Chlorophyll <i>a</i> oxygenase ( <i>CAO</i> ) is involved in chlorophyll <i>b</i> formation from chlorophyll <i>a</i>

TLDR

Chlorophyll b, an ubiquitous accessory pigment in land plants, green algae, and prochlorophytes, is essential for adaptation to diverse light environments, and its biosynthetic mechanism has been a subject of study. The study aimed to isolate chlorophyll b‑less mutants and examine genome rearrangements. This was achieved by insertional mutagenesis using nitrate reductase or argininosuccinate lyase gene tags. All mutants shared a deletion of a nuclear region encoding a methyl monooxygenase‑like protein with putative [2Fe‑2S] Rieske and mononuclear iron binding domains, confirming that a chlorophyll a oxygenase mediates chlorophyll b formation.

Abstract

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.