Asakura Yukari, Barkan Alice
Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403, USA.
Plant Physiol. 2006 Dec;142(4):1656-63. doi: 10.1104/pp.106.088096. Epub 2006 Oct 27.
Chloroplast genomes in plants and green algae contain numerous group II introns, large ribozymes that splice via the same chemical steps as spliceosome-mediated splicing in the nucleus. Most chloroplast group II introns are degenerate, requiring interaction with nucleus-encoded proteins to splice in vivo. Genetic approaches in maize (Zea mays) and Chlamydomonas reinhardtii have elucidated distinct sets of proteins that assemble with chloroplast group II introns and facilitate splicing. Little information is available, however, concerning these processes in Arabidopsis (Arabidopsis thaliana). To determine whether the paucity of data concerning chloroplast splicing factors in Arabidopsis reflects a fundamental difference between protein-facilitated group II splicing in monocot and dicot plants, we examined the mutant phenotypes associated with T-DNA insertions in Arabidopsis genes encoding orthologs of the maize chloroplast splicing factors CRS1, CAF1, and CAF2 (AtCRS1, AtCAF1, and AtCAF2). We show that the splicing functions and intron specificities of these proteins are largely conserved between maize and Arabidopsis, indicating that these proteins were recruited to promote the splicing of plastid group II introns prior to the divergence of monocot and dicot plants. We show further that AtCAF1 promotes the splicing of two group II introns, rpoC1 and clpP-intron 1, that are found in Arabidopsis but not in maize; AtCAF1 is the first splicing factor described for these introns. Finally, we show that a strong AtCAF2 allele conditions an embryo-lethal phenotype, adding to the body of data suggesting that cell viability is more sensitive to the loss of plastid translation in Arabidopsis than in maize.
植物和绿藻中的叶绿体基因组包含众多II类内含子，这些大型核酶通过与细胞核中剪接体介导的剪接相同的化学步骤进行剪接。大多数叶绿体II类内含子已退化，需要与细胞核编码的蛋白质相互作用才能在体内进行剪接。玉米（Zea mays）和莱茵衣藻（Chlamydomonas reinhardtii）中的遗传学方法已经阐明了与叶绿体II类内含子组装并促进剪接的不同蛋白质组。然而，关于拟南芥（Arabidopsis thaliana）中这些过程的信息却很少。为了确定拟南芥中叶绿体剪接因子数据的匮乏是否反映了单子叶植物和双子叶植物中蛋白质促进的II类剪接之间的根本差异，我们研究了与拟南芥中编码玉米叶绿体剪接因子CRS1、CAF1和CAF2（AtCRS1、AtCAF1和AtCAF2）直系同源基因的T-DNA插入相关的突变体表型。我们表明，这些蛋白质的剪接功能和内含子特异性在玉米和拟南芥之间基本保守，这表明在单子叶植物和双子叶植物分化之前，这些蛋白质就被招募来促进质体II类内含子的剪接。我们进一步表明，AtCAF1促进了拟南芥中存在但玉米中不存在的两个II类内含子rpoC1和clpP-内含子1的剪接；AtCAF1是针对这些内含子描述的第一个剪接因子。最后，我们表明一个强AtCAF2等位基因导致胚胎致死表型，这增加了数据表明细胞活力对拟南芥中质体翻译丧失比玉米更敏感。
