Characterization of two genes, Sig1 and Sig2, encoding distinct plastid σ factors1 in the moss Physcomitrella patens: phylogenetic relationships to plastid σ factors in higher plants

摘要

>We isolated the cDNA for a σ factor from the moss Physcomitrella patens, which possesses unusually large N-terminal extension and the conserved subdomains 1.2–4.2. Phylogenetic analyses indicated that this novel σ factor and PpSIG1* 2, a plastid σ factor previously identified from Physcomitrella, were classified into SigA and SigB groups, two major classes of higher plant plastid σ factors, respectively. According to the nomenclature recently proposed, we renamed PpSIG1* into PpSIG2, and named the novel σ factor PpSIG1. A transient expression assay using a green fluorescent protein showed that the N-terminal region of PpSIG1 acts as a chloroplast-targeting signal. Reverse transcription-PCR experiments showed that light induces the expression of the Sig1 and Sig2 genes encoding PpSIG1 and PpSIG2, respectively. Thus, PpSIG1 and PpSIG2 are likely plastid σ factors regulating plastid gene expression in response to light signals.