The gene family encoding the fucoxanthin chlorophyll proteins from the brown alga Macrocystis pyrifera

Six members of a multigene family encoding polypeptide constituents of the fucoxanthin, chlorophyll a/c protein complex from female gametophytes of the brown alga Macrocystis pyrifera have been cloned and characterized. The deduced amino acid sequences are very similar to those of fucoxanthin chlorophyll binding proteins (Fcp) from the diatom Phaeodactylum tricornutum and exhibit limited homology to chlorophyll a/b binding (Cab) polypeptides from higher plants. The primary translation products from the M. pyrifera fcp genes are synthesized as higher molecular weight precursors that are processed prior to their assembly into the Fcp complex. The presumed N-terminal 40-amino acid presequence of the Fcp precursor polypeptide has features resembling that of a signal sequence. This presequence may be required for the protein to transverse the endoplasmic reticulum that surrounds the plastid in brown algae. A subsequent targeting step would be required for the protein to cross the double membrane of the plastid envelope. M. pyrifera fcp transcripts are of two sizes, 1.2 and 1.6 kb. The size difference is accounted for by the length of the 3' untranslated region, which can be up to 1000 bases. Transcript abundance's of members of the fcp gene family are dependent on light quantity, light quality, or both. Transcript levels of one gene increased approximately five- to tenfold in thalli grown in low intensity relative to high intensity white or blue light. Transcripts from this gene also significantly increase in red light relative to blue light at equivalent light intensities.