Role of MED17, a subunit of the Mediator complex, in DNA damage responses after UV-B exposure in Arabidopsis

GIUSTOZZI, MARISOL; FREYTES, SANTIAGO N.; LICHY, MICAELA; JASKOLOWSKI, AIME; LORENZI, HERNAN; MATEOS, JULIETA; CERDÁN, PABLO; CASATI P.

Congreso; 1st virtual Meeting of the UV4Plants Association; 2020

UV-B levels that reach the earth can cause damage to proteins, lipids, RNA and DNA, inducing different responses in plants. Because of their sessile lifestyle, plants have developed defense mechanisms against this damage. One of the response pathways to DNA damage in plants involves the activation of two different protein kinases: Ataxia Telangiectasia Mutated (ATM; which mostly recognizes double strand breaks in the DNA); and Ataxia Telangiectasia mutated and RAD3-related (ATR; which mostly recognizes single strand damage and DNA crosslinks). Both kinases can activate by phosphorylation Suppressor of Gamma Response 1 (SOG1), which is a transcription factor that regulates the expression of genes involved in cell cycle transitions, DNA repair and chromatin structure. The Mediator complex functions as a molecular bridge between transcriptional activators and the DNA-bound RNA polymerase II. Interestingly, several reports have demonstrated that the yeast and human Mediator subunit 17 (MED17) also acts as a regulator of DNA repair. In our lab, we have recently demonstrated that A. thaliana med17 mutants also show higher DNA damage after UV-B exposure than WT plants, and that UV-B exposure to roots induces a lower accumulation of dead meristematic cells in med17 seedlings than WT plants. Interestingly, the transcriptome analysis of med17 mutants showed that transcripts that encode proteins in the UVR8 signaling pathway are down-regulated, suggesting that MED17 mediates different UV-B responses in Arabidopsis.In this talk, data on the role of MED17 in the DNA damage response in Arabidopsis plants and its possible interaction with ATM and ATR pathways will be presented. Our results demonstrate that, similarly as to what occurs in other organisms, Arabidopsis MED17 has an important role in the DNA damage response under UV-B conditions, and that its role is epistatic over ATR.