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.

Dynamics of light-induced conformational changes of the phoborhodopsin/transducer complex formed in the n-dodecyl beta-D-maltoside micelle.

A complex of photoreceptor phoborhodopsin (ppR; also called sensory rhodopsin II) and its cognate halobacterial transducer II (pHtrII) existing in the plasma membrane mediates the light signal to the cytoplasm in the earliest step of negative phototaxis in Natronomonas pharaonis. We have investigated the dynamics of the light-induced conformational changes of the ppR/pHtrII(1-159) complex formed in the presence of 0.1% n-dodecyl beta-d-maltoside (DDM) by a fluorescence resonance energy transfer (FRET) based method.

Application of fluorescence resonance energy transfer (FRET) to investigation of light-induced conformational changes of the phoborhodopsin/transducer complex.

The photoreceptor phoborhodopsin (ppR; also called sensory rhodopsin II) forms a complex with its cognate the Halobacterial transducer II (pHtrII) in the membrane, through which changes in the environmental light conditions are transmitted to the cytoplasm in Natronomonas pharaonis to evoke negative phototaxis. We have applied a fluorescence resonance energy transfer (FRET)-based method for investigation of the light-induced conformational changes of the ppR/pHtrII complex. Several far-red dyes were examined as possible fluorescence donors or acceptors because of the absence of the spectral overlap of these dyes with all the photointermediates of ppR.

Two independent light signals cooperate in the activation of the plastid psbD blue light-responsive promoter in Arabidopsis.

The psbD blue light-responsive promoter (BLRP), whose activation has been considered to require strong blue light, is recognized only by SIG5 among six sigma factors of plastid RNA polymerase in Arabidopsis. We found SIG5 transcript accumulation was rapidly induced after a 30-min induction time by blue light (470 nm) with an intensity threshold of 5 micromol m(-2)s(-1) through cryptochromes. Besides this weak blue light, the psbD BLRP activation required the stronger light such as 50 micromol m(-2)s(-1) irrespective of blue or red light (660 nm).

Blue light-induced transcription of plastid-encoded psbD gene is mediated by a nuclear-encoded transcription initiation factor, AtSig5.

Light is one of the most important environmental factors regulating expression of photosynthesis genes. The plastid psbD gene encoding the photosystem II reaction center protein D2 is under the control of a unique blue light responsive promoter (BLRP) that is transcribed by a bacterial-type plastid RNA polymerase (PEP). Promoter recognition of PEP is mediated by one of the six nuclear-encoded sigma factors in Arabidopsis.

A role of the -35 element in the initiation of transcription at psbA promoter in tobacco plastids.

Most plastid promoters recognized by bacteria-like plastid RNA polymerase (PEP) are similar to E. coli sigma(70)-type promoters comprising "-35" and "-10" elements. Among them, psbA promoter is unique in bearing additional elements between the conserved -35 and -10 elements.

Blue light specific and differential expression of a plastid sigma factor, Sig5 in Arabidopsis thaliana.

The transcription of plastid gene psbD is under the control of the BLRP (blue-light-responsive promoter) recognized by plastid-encoded RNA polymerase, in which nuclear-encoded sigma factors play a crucial role in the promoter recognition. We examined the effects of light on mRNA levels of six different SIG genes in Arabidopsis and found that blue light extensively induced the accumulation of SIG5 transcripts, but red light did not. The blue light specificity was not observed in the accumulations of remaining five SIG genes.

Novel nuclear-encoded proteins interacting with a plastid sigma factor, Sig1, in Arabidopsis thaliana.

Sigma factor binding proteins are involved in modifying the promoter preferences of the RNA polymerase in bacteria. We found the nuclear encoded protein (SibI) that is transported into chloroplasts and interacts specifically with the region 4 of Sig1 in Arabidopsis. SibI and its homologue, T3K9.