Project description:Plants and algae have developed various light harvesting mechanisms for optimal delivery of excitation energy to the photosystems. The cryptophyte algae have evolved a novel soluble light-harvesting antenna utilizing phycobilin pigments to complement the membrane-intrinsic Chl a/c-binding LHC antenna. This new antenna consists of the plastid-encoded beta-subunit, a relict of the ancestral phycobilisome, and a novel nuclear-encoded -subunit unique to cryptophytes. Together, these proteins form the active tetramer, which consists of one alpha 1 and one alpha 2 and two beta susbunits. In all cryptophyte algae investigated so far, the alpha-subunits have duplicated and diversified into a large gene family. Although there is transcriptional evidence for expression of all these genes, the x-ray structures determined to date suggest that only two of the -subunit genes might be significantly expressed at protein level. Using proteomics, we show that phycoerythrin 545 (PE545) of Guillardia theta, the only cryptophyte with a sequenced genome, all 20 alpha-subunits are expressed when the algae grow under white light. Their relative expression levels depend on the intensity of the growth light, but there is no evidence for a specific light-dependent regulation of individual members of the alpha-subunit family under the growth conditions applied. Subunit GtcpeA10 seems to be a special member of the alpha-subunit family, because it consists of two similar N- and C-terminal domains, which likely are the result of a partial gene duplication.
