Light-Regulation of Zeaxanthin Epoxidase in View of the Central Role of Zeaxanthin for Photoprotection.

Plants are frequently exposed to fluctuating light conditions and, as a consequence, to variable photo-oxidative stress. Efficient and flexible photoprotection is therefore essential for the fitness of plants in the field. The xanthophyll zeaxanthin, which is formed in high light from violaxanthin in the xanthophyll cycle, contributes to photoprotection in the thylakoid membrane at different levels, including the dissipation of excess light energy. Permanent high levels of zeaxanthin are known to compromise photosynthetic efficiency. It is thus of high importance to keep the amount of zeaxanthin at an optimal level in response to the growth light conditions. The zeaxanthin epoxidase, which reconverts zeaxanthin to violaxanthin, has been shown to be central to balancing the zeaxanthin amount in the thylakoid membrane. This review summarizes the recent advances in the understanding of the light regulation of zeaxanthin epoxidase in the context of the function of zeaxanthin in plant photoprotection.