Elucidating the biological function of Arabidopsis DASH-type cryptochrome

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DASH-type cryptochromes constitute the most recently discovered subclade of the cryptochrome/photolyase family. Cryptochromes are blue-light photoreceptors, whereas DNA photolyases repair UV lesions in DNA. DASH-type cryptochromes have been identified in plants, fungi, many bacteria, eumetazoa, and aquatic vertebrates (e.g., fish, amphibians). In vitro, they repair UV-B lesions in single-stranded and loop-structured DNA. However, the UV-B sensitivity of photolyase-deficient Escherichia coli is not rescued by complementation with DASH-type cryptochromes. Likewise, Arabidopsis thaliana mutants deficient in cry-DASH (cry3) are phenotypically indistinguishable from wild type under normal growth-chamber conditions and also when treated with UV-B. Thus, an in vivo function of DASH-type cryptochromes as DNA-repair enzymes remains obscure. We propose to decipher the biological role of A. thaliana cry3 using a combination of genetic, biochemical, and physiological techniques. We will attempt to determine whether cry3 acts solely as a photoreceptor or as a repair enzyme, or has a dual function in both processes or a novel function not yet implicated for members of the cryptochrome/photolyase family. In particular, we will search for putative cry3-interacting proteins and study macroscopic and molecular phenotypes of cry3 mutants in genetic backgrounds lacking also cryptochromes or photolyases.