DECONDENSATION OF ARABIDOPSIS CENTROMERES CAUSED BY EARLY PSEUDOMONAS INFECTION

PAVET V; CECCHINI NM; ÁLVAREZ ME

Congreso; SAIB - XL Annual Meeting ARGENTINE SOCIETY FOR BIOCHEMISTRY AND MOLECULAR BIOLOGY XL Reunión Anual SOCIEDAD ARGENTINA DE INVESTIGACIÓN BIOQUÍMICA Y BIOLOGÍA MOLECULAR; 2004

Methylation of cytosine residues is a key process for regulation ofchromatin structure and gene expression in several species. Wehave previously demonstrated that the Arabidopsis genome displaya 70% reduction of 5-methyl cytosine (5-mC) content at 24 hourspost-infection with Pseudomonas. The main targets of thismodification are CpG and/or asymmetric cytosines located inArabidopsis centromeric regions. Although transcriptional activityof pericentric coding sequences is not substantially altered, wehere demonstrate that 5-mC loss causes main changes in thechromatin organization of intephasic nuclei from infected cells.DAPI staining combined with inmunolabelling of 5-mC withmonoclonal antibodies showed that reduction of 5-mC residues atcentromeres precedes decondensation of these heterochromaticregions. Both responses were only observed at the inoculation sitesof infected tissues but not at distal sites of challenged leaves.Neither molecular markers of cell cycle progression nor BrdUincorporation was detected at bacterial-treated tissues, indicatingthat an active demethylation mechanism might operate. Whetherthis event is part of Pseudomonas pathogenicity strategies or it isinvolved in Arabidopsis defense responses remains to beelucidated.