**4. Potential mechanisms that regulate the synthesis of astaxanthin**

The astaxanthin synthesis pathway has been extensively studied, and most of genes and enzymes involved are currently known. More recent studies have focused on elucidating the possible regulation mechanisms of carotenogenesis. In the case of yeast *X. dendrorhous*, special emphasis has been placed on understanding the effect of the carbon source on carotenogenesis and how this pathway is affected by other related pathways, such as the synthesis of sterols. In the case of *H. pluvialis*, special interest has been placed on the effect of small molecules on the synthesis of astaxanthin.
