Poster: Organelle Biogenesis

Abs # 1158: Transcription regulation of the Rubisco operon in Cyanidioshcyzon merolae

Presenter:	Minoda, Ayumi , aa17115@mail.ecc.u-tokyo.ac.jp
Authors	Minoda, Ayumi  (A)   Tanaka, Kan  (A)   Takahashi, Hideo  (A)
Affiliations:	(A): Institute of Molecular and cellular biosciences, the University of Tokyo

Responding to environmental changes, transcription regulation is a major strategy in free-living organisms. And as an organelle, plastids lost most of transcription regulatory factors during the evolution after the cyanobacterial endosymbiosis. Especially in green plant plastids, almost all of the cyanobacteria-derived transcription regulators have been lost, and only sigma factors have been conserved in the nuclear genome to control the plastid gene expression. In contrast to green plants, plastid genomes of non-green plant lineages encode several bacteria-type transcription factors, indicating the presence of plastid-autonomous transcription regulation. Cyanidioschyzon merolae is a unicellular and primitive red alga, and is our favorite model system. Four putative transcription factors (Ycf27-30) are encoded by the plastid genome, and the clarification of their roles is the purpose of our present research. Ycf30 is a homologue of CbbR of photosynthetic bacteria, where the transcription of the Rubisco operon is under the CbbR control. In C. merolae, expression of the plastid-encoded rbcL, rbcS and cfxQ genes was found to be activated during the low CO₂ acclimation using DNA microarray analyses. Northern hybridization analyses have also revealed that these three genes were transcribed as an operon in this order. The transcription activation by the CO₂ downshift was suppressed by the addition of chloramphenicol but not by cycloheximide, indicating that the plastid encoded gene expression is essential for the rbcL promoter activation. Thus, we postulate that the plastid encoded ycf30 gene product is involved in this transcription regulation. In the meeting, we will also report the promoter structure of the rbc-operon and propose a regulatory model.