A gene-switching mechanism dating back 400 million years to the very first plants that made it onto land has been found by plant biologists at UC Davis. A family of genes required for stem and leaf development in flowering plants is controlled in the same way in everything from mosses to a Douglas fir, according to postdoctoral researcher Sandra Floyd and John Bowman, professor of plant biology at UC Davis.

The mechanism depends on microRNAs, short pieces of RNA that switch genes off by interfering with messenger RNAs that are produced when genes are read.

Floyd and Bowman looked at a family of genes found in all major groups of land plants called class III HD-Zip genes. They found that these genes are controlled by microRNAs and that the microRNA binding region is almost identical in moss, liverworts, club moss, ferns, Douglas fir, Mexican yew and Arabidopsis, a flowering plant often used in laboratory research.

Not only are the amino acid sequences of the proteins highly conserved, but also the nucleotide sequence of the microRNA binding site in the mRNA has been conserved for 400 million years, Bowman said.

This is the first demonstration of gene regulation by a microRNA in non-flowering plants such as mosses and ferns. A similarly ancient system of regulation by microRNAs has recently been found in animals, Floyd said.

The research is published in the April 1 issue of Nature.