Nilsson Cederholm Stefan, Bäckman Hans G, Pesaresi Paolo, Leister Dario, Glaser Elzbieta
Department of Biochemistry and Biophysics, Stockholm University, 106 91 Stockholm, Sweden.
Plant Mol Biol. 2009 Nov;71(4-5):497-508. doi: 10.1007/s11103-009-9534-6. Epub 2009 Aug 23.
A novel peptidasome PreP is responsible for degradation of targeting peptides and other unstructured peptides in mitochondria and chloroplasts. Arabidopsis thaliana contains two PreP isoforms, AtPreP1, and AtPreP2. Here we have characterized single and double prep knockout mutants. Immunoblot analysis of atprep1 and atprep2 mutants showed that both isoforms are expressed in all tissues with the highest expression in flowers and siliques; additionally, AtPreP1 accumulated to a much higher level in comparison to AtPreP2. The atprep2 mutant behaved like wild type, whereas deletion of AtPreP1 resulted in slightly pale-green seedlings. Analysis of the atprep1 atprep2 double mutant revealed a chlorotic phenotype in true leaves with diminished chlorophyll a and b content, but unchanged Chl a/b ratio indicating a proportional decrease of both PSI and PSII complexes. Mitochondrial respiratory rates (state 3) were lower and the mitochondria were partially uncoupled. EM pictures on cross sections of the first true leaves showed aberrant chloroplasts, including less grana stacking and less starch granules. Mitochondria with extremely variable size could also be observed. At later developmental stages the plants appeared almost normal. However, all through the development there was a statistically significant decrease of approximately 40% in the accumulated biomass in the double mutant plants in comparison to wild type. In mitochondria, deletion of AtPreP was not compensated by activation of any peptidolytic activity, whereas chloroplast membranes contained a minor peptidolytic activity not related to AtPreP. In summary, the AtPreP peptidasome is required for efficient plant growth and organelle function particularly during early development.
一种新型肽体PreP负责线粒体和叶绿体中靶向肽及其他无结构肽的降解。拟南芥含有两种PreP亚型，即AtPreP1和AtPreP2。在此，我们对单个和双个prep基因敲除突变体进行了表征。对atprep1和atprep2突变体的免疫印迹分析表明，这两种亚型在所有组织中均有表达，在花和角果中的表达量最高；此外，与AtPreP2相比，AtPreP1积累到更高水平。atprep2突变体表现得与野生型相似，而AtPreP1的缺失导致幼苗略显淡绿色。对atprep1 atprep2双突变体的分析显示，真叶出现黄化表型，叶绿素a和b含量降低，但Chl a/b比值不变，表明PSI和PSII复合物均成比例减少。线粒体呼吸速率（状态3）较低，线粒体部分解偶联。第一片真叶横切面的电子显微镜照片显示叶绿体异常，包括基粒堆叠减少和淀粉粒减少。还可观察到大小极不相同的线粒体。在发育后期，植株看起来几乎正常。然而，在整个发育过程中，与野生型相比，双突变体植株的累积生物量在统计学上显著下降了约40%。在线粒体中，AtPreP的缺失未被任何肽水解活性的激活所补偿，而叶绿体膜含有一种与AtPreP无关的次要肽水解活性。总之，AtPreP肽体是植物高效生长和细胞器功能所必需的，尤其是在早期发育过程中。
