Fig. 4. Activation of the DNA damage response pathway in Arabidopsis csn mutants. (A) Differential expression of genes with a predicted role in DNA repair in response to DNA-damaging agents (1.5 µg/ml bleomycin + 22 µg/ml mitomycin) in the wild type, and their expression in dark- and light-grown csn mutants (Benjamini Hochberg false discovery rate <0.05, 2-fold differential expression; see also Table S2 in the supplementary material). The expression of BRCA1, PARP1 and RAD51 was independently verified by RT-PCR (see Fig. S1 in the supplementary material). (B) GUS-staining of wild-type and csn mutant seedlings expressing the DNA damage reporter PARP2:GUS. PARP2:GUS expression is induced in csn mutants and in the wild type following a 12-hour treatment with the DNA-damaging agent bleomycin (5 µg/ml). Scale bars: 2 mm.