Cloning, sequencing and functional assignment of the chlorophyll biosynthesis gene, chlP, of Synechocystis sp. PCC 6803

Abstract

A gene from the cyanobacterium Synechocystis sp. PCC 6803 has been cloned and sequenced, and subsequently used to partially complement a bchP mutant of the purple photosynthetic bacterium Rhodobacter sphaeroides. This mutant is blocked in the terminal hydrogenation steps of bchl a biosynthesis and possesses only bchl esterified with geranylgeraniol. It also has a reduced cellular level of the light-harvesting LH2 complex, and the 850 nm absorbance maximum of LH2 is red-shifted by approximately 6 nm. Upon heterologous expression of the Synechocystis bchP homologue, not only are hydrogenated forms of bchl aGG detectable, but the level of LH2 is increased and the red-shift reversed by several nm. We conclude that this gene, which we term chlP, encodes the enzyme catalysing the stepwise hydrogenation of geranylgeraniol to phytol during chla biosynthesis.