PARENT SESSION
Posters P7B Evolution of photosynthesis. Abstracts (579-591)

Transcriptional regulation of plastid-encoded genes in the unicellular red algae, Cyanidioschyzon merolae. Ayumi Minoda^*,1, Kan Tanaka¹, ¹ Institute of Molecular and Cellular Biosciences, Tokyo, Japan

ABSTRACT- Photosynthesis is never achieved without the strict regulatory mechanisms responding to the extensive environmental changes, and transcription is one of the important regulatory steps for the acclimation in photosynthetic organisms. Plastids, photosynthetic organella originated from endosymbiosis of a cyanobacteria-like prokaryote retain their own genome including many photosynthetic genes. In the plastid genome of higher plants, regulatory factors governing their own gene expression have been lost and appear to be substituted by many nuclear-encoded regulatory factors. In contract, four transcription factors (Ycf27-30) are retained in the plastid genome of a primitive red alga, Cyanidioschyzon merolae. Moreover, recent determination of the nuclear sequence of C. merolae revealed several nuclear-encoded regulatory factors concerned with the plastid gene expression, i.e., four sigma factors (SIG1-4) and a histidine kinase (HIK). In order to clarify the regulation of photosynthetic genes, the mechanism of the plastid gene expression in C. merolae must be so simple that it is our favored model system. The regulation model is also interesting in view of the evolution of the plastids. Ycf27 and Ycf29 are response regulators, which may comprise two-component system with HIK. Ycf28 and Ycf30 are homologs of transcription factors in cyanobacteria, NtcA known as a global nitrogen regulator and RbcR suggested as an activator of Rubisco genes, respectively. We made the His-tag or MBP-tag fused Ycf27-30 proteins with the over-expression system in E. coli. First, we will discuss the role of Ycf30 in the regulatory model of the Rubisco genes. Second, we found the transient increase in mRNA of the ycf27, HIK and SIG2 genes after shift to the high light condition. We will also discuss that the regulatory model of plastid gene expression and the role of Ycf27 under high light conditions. Third, we will present evidence suggesting the regulatory target genes of Yc29.

KEY WORDS: evolution, plastid , Cyanidioschyzon merolae, transcriptional regulation