Abstract
Sulfoquinovosyl diacylglycerol (SQDG) is present in photosynthetic membranes of most of oxygenic photosynthetic organisms. We here investigated regulation of SQDG metabolism in C. reinhardtii under the sulfur-deprived condition. Cells of C. reinhardtii degraded SQDG concomitantly with removal of sulfur source from the culture. This induction of the degradation was inhibited by actinomycin D or cycloheximide, suggesting that the induction requires de novo synthesis of protein(s) encoded in the nuclear genome. On the other hand, a trace level of SQDG still remained. In line with this, the capacity of SQDG synthesis was kept at the initial level and the mRNA level of the SQD1 gene for SQDG synthesis was increased. This up-regulation of the mRNA level was shown to require de novo protein synthesis through experiments with cycloheximide. These results implied that genes responsible for SQDG synthesis and degradation are simultaneously upregulated in their expression under the sulfur-deprived condition.
