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Chlorophyll b is an ubiquitous accessory pigment in land plants, green algae, and prochlorophytes. Its biosynthesis plays a key role in the adaptation to various light environments. We isolated six chlorophyll b-less mutants by insertional mutagenesis by using the nitrate reductase or argininosuccinate lyase genes as tags and examined the rearrangement of mutant genomes. We found that an overlapping region of a nuclear genome was deleted in all mutants and that this encodes a protein whose sequence is similar to those of methyl monooxygenases. This coding sequence also contains putative binding domains for a 2Fe-2S Rieske center and for a mononuclear iron. The results demonstrate that a chlorophyll a oxygenase is involved in chlorophyll b formation. The reaction mechanism of chlorophyll b formation is discussed.
Tanaka et al. (Tue,) studied this question.