Chlorophyll degradation is a key feature of different developmental processes ofplants such as fruit ripening and leaf senescence. The end products ofdegradation are colorless linear tetrapyrroles that are stored in the vacuoles ofsenescing cells. These products, termed “phyllobilins”, are derived fromchlorophyll by a multi-step pathway that involves an oxygenolytic opening of theporphyrin ring by PAO as the key step.Comparison of the chemical structures of phyllobilins from different plantspecies uncovered that modification at different side positions of the commontetrapyrrolic backbone occur in a species-specific manner. In Arabidopsisthaliana, at least four reactions are involved in the formation of more than tenstructurally different phyllobilins.We aimed at identifying the enzymes that catalyze these phyllobilinmodifications. Genes of two of the involved enzymes, i.e. a methylesterase anda cytochrome P450 monooxygenase, could be identified because of their closeco-expression with other known chlorophyll catabolic genes. Ethyl side chainhydroxylation is catalyzed by a Rieske-type monooxygenase, which is highlyhomologous to PAO. Different subcellular compartments are involved inphyllobilin modification as concluded from the localization and substratespecificity of the three proteins.

第129回 Plant Science Seminar

Chlorophyll breakdown during senescence: complexity of

chlorophyll catabolite modification

日時 ： １１月２日(月) １６：００〜１７：００場所 ： 理学部 ５号館 ８階 ８１３号室

Stefan Hörtensteiner 博士Institute of Plant Biology, University of Zurich, Switzerland

Plant Science SeminarStefan Hörtensteiner教授は植物の老化やクロロフィル分解に関して多くの先駆

的な研究をされ、長くに渡りこの分野を牽引されてきました。北大を訪問される機会に、クロロフィル分解に関してお話をして頂くことになりました。

Ref.1. Chlorophyll degradation during senescence. Annu. Rev. Plant Biol. (2006)2. Cytochrome P450 CYP89A9 is involved in the formation of major chlorophyll catabolites

during leaf senescence in Arabidopsis. Plant Cell (2013)3. Different Mechanisms are responsible for chlorophyll dephytylation during fruit ripening and

leaf senescence in tomato. Plant Physiology (2014)

世話人：田中歩（ayumi@pop.lowtem.hokudai.ac.jp）