Abstract
Chlorophyllide a oxygenase (CAO) is a Rieske-type monooxygenase that catalyzes conversion of chlorophyll a to chlorophyll b. CAO consists of three domains that are named A, B, and C. We hypothesized that A domain regulates CAO protein levels, B domain is a linker and C domain has a catalytic function. In this study, we examined the localization of CAO in chloroplasts. We examined accumulation patterns of CAO-GFP fusions in transgenic plants that overexpressed various combination of CAO domains with GFP by confocal microscopy and immunogold labeling electron microscopy. We found that accumulation patterns were different depending on the presence of A domain or C domain. These results indicate that CAO is localized in a specific site in chloroplasts, and that C domain plays an essential role in this localization. We are also examining the degradation mechanism of CAO by analyzing mutants that have defects in the repression of CAO accumulation.
