The conversion of phytoene to lycopene in plants and cyanobacteria (left) compared to bacteria and fungi(right).
PDS converts 15-cis-phytoene into 9,15,9'-tri-cis-ζ-carotene through reduction of the enzymes non-covalently bound
FAD cofactor.[6] This conversion introduces two additional double bonds at positions 11 and 11' of the carbon chain and isomerizes two adjacent already existing double bonds at positions 9 and 9' from
trans to cis. The electrons involved in the reaction are subsequently transferred onto
plastoquinone[7] and to
plastid terminal oxidase PTOX ultimately coupling the desaturation to oxygen reduction. Disruption of this biosynthesis step results in
albinism and stunted plant growth.[8]
Applications
Disruption of PDS function can be achieved by bleaching herbicides such as norflurazon[9] and
fluridone.[10] These inhibitors occupy the binding pocket of plastoquinone within the enzyme thus blocking it from its function.[1] Due to the clear effect of PDS disruption in plants, the corresponding gene was targeted to showcase successful genome editing in fruit such as apples,[11] grapes[12] or bananas[13] using
CRISPR/Cas9 systems. In
rice, the natural PDS was supplemented by its bacterial
homolog to create
Golden Rice and thus increase the
β-carotene content of the rice
endosperm.
^Schneider C, Böger P, Sandmann G (July 1997). "Phytoene desaturase: heterologous expression in an active state, purification, and biochemical properties". Protein Expression and Purification. 10 (2): 175–9.
doi:
10.1006/prep.1997.0730.
PMID9226712.
^Breitenbach J, Sandmann G (March 2005). "zeta-Carotene cis isomers as products and substrates in the plant poly-cis carotenoid biosynthetic pathway to lycopene". Planta. 220 (5): 785–93.
doi:
10.1007/s00425-004-1395-2.
PMID15503129.
S2CID23793453.