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

• Published in: The Plant journal : for cell and molecular biology Vol. 55; no. 6; pp. 968 - 978
• Main Authors: Onda, Yayoi, Yagi, Yusuke, Saito, Yukiko, Takenaka, Nobuhiro, Toyoshima, Yoshinori
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.09.2008; Blackwell Publishing Ltd; Blackwell Science
• Subjects: Arabidopsis; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - genetics; Biological and medical sciences; Botany; Cells, Cultured; chloroplast; cryptochrome; Cryptochromes; DNA Mutational Analysis; Flavoproteins - genetics; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Plant; Genes, Plant; Genetics; Leaves; Light; Metabolism; Mutation; Photosystem II Protein Complex - genetics; Plant Leaves - genetics; Plant Leaves - metabolism; Plant physiology and development; plastid sigma factor; plastid-encoded RNA polymerase-dependent promoter; Plastids; Plastids - genetics; Promoter Regions, Genetic; Protoplasts - metabolism; RNA, Plant - genetics; Sigma Factor - genetics; Storage and secretion, pigments, phytochrome; transcription; Transcription, Genetic; Transcription; Enzyme; Arabidopsis; Transferases; plastid-encoded RNA polymerase- dependent promoter; Plant leaf; Plastid; DNA-directed RNA polymerase; Nucleotidyltransferases; Gene; Cruciferae; Dicotyledones; Aminoacid; Protoplast; Angiospermae; cryptochrome; Spermatophyta; Chloroplast; plastid sigma factor
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/j.1365-313x.2008.03567.x

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.