Identification and regulation of plasma membrane sulfate transporters in Chlamydomonas.
Chlamydomonas (Chlamydomonas reinhardtii) exhibits several responses following exposure to sulfur (S)-deprivation conditions, including an increased efficiency of import and assimilation of the sulfate anion (SO(4)(2-)). Aspects of SO(4)(2-) transport during S-replete and S-depleted conditions were previously studied, although the transporters had not been functionally identified. We employed a reverse genetics approach to identify putative SO(4)(2-) transporters, examine their regulation, establish their biogenesis and subcellular locations, and explore their functionality. Upon S starvation of wild-type Chlamydomonas cells, the accumulation of transcripts encoding the putative SO(4)(2-) transporters SLT1 (for SAC1-like transporter 1), SLT2, and SULTR2 markedly increased, suggesting that these proteins function in high-affinity SO(4)(2-) 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 transcripts and their encoded proteins in response to S deprivation compared with 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 SO(4)(2-) into S-deprived cells.
Pootakham
Wirulda
W
Department of Biology, Stanford University, Stanford, California 94305-5020, USA. wirulda@gmail.com
Gonzalez-Ballester
David
D
Grossman
Arthur R
AR
D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism*; D016825:Chlamydomonas reinhardtii / Q000235:genetics* / Q000378:metabolism; D015723:Gene Library; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D048030:RNA, Algal / Q000235:genetics; D013431:Sulfates / Q000378:metabolism; D013455:Sulfur / Q000378:metabolism*
D020418:Algal Proteins; D026901:Membrane Transport Proteins; D048030:RNA, Algal; D013431:Sulfates; D013455:Sulfur; D046988:Proteasome Endopeptidase Complex