Mechanism of the diletion of plastid DNA in pollen-derived albino and its application as a vector.

来自花粉的白化水稻植株含有大量缺失的质体基因组。从白化植物的根中，我们获得了几个含有均匀质体DNA的愈伤组织，其大小和缺失的位置不同。Southern印迹和脉冲场凝胶电泳实验表明，dna是线性分子，在两端具有发夹结构，以单体（19kb）或二聚体的形式存在，三聚体和四聚体喜欢形成头对头和尾对尾的多聚体。这种特征形式与牛痘病毒相似，在牛痘病毒中，复制起源被认为位于发夹末端或附近。此外，聚合酶链反应实验显示，质体DNA的核糖体RNA基因完全丢失。结果表明，植物细胞可以在没有质体翻译的情况下生长。所有缺失的质体dna通常保留含有tRNA^<Glu>基因（trnE）的区域，该区域对卟啉的生物合成至关重要。由于卟啉是线粒体和其他细胞器血红素的前体，因此认为残余质体基因组上的trnE可能是由核DNA编码的RNA聚合酶转录的。

Albino rice plants derived from pollen contain plastid genomes that have suffered large-scale deletions. From the roots of albino plants, we obtained several calli containing homogeneous plastid DNA differing in the size and position of the deletion. Southern blotting and pulsed field gel electrophoresis experiments revealed that the DNAs were linear molecules having a hairpin structure at both termini, existing as monomers (19 kb) or dimers, trimers and tetramers liked to form head-to-head and tail-to-tail multimers. This characteristic form is similar to that of the vaccinia virus, in which the replication origin is thought to lie at or near the hairpin termini. Farthermore, polymerase chain reaction experiments revealed complete loss of the ribosomal RNA genes of the plastid DNA. The results suggest that plant cells can grow without translation occurring in plastids. All of the deleted plastid DNAs commonly retained the region containing the tRNA^<Glu> gene(trnE), which is essential for biosynthesis of porphyrin. As porphyrin is the precursor of heme for mitochondria and other organelles, it is considered that trnE on the remnant plastid genome may be transcribed by an RNA polymerase encoded on nuclear DNA.