LIGHT-REGULATED TRANSCRIPTION OF GENES ENCODING PERIDININ CHLOROPHYLL-A PROTEINS AND THE MAJOR INTRINSIC LIGHT-HARVESTING COMPLEX PROTEINS IN THE DINOFLAGELLATE AMPHIDINIUM-CARTERAE HULBURT (DINOPHYCAE) - CHANGES IN CYTOSINE METHYLATION ACCOMPANY PHOTOADAPTATION

In the dinoflagellate Amphidinium carterae, photoadaptation involves c hanges in the transcription of genes encoding both of the major classe s of light-harvesting proteins, the peridinin chlorophyll a proteins ( PCPs) and the major a/c-containing intrinsic light-harvesting proteins (LHCs). PCP and LHC transcript levels were increased up to 86- and 6- fold higher, respectively, under low-light conditions relative to cell s grown at high illumination. These Increases in transcript abundance were accompanied by decreases in the extent of methylation of CpG and CpNpG motifs within or near PCP- and LHC-coding regions. Cytosine meth ylation levels in A. carterae are therefore nonstatic and may vary wit h environmental conditions in a manner suggestive of involvement in th e regulation of gene expression. However, chemically induced undermeth ylation was insufficient in activating transcription, because treatmen t with two methylation inhibitors had no effect on PCP mRNA or protein fevers. Regulation of gene activity through changes in DNA methylatio n has traditionally been assumed to be restricted to higher eukaryotes (deuterostomes and green plants); however, the atypically large genom es of dinoflagellates may have generated the requirement for systems o f this type in a relatively ''primitive'' organism. Dinoflagellates ma y therefore provide a unique perspective on the evolution of eukaryoti c DNA-methylation systems.