The chloroplast sulfate transport system in the green alga Chlamydomonas reinhardtii

Abstract

The genome of the model unicellular green alga Chlamydomonas reinhardtii contains four distinct genes, SulP, SulP2, Sbp and Sabc, which together are postulated to encode a chloroplast envelope-localized sulfate transporter holocomplex. In this work, evidence is presented that regulation of expression of SulP2, Sbp and Sabc is specifically modulated by sulfur availability to the cells. Induction of transcription and higher steady-state levels of the respective mRNAs are reported under S-deprivation conditions. No such induction could be observed under N or P deprivation conditions. Expression, localization, and complex-association of the Sabc protein was specifically investigated using cellular and chloroplast fractionations, BN-PAGE, SDS-PAGE and Western blot analyses. It is shown that Sabc protein levels in the cells increased under S-deprivation conditions, consistent with the observed induction of Sabc gene transcription. It is further shown that the Sabc protein co-localizes with SulP to the chloroplast envelope. Blue-native PAGE followed by Western blot analysis revealed the presence of an apparent 380 kDa complex in C. reinhardtii, specifically recognized by polyclonal antibodies against SulP and Sabc. These results suggest the presence and function in C. reinhardtii of a Sbp-SulP-SulP2-Sabc chloroplast envelope sulfate transporter holocomplex.

Mechanism of REP27 Protein Action in the D1 Protein Turnover and Photosystem II Repair from Photodamage

“…5, S). Resolved thylakoid membranes and isolation of a light membrane fraction, including the chloroplast envelopes, was achieved by differential ultracentrifugation, as recently done in this laboratory (Lindberg and Melis, 2008). Western-blot analysis of these membrane fractions with REP27-specific antibodies showed presence of the REP27 protein in the thylakoid membrane fraction and absence from the lighter envelope-containing fraction (data not shown).…”

Identification and Regulation of Plasma Membrane Sulfate Transporters in Chlamydomonas

“…A distinct permease involved in translocating SO 4 22 from the cytoplasm into chloroplasts is composed of the subunits SulP1, SulP2, Sabc, and Sbp (Melis and Chen, 2005). Expression of all four genes encoding the components of this permease is induced upon S deprivation; levels of SulP and Sabc polypeptides also increase when the cells become S limited (Lindberg and Melis, 2008). …”

“…Transcripts from some of the transporter genes increase significantly during S deprivation; increased accumulation of SLT1 and SULTR2 transcripts during S starvation was previously reported (Gonzalez-Ballester et al, 2008). Chlamydomonas also possesses SO 4 22 permeases (SulP1 and SulP2) that resemble the permeases of bacteria (Laudenbach and Grossman, 1991;Chen et al, 2003;Lindberg and Melis, 2008). These transport proteins have been localized to the chloroplast envelope and function in the transport of SO 4 22 from the cytosol into chloroplasts, where reductive assimilation of the anion occurs.…”

A new approach for sustained and efficient H2 photoproduction by Chlamydomonas reinhardtii

“…9 Although the loss of active PSII centers sustains H 2 photoproduction in algae, it also downregulates the direct, water oxidation-dependent flow of electrons to the H 2 ase, resulting in low overall efficiency of the process. Sulfurdeprivation requires extensive and time-consuming centrifugations, which make this protocol difficult for application even in laboratory scale projects (yet a few alternatives have been suggested 10,11 ).…”