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.
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 micromol m(-2) sec(-1) under all fluences examined (1-50 micromol 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 micromol 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.
Department of Bioscience and Nano-biotechnology Research Centre, School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo, Japan.
Yayoi
Y
Onda
Yusuke
Y
Yagi
Yukiko
Y
Saito
Nobuhiro
N
Takenaka
Yoshinori
Y
Toyoshima
D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics*; D002478:Cells, Cultured; D056931:Cryptochromes; D004252:DNA Mutational Analysis; D005420:Flavoproteins / Q000235:genetics*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D008027:Light; D009154:Mutation; D045332:Photosystem II Protein Complex / Q000235:genetics; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D018087:Plastids / Q000235:genetics*; D011401:Promoter Regions, Genetic; D011523:Protoplasts / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics; D012808:Sigma Factor / Q000235:genetics*; D014158:Transcription, Genetic
D029681:Arabidopsis Proteins; C538962:CRY1 protein, Arabidopsis; D056931:Cryptochromes; D005420:Flavoproteins; D045332:Photosystem II Protein Complex; C479885:PsbD protein, Arabidopsis; D018749:RNA, Plant; C486979:Sig5 protein, Arabidopsis; C107904:SigA protein, Arabidopsis; D012808:Sigma Factor