Elongin C complexes in Arabidopsis development and DNA repair

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Plants depend on sunlight for survival, yet sunlight consists of not only beneficial visible light but also damaging ultraviolet (UV) rays. I am interested in how plants optimize their response to visible light while protecting themselves from UV damage. Here I propose to examine the role of Elongin C complexes in light-regulated developmental transitions, such as flowering, as well as in UV-damaged DNA repair. All organisms must protect their genomes (DNA) from UV damage. Amazingly, life-forms from yeast to plants to humans use basically the same process to do this: a pathway called Nucleotide Excision Repair, where UV-damaged DNA is recognized, unwound, cut and repaired. The only step in this process that varies between organisms is the initial damage recognition. In the baker’s yeast Saccharomyces cerevisiae damage recognition and initiation of repair is performed by the Radiation Sensitive (RAD) 7 / RAD16 / Elongin C (ELC1) complex. In mammals (including humans) however, damaged DNA is recognized by Damaged DNA Binding protein (DDB) 1 & 2. In plants, work by my lab and other researchers has shown that DDB1&2 are involved in repair of plant UV-damaged DNA. Interestingly, recent bioinformatic analysis in the model plant Arabidopsis thaliana has revealed that plants also have RAD7, RAD16, and ELC1 proteins, but their functions are uncharacterized. This provides us with a unique opportunity to examine the roles and interactions of both the mammalian (DDB1&2) and yeast (RAD7&16) damaged DNA recognition factors in a single system. I propose to use the extensive molecular and genetic tools available to Arabidopsis researchers to examine the role of the RAD7/RAD16/ELC1 complex in plant UV tolerance and DNA repair. Specifically, we will generate genetic material with altered levels of these genes then analyze developmental, UV tolerance and DNA repair phenotypes. In addition, we will examine RAD7, RAD16 and ELC1 protein levels, interaction partners and location in the cell as well as regulation of these properties by UV. Excitingly, our preliminary results show that rad7a, rad7b, and rad16b mutants are all UV-sensitive, supporting our hypothesis and providing the first evidence in any multicellular organism of a role for the RAD7 complex in DNA repair. In addition, by analyzing development in our mutants, we have found that rad16 and elongin c mutants are early flowering. Thus the role of plant Elongin C complexes seems to extend beyond DNA repair to regulation of important growth parameters. In yeast and mammals Elongin C interacts not only with RAD7, but also with Elongin A. The Elongin A/C complex regulates transcript (RNA) elongation. We have identified a possible Arabidopsis Elongin A and are also interested in its function in plants and potential contribution to Elongin C’s role in flowering time. Thus by examining the roles of these two prospective Elongin C complexes (RAD7- and Elongin A-containing) we will identify novel components of plant UV-damaged DNA repair as well as identify unique plant-specific roles for these conserved proteins, such as the regulation of flowering time. In this way we will gain insight into plant environmental response with respect to both stress (e.g. UV) and developmental (e.g. flowering time) cues. This research may lead to future crops with optimized UV tolerance and genome stability.