Tomato fruit cells are characterized by a strong increase in nuclear ploidy 
during fruit development. Average ploidy levels increased to similar levels 
(above 50C) in two distinct fruit tissues, pericarp and locular tissue. However, 
ploidy profiles differed significantly between these two tissues suggesting a 
tissue-specific control of endoreduplication in tomato fruit. To determine 
possible relationships between endoreduplication and epigenetic mechanisms, the 
methylation status of genomic DNA from pericarp and locular tissue of tomato 
fruit was analysed. Pericarp genomic DNA was characterized by an increase of CG 
and/or CNG methylation at the 5S and 18S rDNA loci and at gyspsy-like 
retrotransposon sequences during fruit growth. A sharp decrease of the global 
DNA methylation level together with a reduction of methylation at the rDNA loci 
was also observed in pericarp during fruit ripening. Inversely, no major 
variation of DNA methylation either global or locus-specific, was observed in 
locular tissue. Thus, tissue-specific variations of DNA methylation are unlikely 
to be triggered by the induction of endoreduplication in fruit tissues, but may 
reflect tissue-specific ploidy profiles. Expression analysis of eight putative 
tomato DNA methyltransferases encoding genes showed that one chromomethylase 
(CMT) and two rearranged methyltransferases (DRMs) are preferentially expressed 
in the pericarp during fruit growth and could be involved in the locus-specific 
increase of methylation observed at this developmental phase in the pericarp.