The extensive processing and protein-assisted stabilization of transcripts have been taken as evidence for a viewpoint that the control of gene expression had shifted entirely in evolution from transcriptional in the bacterial endosymbiont to posttranscriptional in the plastid. This suggestion is however at odds with many observations on plastid gene transcription. Chloroplasts of flowering plants and mosses contain two or more RNA polymerases with distinct promoter preference and division of labor for the coordinated synthesis of plastid RNAs. Plant and algal plastids further possess multiple nonredundant sigma factors that function as transcription initiation factors. The controlled accumulation of plastid sigma factors and modification of their activity by sigma-binding proteins and phosphorylation constitute additional transcriptional regulatory strategies. Plant and algal plastids also contain dedicated one- or two-component transcriptional regulators. Transcription initiation thus continues to form a critical control point at which varied developmental and environmental signals intersect with plastid gene expression.

转录物的广泛加工和蛋白质辅助稳定已被用作证据，证明了基因表达的控制已完全从细菌内共生体中的转录转变为质体中的后转录。然而，该建议与质体基因转录的许多观察结果不一致。开花植物和苔藓的叶绿体包含两种或多种具有聚合酶链反应的启动子偏好和分工的RNA聚合酶，可协调合成质体RNA。植物和藻类质体还具有多个非冗余的sigma因子，可作为转录起始因子。质体sigma因子的受控积累以及通过sigma结合蛋白和磷酸化修饰其活性构成了其他转录调控策略。植物和藻类质体还包含专用的一或二组分转录调节因子。因此，转录起始继续形成关键的控制点，在该控制点上，各种发育和环境信号与质体基因表达相交。