CHARACTERIZATION OF A PLASTID SIGMA FACTOR AtSIGS RESPONSIBLE FOR JHE psbD LIGHT-RESPONSIVE TRANSCRIPTION

摘要

Plastid transcription is mediated by two types of RNA polymerase (RNAP), eubacterial-type PEP and T7 phage-type NEP. PEP is known to exclusively transcribe photosynthesis genes and indispensable for chloroplast development. The core catalytic enzyme of PEP is encoded by four plastid genes, whereas exchangeable promoter specifying sigma factors are encoded in nuclear genome. In analogy with bacterial RNAP, the replacement of sigma factors associated with PEP core has been assumed to be a major mechanism for the switching of transcription patterns in response to environmental and developmental signals. Six sigma factor genes have been identified in Arabidopsis thaliana. Recent molecular analyses of plant sigma factors revealed that Arabidopsis sigma factors are classified into general sigma factors responsible for the global transcription in chloroplasts (e.g. AtSIG6) and specialized sigma factors involved in transcription initiation at a few unusual promoters in response to environmental signals.