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.
^Breitenbach J, Zhu C, Sandmann G (November 2001). "Bleaching herbicide norflurazon inhibits phytoene desaturase by competition with the cofactors". Journal of Agricultural and Food Chemistry. 49 (11): 5270–2. doi:10.1021/jf0106751. PMID11714315.
^Sandmann, Gerhard (2002). "2: Bleaching Herbicides: Action Mechanism in Carotenoid Biosynthesis, Structural Requirements and Engineering of Resistance". In Böger, Peter; Wakabayashi, Ko; Hirai, Kenji (eds.). Herbicide Classes in Development: Mode of Action, Targets, Genetic Engineering, Chemistry (1 ed.). Springer-Verlag Berlin Heidelberg. pp. 43–57. doi:10.1007/978-3-642-59416-8_2. ISBN978-3-642-63972-2.