STUDY OF THE FUNCTION OF MED17 IN THE DNA DAMAGE RESPONSE AFTER UV-B

FREYTES S; CERDÁN P; GIUSTOZZI M; CASATI, P

Congreso; LVI Reunión Anual de SAIB; 2020

Solar radiation is very important for plants as it acts both as an energy source and as an environmental signal regulating growth and development. Solar radiation that reaches the earth?s surface is composed by visible light, UV-A radiation and also UV-B radiation. UV-B induces several effects on plant physiology, in particular DNA damage resulting in stress responses and inhibition of photosynthesis. In particular, when there is DNA damage, it is an activation of what is known as the DNA damage response, which is essential for survival.On the other hand, the Mediator complex is a conserved multi-protein complex that regulates transcription at the assembly of the transcription preinitiation complex. Structural studies in yeasts determinate that it is composed by four modules, head, middle, tail and Cyclin Dependent Kinase 8. In the head module, the subunit 17 interacts with the middle and tail modules. In Arabidopsis, mediator is composed by 34 subunits and acts as a signal integrator. Several reports show that MED17 connects transcription with DNA repair, in particular with the Nucleotide Excision Repair (NER) system. Moreover, in humans, MED17 interacts with the DNA helicase XPB, which is essential for both transcription and DNA repair. Then, the objective of this work is to study the role of MED17 in the DNA damage response after UV-B exposure in A. thaliana. We analyzed the med17 transcriptome changes under control conditions and we compared them with those occurring in WT plants after UV-B exposure. med17 plants showed decreased expression of particular UV-B up-regulated genes in WT plants. Thus, we analyzed DNA damage responses in med17 and WT plants. When we quantified DNA damage after UV-B exposure, med17 plants presented more DNA damage both under light and under dark conditions. When DNA damage is not repaired, then programmed death cell (PDC) is triggered. Interestingly, med17 plants showed that less PDC in the meristematic root cells than WT plants after UV-B exposure. Finally, with the aim to study the complementation of med17 mutants, we transformed med17 plants with a plasmid expressing Pro35S:MED17-GFP using the floral dip method. We compared the phenotypes of med17 mutants and the complemented med17 MED17OE; plants, both under control conditions and after UV-B exposure. Our results show a successful complementation of the med17 mutants when we analyzed root growth, flowering time and leaf morphology. Together, our results provide evidence of the participation of AtMED17 DNA damage responses after UV-B exposure.