DNA transfer from chloroplast to nucleus is much rarer in Chlamydomonas than in tobacco

By transforming chloroplasts with an antibiotic-resistance gene under the control of a nuclear-specific promoter, we employed a selection scheme to detect the transfer of DNA from the chloroplast to the nucleus in the green alga Chlamydomonas reinhardtii. Among several billion homoplasmic cells tested, we were unable to detect any stable nuclear integration of chloroplast DNA under normal growth conditions or under stress conditions. This contrasts with results reported for the transfer of DNA from chloroplast to nucleus in higher plants and from mitochondrion to nucleus in Saccharomyces cerevisiae. Furthermore, we were unable to detect chloroplast DNA-derived sequences among nuclear genome data for C. reinhardtii, which also contrasts with the situation in higher plants. Taken together, these findings suggest that there is presently little, if any, movement of DNA from chloroplast to nucleus in C. reinhardtii, which may reflect the ultrastructure of the C. reinhardtii cell.