Bock R, Kössel H, Maliga P
Waksman Institute, Rutgers, State University of New Jersey, Piscataway 08855-0759.
EMBO J. 1994 Oct 3;13(19):4623-8. doi: 10.1002/j.1460-2075.1994.tb06784.x.
The psbF mRNA is edited in spinach plastids by a C to U conversion, changing a serine to a conserved phenylalanine codon. In tobacco at this position a phenylalanine codon is present at the DNA level, and the psbF mRNA here is not edited. To test if the psbF editing capacity is evolutionarily conserved, the tobacco psbF gene was modified to match the corresponding spinach sequence. The endogenous tobacco gene was replaced with the modified copy using biolistic transformation. We report here that the heterologous editing site remains unmodified in transplastomic tobacco plants. The lack of editing is associated with slower growth, lowered chlorophyll content and high chlorophyll fluorescence, a phenotype characteristic of photosynthetic mutants. This finding confirms that the editing of the psbF mRNA is an essential processing step for protein function and thus provides direct proof for the biological significance of plant organellar RNA editing. Given that a mutant phenotype is associated with the lack of editing, it seems likely that the evolutionary loss of the site-specific capacity for psbF editing was preceded by the mutation that eliminated the editing requirement.
菠菜质体中的psbF信使核糖核酸（mRNA）通过胞嘧啶（C）到尿嘧啶（U）的转变进行编辑，将一个丝氨酸密码子转变为一个保守的苯丙氨酸密码子。在烟草中，该位置在DNA水平上就存在苯丙氨酸密码子，因此这里的psbF mRNA未被编辑。为了测试psbF的编辑能力在进化上是否保守，对烟草psbF基因进行了修改，使其与菠菜的相应序列匹配。通过基因枪转化，用修改后的拷贝替换了烟草的内源基因。我们在此报告，在转质体烟草植株中，异源编辑位点未被修改。缺乏编辑与生长缓慢、叶绿素含量降低和叶绿素荧光增强有关，这是光合突变体的典型表型。这一发现证实了psbF mRNA的编辑是蛋白质功能的一个重要加工步骤，从而为植物细胞器RNA编辑的生物学意义提供了直接证据。鉴于突变表型与缺乏编辑有关，似乎在消除编辑需求的突变之前，psbF编辑的位点特异性能力在进化过程中就已经丧失。
