Department of Plant Biology, 612 Wilson Road, Room 339, Michigan State University, East Lansing, MI 48824, USA.
Plant J. 2012 Dec;72(5):856-67. doi: 10.1111/tpj.12001. Epub 2012 Oct 12.
The Arabidopsis arc1 (accumulation and replication of chloroplasts 1) mutant has pale seedlings and smaller, more numerous chloroplasts than the wild type. Previous work has suggested that arc1 affects the timing of chloroplast division but does not function directly in the division process. We isolated ARC1 by map-based cloning and discovered it encodes FtsHi1 (At4g23940), one of several FtsHi proteins in Arabidopsis. These poorly studied proteins resemble FtsH metalloproteases important for organelle biogenesis and protein quality control but are presumed to be proteolytically inactive. FtsHi1 bears a predicted chloroplast transit peptide and localizes to the chloroplast envelope membrane. Phenotypic studies showed that arc1 (hereafter ftsHi1-1), which bears a missense mutation, is a weak allele of FtsHi1 that disrupts thylakoid development and reduces de-etiolation efficiency in seedlings, suggesting that FtsHi1 is important for chloroplast biogenesis. Consistent with this finding, transgenic plants suppressed for accumulation of an FtsHi1 fusion protein were often variegated. A strong T-DNA insertion allele, ftsHi1-2, caused embryo-lethality, indicating that FtsHi1 is an essential gene product. A wild-type FtsHi1 transgene rescued both the chloroplast division and pale phenotypes of ftsHi1-1 and the embryo-lethal phenotype of ftsHi1-2. FtsHi1 overexpression produced a subtle increase in chloroplast size and decrease in chloroplast number in wild-type plants while suppression led to increased numbers of small chloroplasts, providing new evidence that FtsHi1 negatively influences chloroplast division. Taken together, our analyses reveal that FtsHi1 functions in an essential, envelope-associated process that may couple plastid development with division.
拟南芥 arc1（叶绿体积累和复制 1）突变体的幼苗呈苍白色，叶绿体比野生型更小、更多。先前的工作表明，arc1 影响叶绿体分裂的时间，但不直接作用于分裂过程。我们通过图谱克隆分离了 ARC1，并发现它编码 FtsHi1（At4g23940），这是拟南芥中几种 FtsHi 蛋白之一。这些研究较少的蛋白类似于对细胞器生物发生和蛋白质质量控制很重要的 FtsH 金属蛋白酶，但据推测它们没有蛋白水解活性。FtsHi1 具有预测的叶绿体转运肽，并定位在叶绿体被膜上。表型研究表明，携带错义突变的 arc1（以下简称 ftsHi1-1）是 FtsHi1 的弱等位基因，破坏类囊体发育并降低幼苗去黄化效率，表明 FtsHi1 对叶绿体生物发生很重要。与这一发现一致的是，积累 FtsHi1 融合蛋白的转基因植物常常出现斑驳现象。一个强的 T-DNA 插入等位基因 ftsHi1-2 导致胚胎致死，表明 FtsHi1 是一个必需的基因产物。一个野生型 FtsHi1 转基因拯救了 ftsHi1-1 的叶绿体分裂和苍白色表型以及 ftsHi1-2 的胚胎致死表型。FtsHi1 过表达在野生型植物中导致叶绿体大小略有增加和叶绿体数量减少，而抑制导致小叶绿体数量增加，这为 FtsHi1 负调控叶绿体分裂提供了新证据。总之，我们的分析表明，FtsHi1 在一个必需的、与被膜相关的过程中发挥作用，该过程可能将质体发育与分裂偶联起来。
