Just as the universe is filled with mysterious and unexplained matter, so living cells are filled with small RNAs – the “dark matter” of genetics. Plants cells contain hundreds of thousands of these tiny molecules but only for a few of them is there a known function. Cambridge University scientists recently discovered a surprising characteristic of small RNAs in plants. In an article published online today in the journal Nature, researchers led by Professor David Baulcombe describe maternal-specific expression of the most abundant class of small RNAs in developing seeds. Although the small RNAs are produced from cells containing genes from both parents, only the maternal genes are active. Scientists have known for decades that organisms have a molecular memory of which genes they have inherited from each parent and this “imprint” is of critical importance in a number of human diseases. However, very little is known about the nature of imprinting or why such a mechanism would evolve. Dr. Rebecca Mosher, a senior researcher in the group, suggests that imprinted expression of small RNAs indicates large-scale genetic control by the mother – perhaps an evolutionary example of over-parenting.
Read the publication in Nature
A developing seed contains two cell types with maternal DNA – the endosperm (green area) and the embryo (brown). The maternal (purple edge) and paternal (brown) genomes are both active but only the maternal genomes generate small RNA (purple line).