Expression of a foreign gene in Chlamydomonas reinhardtii chloroplast

Chimeric genes for expression of a foreign gene in the Chlamydomonas reinha rdtii chloroplast were constructed. These chimeric genes are composed of th e promoter from chloroplast genes, rbcL, psbA, and atpA, 5'- and 3'-untrans lated regions, and the Escherichia coli beta-glucuronidase (GUS) structural gene (uidA) as a foreign gene. Three types of chloroplast transformants (R G, PG, and AG), which contained the rbcL-uidA, psbA-uidA, and atpA-uidA chi meric genes integrated in the chloroplast genome, were generated by particl e bombardment. The AG transformant grown under photoautotrophic conditions showed the highest GUS activity (130 nmol/min/mg protein) so far reported i n C. reinhardtii, and the accumulated GUS protein accounted for 0.08% of th e total soluble proteins. GUS activity in RG was 12% of that in AG, and no activity was detected in PG. We also measured the GUS activity from transfo rmants grown under heterotrophic conditions, but the culture conditions mad e little difference in activity levels. The difference in the amount of acc umulated GUS protein in the transformants was paralleled by the difference in the level of transcripts, and the pattern of gene expression was not the same as that of the endogenous genes in the chloroplast.