CK2-defective Arabidopsis plants exhibit enhanced double-strand break repair rates and reduced survival after exposure to ionizing radiation

The multifunctional protein kinase CK2 is involved in several aspects of the DNA damage response (DDR) in mammals. To gain insight into the role of CK2 in plant genome maintenance, we studied the response to genotoxic agents of an Arabidopsis CK2 dominant-negative mutant (CK2mut plants). CK2mut plants were hypersensitive to a wide range of genotoxins that produce a variety of DNA lesions. However, they were able to activate the DDR after exposure to ? irradiation, as shown by accumulation of phosphorylated histone H2AX and up-regulation of sets of radio-modulated genes. Moreover, functional assays showed that mutant plants quickly repair the DNA damage produced by genotoxins, and that they exhibit preferential use of non-conservative mechanisms, which may explain plant lethality. The chromatin of CK2mut plants was more sensitive to digestion with micrococcal nuclease, suggesting compaction changes that agreed with the transcriptional changes detected for a number of genes involved in chromatin structure. Furthermore, CK2mut plants were prone to transcriptional gene silencing release upon genotoxic stress. Our results suggest that CK2 is required in the maintenance and control of genomic stability and chromatin structure in plants, and that this process affects several functions, including the DNA damage response and DNA repair.