Heavy-metal regulation of thioredoxin gene expression in chlamydomonas reinhardtii
Heavy metals are highly toxic compounds for cells. In this report we demonstrate that the expression of Chlamydomonas reinhardtii thioredoxins (TRX) m and h is induced by heavy metals. Upon exposure of the cells to Cd and Hg, a strong accumulation of both messengers was observed. Western-blot experiments revealed that among these two TRXs, only TRX h polypeptides accumulated in response to the toxic cations. A biochemical analysis indicated that heavy metals inhibit TRX activity, presumably by binding at the level of their active site. Sequence analysis of the C. reinhardtii TRX h promoter revealed the presence of cis-acting elements related to cadmium induction. The origins and purposes of this regulation are discussed. Our data suggest, for the first time to our knowledge, a possible implication of TRXs in defense mechanisms against heavy metals.
Institut de Biotechnologie des Plantes, Unite Mixte de Recherche 8618, Centre National de la Recherche Scientifique, Universite Paris-Sud, Batiment 630, 91405 Orsay cedex, France (S.L., E.K., M.S. , I.S., E.I.-B., C.G.-H., M.M.-M.).
S
Lemaire
E
Keryer
M
Stein
I
Schepens
E
Issakidis-Bourguet
G rard-Hirne C
M
Miginiac-Maslow
JP
Jacquot