Characterization of CrMRP2 and CrPMA2 genes involved in heavy metals resistances in chlamydomonas reinhardtii

Heavy metals are serious environmental pollutants due to their toxicities and bioaccumulation effects. In this study, genes related to heavy metal responses in Chlamydomonas reinhardtii, a unicellular green algae model species with its entire genome sequenced, were characterized. Cadmium (Cd) is one of the major metal pollutants. Two mutant strains, Cds18 and CdrB2 with Cd sensitive and resistance respectively, were generated by insertational mutagensis in our laboratory previously. In mutant Cds18, CrMRP2 coding for an ABC transporter and in CdrB2, CrPMA2 coding for a P type ATPase were altered by the insertion. I performed a metal(loid)s resistance assay for both strains using the wild type strain C. reinhardtii 950 as control. Cds18 was sensitive to all the metal(loid)s studied, indicating the multi-metals responses of CrMRP2. CdrB2 showed responses to particular metals, in addition to Cd, the strain was resistance to Nickel (Ni) and Zinc (Zn) among the metal(loid)s tested. Expression of CrMRP2-GFP fusion protein in S. cerevisiae illustrated the vacuolar localization of gene products in yeast. The transcriptions of the two genes upon Cd, Ni and Zn stimulations were studied and related to the metal contents incorporated into wild type, Cds18 and CdrB2 cells. In wild type cells, CrMRP2 transcription can be induced by Cd, Ni and Zn. Wild type cells with CrMRP2 functioning has a higher ability to detoxify intracellular metal content. While the transcription of altered CrPMA2 is induced by Cd, Ni and Zn, metal contents in CdrB2 declined in late part of metal exposure. The information of this study contributed to the understanding of cellular detoxification mechanisms for heavy metals in photosynthetic organisms