DIFFERENTIALSUBNUCLEAR LOCALIZATION

OF THE MBD4LDNA GLYCOSYLASE SPLICING ISOFORMS.

POSSIBLEROLE(S) ON STRESS RESPONSES.

Nicolas M Cecchini, Jose R Torres,Florencia Nota, Santiago

Cobo, Maria EAlvarez

DNA glycosylases are key enzymes for organisms? genomestabilitymediating DNA damage repair. Among them, MBD4L is a nuclearArabidopsisDNA glycosylase acting during stress conditions.Interestingly, MBD4L genecan generate two-isoforms through theretention of a protein-coding crypticintron (exitron). It is believedthat exitron splicing events result in proteinversions with alternativefunctional domains and/or post-translationalmodifications. Taking this into account, we analyzed MBD4L splicing-isoformstranscript levels, subcelular localization and contribution to damaged DNAcorrection.We found that the MBD4L alternative transcripts changed theirrelative levels depending on the stress applied. Surprisingly,when expressed asGFP fusions each of the MBD4 isoforms located at different subnuclearcompartments in both Arabidopsis and Nicotiana benthamiana plants.Moreover, some stresses induced dynamic changes in enzyme subnuclearlocalization. On the otherhand, although showing distinctive localization theoverexpression of both MBD4L isoforms increased resistance to a DNA damaging agent.Altogether, our results indicate that MBD4L location can be

driven by exitron alternative splicing mechanisms. However, additional levelsof control may determine differential subcellular requirements for MBD4Lisoforms under particular circumstances. A putative model for MBD4L nuclearrole/localization will be presented