To engineer the pathway toward -carotene formation, it is
necessary to complement four plant enzymes, namely phytoene
synthase, phytoene desaturase, -carotene desaturase
(the desaturases catalyzing the introduction of two double
bonds, each), and lycopene -cyclase. Alternatively, the transformation
effort can be simplified by reducing the number of
enzymes required and using a bacterial carotene desaturases
capable of introducing all four double bonds required