Plastid Transcription: A Major Regulatory Point in Chloroplast Biogenesis

Plastids are endosymbionts that retain their own, minimal genome that must be transcribed. This genome is known as the plastome. The host cell nucleus exerts tight control over the plastome to ensure the accurate timing of key developmental events, such as chloroplast biogenesis. Therefore, communication from the nucleus to the plastid, or anterograde signaling, is a vital step in plastome expression. Regulation of plastid transcription by the nucleus is tied to two DNA-dependent RNA polymerases that transcribe the plastome: the nuclear-encoded polymerase (NEP) and the plastid-encoded polymerase (PEP), which contains numerous nuclear-encoded PEP-associated proteins (PAPs). This chapter will cover the fundamentals and regulation of plastome transcription, with a focus on the role of plastid transcription in chloroplast biogenesis. In particular, the chapter will highlight the regulatory strategy of the nucleus to comprehensively control plastome gene expression through the assembly and activation of the PEP supercomplex, which is coordinated by both environmental and developmental factors.