These authors contributed equally.
Light induction of Arabidopsis SIG1 and SIG5 transcripts in mature leaves: differential roles of cryptochrome 1 and cryptochrome 2 and dual function of SIG5 in the recognition of plastid promoters
Article first published online: 4 JUN 2008
© 2008 The Authors. Journal compilation © 2008 Blackwell Publishing Ltd
The Plant Journal
Volume 55, Issue 6, pages 968–978, September 2008
How to Cite
Onda, Y., Yagi, Y., Saito, Y., Takenaka, N. and Toyoshima, Y. (2008), Light induction of Arabidopsis SIG1 and SIG5 transcripts in mature leaves: differential roles of cryptochrome 1 and cryptochrome 2 and dual function of SIG5 in the recognition of plastid promoters. The Plant Journal, 55: 968–978. doi: 10.1111/j.1365-313X.2008.03567.x
- Issue published online: 4 SEP 2008
- Article first published online: 4 JUN 2008
- Received 9 December 2007; revised 20 March 2008; accepted 8 May 2008; published online 11 July 2008.
- plastid sigma factor;
- plastid-encoded RNA polymerase-dependent promoter;
In higher plants, multiple nuclear-encoded sigma factors activate select subsets of plastid gene promoters in a partially redundant manner. We analysed the light induction profiles of transcripts from six Arabidopsis sigma factor (AtSIG) genes in mature leaves, focusing on the effects of wavelength and intensity. Red-light illumination (660 nm) of dark-adapted plants strongly induced AtSIG1 transcripts, while blue-light illumination (470 nm) caused strong and rapid induction of AtSIG1 and AtSIG5 transcripts. The fluence response differed in blue-light-responsive rapid induction in AtSIG1 and AtSIG5. AtSIG1 transcripts increased to plateau with a threshold of 2 μmol m−2 sec−1 under all fluences examined (1–50 μmol m−2 sec−1), and AtSIG5 transcripts were induced with a distinct two-phase profile, with the lower-fluence induction similar to that of AtSIG1 and further enhancement with increasing fluences greater than 10 μmol m−2 sec−1. Blue-light-receptor mutational analysis revealed that AtSIG5-specific two-phase induction is mediated through cryptochrome 1 and cryptochrome 2 at lower fluences and more significantly through cryptochrome 1 at higher fluences. In mature chloroplasts, the promoters of psbA and psbD are predominantly recognized by AtSIG5 among six sigma factors. Using a protoplast transient expression assay with AtSIG5–AtSIG1 chimeric genes, we present evidence that AtSIG5 contains determinants for activating the psbD blue-light-responsive promoter (BLRP) in region 4.2 rather than region 2.4. Amino acid scanning within AtSIG5 region 4.2 revealed that Asn484, but not Arg493, functions as a key residue for psbD BLRP activation. Arginine 493 may be involved in psbA promoter recognition.