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

Abstract

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 nuclearencoded factors in Arabidopsis. The replacement of the plastid factor associated with PEP may be the major mechanism for switching of plastid transcription pattern in response to environmental and developmental signals. This study demonstrates that AtSig5 is a unique factor that is essential for psbD BLRP activity. A T-DNA insertional mutant with reduced AtSIG5 expression resulted in loss of primary transcripts from the psbD BLRP. Furthermore, transient overexpression of AtSig5 in dark-adapted protoplasts specifically elevated psbD and psbA transcription activities. On the other hand, overproduction of AtSig2 enhanced the transcription of psbA gene and trnE operon, but not psbD transcription. The AtSIG5 gene is phylogenetically distinct from other plastid factors, and its expression is induced exclusively by blue light. We propose that AtSig5 acts as a mediator of blue light signaling that specifically activates the psbD BLRP in response to blue light in Arabidopsis.

A comparative analysis of basic helix-loop-helix proteins, AtPTF1 and NtWIN4, with reference to plastid localization

“…been rather controversial as to its function and localization. For example, psbD LRP was shown to be transcribed by a nuclear-encoded transcription factor, AtSig5 (Tsunoyama et al 2004). This was confirmed with a mutant, sig5, in which psbD LRP activity was completely eliminated, whereas in ptf1 mutants the activity was not affected (Baba et al 2001).…”

“…This was confirmed with a mutant, sig5, in which psbD LRP activity was completely eliminated, whereas in ptf1 mutants the activity was not affected (Baba et al 2001). AtPTF1 is unlikely to be involved in light signaling based on the finding that light-dependent psbD transcription was not diminished in AtPTF1-deficient mutants (Tsunoyama et al 2004). Overall, above-mentioned genetic and our present biochemical studies pointed to that AtPTF1 might be a nuclear transcriptional repressor.…”

“…Due to its unique features, AtPTF1 has often been referred to as an example of non-nuclear localized bHLH protein (Nagashima et al 2004;Tsunoyama et al 2004;Hanaoka et al 2003;Sekine et al 2002;Thum et al 2001;Kanamaru et al 2001 Table 1. Prediction of plastid localization within NtWIN4 and AtPTF1.…”

Mitochondrial Protein Lipoylation Does Not Exclusively Depend on the mtKAS Pathway of de Novo Fatty Acid Synthesis in Arabidopsis

“…3), represent knockout alleles for the gene mtKAS. The use of two additional primer combinations for reverse transcriptase (RT)-mediated PCR, covering transcript ranges upstream of the last exon, revealed the presence of aberrant transcripts (data not shown), which is frequently observed with T-DNA insertions in the last exon (for example, Tsunoyama et al, 2004).…”

COP1-Mediated Degradation of BBX22/LZF1 Optimizes Seedling Development in Arabidopsis

“…observation that BBX22 regulates chloroplast development (Chang et al, 2008), genes regulated by BBX22 include ELIP1, ELIP2, CRY3/CRYD, and SIG5/SIGE, which encode chloroplast proteins (Yao et al, 2003;Tsunoyama et al, 2004;Heddad et al, 2006;Pokorny et al, 2008). ELIP1 and ELIP2, transiently induced by different qualities of light, encode thylakoid proteins functioning in chlorophyll biosynthesis (Casazza et al, 2005;Rossini et al, 2006).…”