A New Mediator of Singlet Oxygen Responses in Chlamydomonas and Arabidopsis

We identified a small zinc finger protein, MBS, as a new mediator of singlet oxygen responses in Chlamydomonas and Arabidopsis. MBS is required for induction of singlet oxygen-dependent gene expression and, upon oxidative stress, accumulates in distinct granules in the cytosol of Arabidopsis cells. First, we recorded changes in light stress-regulated gene expression profiles after genetically perturbing MBS function by isolating mutants for the two MBS genes (MBS1 and MBS2) and by overexpression of MBS1 in Arabidopsis thaliana. Then, these light stress-related gene expression profiles were analyzed with respect to genes specifically responding to singlet oxygen and hydrogen peroxide/superoxide. The results indicated that MBS inactivation leads to an impaired response to singlet oxygen signaling under light stress. Knock-out or knock-down of the MBS1 and MBS2 genes and overexpression of MBS1 in Arabidopsis thaliana were compared with the wild type and the flu mutant as controls under light stress. Arabidopsis seedlings of mbs1-1, RNAi-MBS2/mbs1-1, 35S:MBS1, the wild type and the flu mutant were harvested at 0 h and 3 h of light stress (HL, 1000 µE m−2 s−1). Total RNA was extracted and cDNA was hybridized to Affymetrix ATH1 microarrays in three biological replicates.