Poster: Membrane transport

Abs # 173: Localization and function of SulP, a nuclear-encoded chloroplast sulfate permease in Chlamydomonas reinhardtii

Presenter:	Chen, Hsu-Ching , hcwintz@nature.berkeley.edu
Authors	Chen, Hsu-Ching  (A)   Melis, Anastasios  (A)
Affiliations:	(A): University of California, Berkeley

A novel nuclear-encoded sulfate permease gene (SulP) was cloned in the green alga Chlamydomonas reinhardtii (Planta 218: 98-106, 2003). Genomic, proteomic, phylogenetic and evolutionary analyses suggested a sulfate permease gene of prokaryotic origin. In an effort to elucidate the localization and function of the SulP protein, specific polyclonal antibodies were raised against the recombinant protein. These were used in Western blot analyses of isolated cellular and chloroplast fractions. Evidence is provided for the localization of the SulP in the chloroplast envelope of this green alga. Antisense technology with the SulP gene and sulfur deprivation studies were employed as tools in combination with measurements of photosynthesis, rates of sulfate uptake and properties of the photosynthetic apparatus in an effort to investigate functional aspects of the SulP gene. Evidence is provided that cellular sulfate uptake capacity is lowered as a consequence of attenuated SulP gene expression in the antisense transformants, directly affecting rates of de novo protein biosynthesis. The antisense transformants exhibited phenotypes of sulfur-deprived cells, displaying slow rates of light-saturated oxygen evolution, low levels of Rubisco in the chloroplast, and low steady state levels of the photosystem-II D1 reaction center protein. These results constitute a first-time report on the functional properties of a chloroplast sulfate transport system. The role of SulP in the uptake and assimilation of sulfate in C. reinhardtii is discussed along with its impact on the repair of the photosynthetic apparatus from a frequently occurring photo-oxidative damage and its potential use as a tool in the elucidation of the regulation of H₂-evolution metabolism in this green alga.