Abstract
Plastids contain multiple copies of circular DNA encoding about 40 photosynthesis and 60 housekeeping genes. These genes are transcribed by two types of RNA polymerase, eubacterial-type PEP and phage-type NEP. Photosynthesis genes are mainly transcribed by PEP (class I genes), whereas both PEP and NEP are involved in transcription of other housekeeping genes (class II gene). Some exceptional genes (rpoA and rpoB operon genes and accD) are exclusively transcribed by NEP (class III gene). To gain further molecular insight into developmental and tissue-specific characteristics of plastids, we analyzed the expression profiles of plastid genes at different developmental stages and in various tissues. Class I and some class II genes are actively transcribed in chloroplasts, while different sets of genes are transcribed in non-photosynthetic plastids in roots and siliques. Furthermore, we found that plastid gene expression is dynamically regulated during seedling development and seed maturation.
