In any living organism, all cells have the same DNA, but each cell's identity is defined by the combination of genes that are turned on or off, any given moment in time. In animals, this cellular memory is erased between generations, so that the new egg has no memory and, as such, has the potential to become any type of cell. In flowering plants, on the contrary, cellular memory passes from generation to generation, with potentially harmful implications for the development of new plants. In the latest issue of the journal Cell*, scientists from Instituto Gulbenkian de Cincia (IGC), in Portugal, and Cold Spring Harbor Laboratory (CSHL), in the USA, describe a novel mechanism whereby potentially mutagenic sequences of mobile DNA are silenced in the pollen grain and in seeds, thus avoiding damage to new plants.
One of the main mechanisms that contributes to cellular memory is the addition of a chemical group - the methyl group - to DNA sequences (a process called methylation). DNA methylation turns a gene off. These changes in gene expression that are heritable, but not directly written in the DNA sequence, are called epigenetics. Using the plant model Arabidopsis thaliana, Jrg Becker, Jos Feij and their team, at the IGC, and Robert Martienssen and colleagues, at CSHL, analysed the genome of pollen grains and their precursor cells, the microspores, and pinpointed the sequences of DNA that were methylated. Pollen grains contain two sperm cells (the sexual cells) and an accompanying vegetative nucleus, whose DNA is not passed on to the next generation. Thanks to the technique developed by the IGC team, the researchers were able to separate the two sperm cells and the vegetative nucleus of the pollen grain and look at their methylation status separately.
Joseph Calarco (in the Martienssen lab
|Contact: Ana Mena|
Instituto Gulbenkian de Ciencia