Abstract
Chlorophyllide a oxygenase (CAO) is a rieske-type monooxygenase that catalyzes the conversion of chlorophyll a to chlorophyll b. CAO protein consists of three domains, namely, A, B and C domains. The A domain alone is involved in the regulatory mechanism of the CAO protein level. Previously, we reported that both accumulation of chlorophyll b and presence of Clp protease are necessary for the activity of CAO degradation. In this study, we demonstrated that a sequence of 10 amino acid residues which locates in the middle of the A domain is essential for the regulation of the CAO protein level. Furthermore, addition of this sequence to GFP significantly reduced the accumulation of GFP in transgenic plants, indicating that this sequence may is a tag to induce degradation of chloroplast proteins. Possible degradation mechanisms that involve the recognition of the sequence tag by Clp protease will be discussed.
