RESPONSE OF MSH6 MISMATCH REPAIR PROTEIN TO LIGHT SIGNALS

GONZALEZ, VALENTINA; SPAMPINATO, CLAUDIA P.

Congreso; Reunión conjunta SAIB SAMIGE; 2020

The mismatch repair (MMR) system is a highly conserved pathway that plays a key role in maintaining genome stability. The first step of the pathway involves recognition of the mismatch by heterodimers composed of MutS homologs (MSH). Although MSH6 has been well characterized in yeasts and humans, specific roles of the protein in plants remain to be studied. An in silico analysis of the promoter region of Arabidopsis thaliana MSH6 (pAtMSH6) indicated the presence of three putative binding regions of the SORLIP type (sequences over-represented in light-induced promoters), one SORLIP2 (GGGCC) and two SORLIP5 (GAGTGAG). These sequences have been found in hundreds of genes that are transcriptionally regulated by phytochrome A (PHYA). A. thaliana has five phytochromes, known as PHYA to PHYE, being PHYA responsible for the far red light detection. Thus, we first investigated the effect of light signals on pAtMSH6:GUS expression. Our results indicate that GUS expression level was significantly induced after 8 h light induction. Then, we analyzed the light specificity and photoreceptors involved in regulating the MSH6 response to light. Quantitative RT-PCR (qRT-PCR) analysis show that MSH6 expression decreased in single phyA, single phyB and double phyA/phyB mutants compared to wild type plants. In addition, pAtMSH6:GUS expression was downregulated in phyA and phyA/phyB mutant plants. These results suggest that far red light may be responsible for the induction of MSH6. An in-depth in silico and comparative analysis of MSH6 promoters across Brassicaceae highlights two highly conserved regions (RI extending from -50 to -200 bp of pAtMSH6 and RII extending from -850 to -900 bp of pAtMSH6). RI includes binding sites for E2F transcription factors, studies already carried out in our lab, and RII comprises GATA and bHLH motifs. Thus, two constructions pAtMSH6-690:GUS and AtpMSH6-207:GUS were generated. The first construction lacks the RII and the second, two SORLIP sequences. A. thaliana plants transformed with these constructions show no GUS staining. This result indicates that region II is essential for MSH6 expression. Taken together, this study shows that light signals induce MSH6 expression. Further research is needed to elucidate transcription factors involved in gene regulation.