ASF1 Proteins are Involved in UV-induced DNA Damage Repair and are Cell Cycle Regulated by E2F Transcription Factors in Arabidopsis thaliana

Abstract

ASF1 is a key histone H3/H4 chaperone that participates in a variety of DNA and chromatin-related processes, including DNA repair, where chromatin assembly and disassembly is of primary<br />relevance. Information concerning the role of ASF1 proteins in post-UV response in higher plants is currently limited. In Arabidopsis thaliana, an initial analysis of in vivo localization of ASF1A and<br />ASF1B indicates that both proteins are mainly expressed in proliferative tissues. In silico promoter<br />analysis identified ASF1A and ASF1B as potential targets of E2F transcription factors. These<br />observations were experimentally validated, both in vitro by electrophoretic mobility shift assays, and in vivo by chromatin immunoprecipitation assays and expression analysis using transgenic plants with altered levels of different E2F transcription factors. These data suggest that ASF1A and ASF1B are regulated during cell cycle progression through E2F transcription factors. In addition, we found that ASF1A and ASF1B are associated with the UV-B induced DNA damage response in A. thaliana. Transcript levels of ASF1A and ASF1B were increased following a UV-B-treatment. Consistent with a potential role in ultraviolet-B (UV-B) response, RNAi silenced plants of both genes showed increased sensitivity to UV-B compared to wild type plants. Finally, by coimmunoprecipitation analysis, we found that ASF1 physically interacts with N-terminal acetylated histones H3 and H4, and with acetyltransferases of the HAM subfamily, which are known to be involved in cell cycle control and DNA repair, among other functions. Together, here we provide evidence that ASF1A and ASF1B are regulated by cell cycle progression and are involved in DNA repair after UV-B irradiation.