Colombo Noemí, Emanuel Carola, Lainez Verónica, Maldonado Sara, Prina Alberto R, Börner Thomas
Instituto de Genética Ewald A. Favret, CICVyA, CNIA, INTA, CC 25, B1712WAA Castelar, Buenos Aires, Argentina.
Mol Genet Genomics. 2008 Apr;279(4):403-14. doi: 10.1007/s00438-008-0321-x. Epub 2008 Mar 4.
The barley plastome mutant CL2 (cytoplasmic line 2) carries a point mutation in the infA gene, a homologue of the bacterial gene for the conserved translation initiator factor 1 (IF1). The function of infA in plastids is not known. The mutation in CL2 leads to a temporal chlorophyll deficiency in the primary leaf blade that is normalised in the basal and middle parts during further development. We have compared the expression of selected nuclear and plastid genes in different parts of primary leaves of CL2 and wild-type and found no indication for an adverse effect of the mutation on plastidial transcription. We observed an enhanced expression of RpoTp (encoding the phage-type nuclear-encoded plastid RNA polymerase) suggested to be caused by retrograde plastid signalling. Decreased amounts of plastid rRNA in basal and top sections are in agreement with the idea that the mutation in infA leads to a time- and position-dependent defect of plastid translation that causes a delay in plastid development. The normalisation of the phenotype in the middle section of CL2 leaves correlates with wild-type levels of chloroplast 16S rRNA and RbcL and increased expression of plastid housekeeping genes. The normalisation was not observed in cells at the tip of CL2 leaves suggesting different ways of regulating chloroplast development in cells at the tip of primary barley leaves as compared with other leaf sections.
大麦质体基因组突变体CL2（细胞质系2）在infA基因中存在一个点突变，该基因是细菌中保守翻译起始因子1（IF1）基因的同源物。infA在质体中的功能尚不清楚。CL2中的突变导致初生叶片暂时出现叶绿素缺乏，在进一步发育过程中，基部和中部的叶绿素缺乏现象会恢复正常。我们比较了CL2和野生型初生叶不同部位中选定的核基因和质体基因的表达，未发现该突变对质体转录有不利影响的迹象。我们观察到RpoTp（编码噬菌体类型的核编码质体RNA聚合酶）的表达增强，这表明是由质体逆行信号传导引起的。基部和顶部切片中质体rRNA含量的降低与infA突变导致质体翻译出现时间和位置依赖性缺陷从而导致质体发育延迟的观点一致。CL2叶片中部的表型恢复正常与叶绿体16S rRNA和RbcL的野生型水平以及质体管家基因表达增加相关。在CL2叶片尖端的细胞中未观察到这种恢复正常的现象，这表明与其他叶片部分相比，大麦初生叶尖端细胞中叶绿体发育的调节方式不同。
