant of Arabidopsis that lacks the Toc159 receptor is impaired in chloroplast biogenesis. The mutant is referred as plastid protein import 2 or ppi2 and has an albino phenotype due to its inability to import the photosynthetic proteins. In this study, we measured fatty acid composition and transcript levels of plastid-localized fatty acid desaturases in the wild type and ppi2 mutant. The objective was to evaluate whether the Toc159 receptor was critical in the import of lipid-synthesizing enzymes. The ppi2 mutant accumulated decreased levels of oleic acid (18:1) and 伪-linolenic acid (18:3). The mutant accumulated drastically reduced amounts of the chloroplast lipid monogalactosyldiacylglycerol (MGDG), which contains more than 80% of 18:3. The expression of genes that encode stearoyl-ACP desaturase and MGD1 synthase were down-regulated in the ppi2 mutant, and this corresponded to decreased levels of 18:1 and MGDG, respectively. We conclude that in the ppi2 mutant the impaired synthesis of MGDG resulted in decreased amounts of 18:3. The mutant however, had a 30-fold increase in fad5 transcript levels; this increase was mirrored by a 16- to 50-fold accumulation of hexadecatrienoic acid (16:3), a fatty acid found exclusively in MGDG. Taken together, these data suggest that the Toc159 receptor is required in the import of stearoyl-ACP desaturase and MGD1 synthase into the chloroplasts. Since the expression of fad5 gene was up-regulated in the ppi2 mutant, we propose that fad5 desaturase is imported into plastids through the atToc132/atToc120 protein import pathway.