<p>This entry represents certain plastid RNA polymerase sigma factors, including SigB, SigC and SigD [<cite idref="PUB00042712"/>, <cite idref="PUB00042713"/>]. Development of plastids into chloroplasts is triggered by light. The coordination of light-induced plastid gene expression is directed by both nuclear and plastid genomes. Plastid DNA is transcribed by at least two types of RNA polymerase, plastid-encoded RNA polymerase (PEP) and nuclear-encoded RNA polymerase (NEP). Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released. Sigma factor SigB appears to play a critical role in the coordination of the two genomes for chloroplast development [<cite idref="PUB00042714"/>].</p> RNA polymerase sigma factor, SigB/SigC/SigD, plastid