Identification and regulation of Chlamydomonas sulfate transporters

Wirulda Pootakham1,2, David Gonzalez-Ballester2, and Arthur R. Grossman2

1) Stanford University, Department of Biology, Stanford, CA 94305 2) The Carnegie Institution, Department of Plant Biology, 260 Panama Street, Stanford, CA 94305

Chlamydomonas reinhardtii (Chlamydomonas) exhibits several responses following exposure to sulfur (S)-deprivation conditions, including an increased efficiency of import and assimilation of the sulfate anion (SO42-). Aspects of SO42- transport during S-replete and S-depleted conditions were previously studied, although the transporters had not been functionally identified. We employed a reverse genetic approach to identify putative SO42- transporters, examine their regulation, establish their biogenesis and subcellular locations, and explore their functionality. Upon S starvation of wild-type Chlamydomomas cells, the accumulation of transcripts encoding the putative SO42- transporters SLT1, SLT2, and SULTR2, markedly increased, suggesting that these proteins function in high-affinity SO42- transport. The Chlamydomonas sac1 and snrk2.1 mutants (defective for acclimation to S deprivation) exhibited much less of an increase in the levels of SLT1, SLT2 and SULTR2 transcri pts and their encoded proteins in response to S deprivation compared to wild-type cells. All three transporters were localized to the plasma membrane and their rates of turnover were significantly impacted by S availability; the turnover of SLT1 and SLT2 was proteasome dependent while that of SULTR2 was proteasome independent. Finally, mutants identified for each of the S-deprivation-responsive transporters were used to establish their critical role in the transport of SO42- into S-deprived cells.

e-mail address of presenting author: wirulda@stanford.edu