Arabidopsis , Mendel's Green Cotyledon Gene, Encodes Magnesium-Dechelatase.

Pheophytin is an essential component of oxygenic photosynthetic organisms because the primary charge separation between chlorophyll and pheophytin is the first step in the conversion of light energy. In addition, conversion of chlorophyll to pheophytin is the first step of chlorophyll degradation. Pheophytin is synthesized by extracting magnesium (Mg) from chlorophyll; the enzyme Mg-dechelatase catalyzes this reaction. In this study, we report that Mendel's green cotyledon gene, (), encodes Mg-dechelatase. The genome has three genes, , , and (). Recombinant SGR1/2 extracted Mg from chlorophyll but had very low or no activity against chlorophyllide ; by contrast, SGRL had higher dechelating activity against chlorophyllide compared with chlorophyll All SGRs could not extract Mg from chlorophyll Enzymatic experiments using the photosystem and light-harvesting complexes showed that SGR extracts Mg not only from free chlorophyll but also from chlorophyll in the chlorophyll-protein complexes. Furthermore, most of the chlorophyll and chlorophyll binding proteins disappeared when SGR was transiently expressed by a chemical induction system. Thus, SGR is not only involved in chlorophyll degradation but also contributes to photosystem degradation.