Expression analysis of the singlet oxygen resistant 1 (sor1) mutant

In a screen for singlet oxygen resistant mutants, a mutant called sor1 was isolated with increased resistance to different oxidative and electrophilic stress conditions. This mutant was found to have a constitutive high expression of three known singlet oxygen response genes, a glutathione peroxidase GPX5 and two glutathione-S-transferase GSTS1 and GSTS2. The sor1 mutation was mapped to the gene of a 393-amino acid protein for which blast searches revealed only poor homology to other proteins but predicted a putative basic leucine zipper DNA binding domain indicating that it might function as transcription factor to activate gene expression during oxidative stress.Global expression analysis of sor1 compared to the untreated wild-type enabled to identify additional genes differentially regulated in the sor1 mutant including several other genes involved in oxidative stress response and detoxification of endogenous xenobiotics. The sor1 mutant and the corresponding wild-type strain 4A+ were grown mixotrophically in a Tris-acetate phosphate in three independent biological replicates. Then the cells of each replicate were harvested by centrifugation and total RNA was isolated using the RNeasy Mini Kit (Qiagen). DNA microarrays were performed using the ‘One-Color Microarray-Based Gene Expression Analysis’ system and a custom made 4 × 44 K ‘Chlamydomonas Whole Genome DNA Microarrays’ (Agilent Technologies) containing 15143 specific probes designed based on the Chlamydomonas version 4.0 transcript models provided by the DOE Joint Genome Institute (JGI), with an average of three replicates for each probe