Submitted to: American Society of Plant Physiologists Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 3/20/2000
Publication Date: N/A
Technical Abstract: At harvest, potato tuber meristems (eyes) are incapable of growth due to endogenous physiological factors. Tuber dormancy is broken only after a period of postharvest storage. Prevention of sprouting is a major objective of the potato industry but the molecular mechanisms leading to dormancy break are unknown. Dormant meristems exhibit low rates of RNA synthesis and the onset of sprout growth is accompanied by an increase in transcriptional activity. In many species, DNA is frequently methylated after replication, often on cytosine residues in the sequences CpG or, in plants, CpNpG (where N is any nucleotide except G). Alteration in DNA methyl-cytosine content has been shown to occur during development and may modulate gene expression in plants and animals. We have investigated DNA methylation status in field-grown tuber meristems throughout an 8-month postharvest storage period. Genomic DNA was extracted from meristems from 3 field seasons and cut with methylation- sensitive or -insensitive isochizometric restriction enzyme pairs. Southern blots of this digested DNA examined for RNA polymerase 18S and 28S subunits using a pea probe indicated that methylation status of these genes was unaltered during dormancy break. To examine genome-wide methylation differences, the digested DNA was monitored for radiolabel incorporation of [3H]CTP using DNA polymerase in a nucleotide extension assay. A consistent 2- to 3-fold increase in DNA demethylation at these restriction sites was observed 100 to 140 d postharvest. These results indicate that transcriptional activation may be quite selective upon dormancy break, and future studies using a chemical method and AFLP analysis are currently being conducted.