Abstract
In higher plants, sigma factors of PEP (plastid-encoded RNA polymerase) are encoded by nuclear genes, and regulate plastid developments and proliferation. In A.thaliana, six sigma factors were identified and their functions were analyzed. Among them, SIG5 shows responsive to blue light and stress signals such as high-salt and high-light. Previously, we identified two isoforms of SIG5 homologues in soybean (GmSIG5A, 5B) and demonstrated the responsiveness of GmSIG5B to stress signals. Here, we focus on SIG5 homologues for their phylogenetics and functional specificity, and surveyed SIG5 homologue genes in other plant species. Firstly, PCR using degenerate primers resulted in successful amplification of portions of possible SIG5-homologue genes from tomato, clover and cherry tree. Further survey of databases based on the possible SIG5-signature sequence revealed the existence of SIG5 homologue genes in many plants species involving poplar and spruce. To further examine the phylogenetical significance of SIG5, we also searched SIG5 homologue genes in some gymnosperms. Results obtained indicate that SIG5 homologues prevail among land plants as a stress-responsive sigma factor.
