Poster: Transcription Regulation

Abs # 1068: The cfxQ gene is encoded both in the plastid genome and in the cell nucleus of Cyanidioschyzon merolae

Presenter:	Ohta, Niji , niji@molbiol.saitama-u.ac.jp
Authors	Ohta, Niji  (A)   Fujita, Kiyohito  (A)   Kuroiwa, Tsuneyoshi  (B)
Affiliations:	(A): Department of Molecular biology, Faculty of Science, Saitama University (B): Department of Biology, Rikkyo University

The plant uses RuBisCO for carbon fixation. Chlorophytes and graucophytes have RuBisCO originated from the ancestral cyanobacterium. The RuBisCO operon of cyanobacteria is constituted of rbcL-rbcS. Graucophytes contain rbcL-rbcS in their plastid genomes, and Chlorophytes contains rbcL in the plastid genome and rbcS in the cell nucleus. Rhodophytes and chromophytes contain RuBisco originated from the ancestral beta-proteobacterium. The RuBisCO genes of rhodophytes and chromophytes are thought to the result of horizontal transfer from a beta-proteobacterium. The RuBisCO operon of beta-proteobacteria is rbcL-rbcS-cfxQ. Therefore, the RuBisCO operon of rhodophytes and chromophytes is rbcL-rbcS-cfxQ in the plastid genome of those organisms investigated so far. In Rhodophytes and chromophytes, RuBisCO operon is encoded in the plastid genome. We investigated in the RuBisCO operon of Cyanidioschyzon merolae. Complete nucleotide sequence of the plastid genome of C. merolae which is thought to be one of the most primitive algae shows that RuBisCO operon is encodedin the plastid genome. The cDNA analysis and complete genome sequence analysis, which is almost complete, show that cfxQ is also encoded in the cell nucleus. In cryptophytes, Guilardia theta contains cfxQ both in the plastid and in the nucleomorph. The phylogenetic analysis of cfxQ genes shows that the cfxQs in the plastid genomes make one group, and the cfxQs in the cell nucleus and nucleomorph makes another group. The results show that cfxQ is separately transferred to the cell nucleus and the plastid in the course of horizontal transfer of the RuBisCO operon from an ancestral beta-proteobacterium and an ancestral rhodophyte.