Identification of Lhcb gene family encoding the light-harvesting chlorophyll-a/b proteins of photosystem II in Chlamydomonas reinhardtii

The Lhcb gene family in green plants encodes several light-harvesting Chl a /b-binding (LHC) proteins that collect and transfer light energy to the rea ction centers of PSII. We comprehensively characterized the Lhcb gene famil y in the unicellular green alga, Chlamydomonas reinhardtii, using the expre ssed sequence tag (EST) databases. A total of 699 among over 15,000 ESTs re lated to the Lheb genes were assigned to eight, including four new, genes t hat we isolated and sequenced here. A sequence comparison revealed that six of the Lheb genes from C. reinhardtii correspond to the major LHC (LHCII) proteins from higher plants, and that the other two genes (Lhcb4 and Lhcb5) correspond to the minor LHC proteins (CP29 and CP26). No ESTs correspondin g to another minor LHC protein (CP24) were found. The six LHCII proteins in C. reinhardtii cannot be assigned to any of the three types proposed for h igher plants (Lhcb1-Lhcb3), but were classified as follows: Type I is encod ed by LhcII-1.1, LhcII-1.2 and LhcII-1.3, and Types II, III and IV are enco ded by LhcII-2, LhcII-3 and LhcII-4, respectively. These findings suggest t hat the ancestral LHC protein diverged into LHCII, CP29 and CP26 before, an d that LHCII diverged into multiple types after the phylogenetic separation of green algae and higher plants.