A gene-switching mechanism dating back 400 million years to the first plants has been found by plant biologists at University of California Davis. The mechanism relies on microRNAs — parts of RNA that switch genes off by interceding messenger RNAs that are made when genes are read.
According to Andy Fell, at the UC Davis news service, "There were a number of researchers who were looking at how a series of commands in the genes tell a plant how to make a leaf or flower. There are different types of leaves, stems and structures. They were looking at how changes in those genes change the way a plant makes a different shape. It seems that the same basic switch is built into all different kinds of plants over a very wide range. Although the outcomes are very different, the mechanism to get there is basically the same."
According to UC Davis researcher Sandra Floyd and UC Davis plant biology professor John Bowman, a family of genes needed for stem and leaf development in flowering plants is controlled in the same way as other plants. Floyd and Bowman examined genes found in all major groups of land plants called class III homeodomain-leucine zipper (HD-Zip) genes. The microRNA binding region of the plants’ genes is almost identical to moss, liverworts, hornworts, club moss, ferns, Douglas fir, Mexican yew and Arabidopsis, a flowering plant used for research.
According to an April 1, 2004 article in Nature, microRNAs are an abundant class of RNAs that are thought to regulate the expression of protein-coding genes in plants. "HD-Zip genes in land plants are negatively regulated through a conserved microRNA mediated mechanism that has operated at least since the last common ancestor of bryophytes and seed plants."
According to Nature, the target sequence of two microRNAs, known to regulate genes in the class-III HD-Zip gene family of Arabidopsis, is "conserved in homologous sequences from all lineages of land plants, including bryophytes, lycopods, ferns and seed plants."
According to Bowman, the amino acid sequences of the proteins are highly conserved, and the nucleotide sequence of the microRNA-binding site has been conserved. "Our results indicate not only that microRNAs mediate gene regulation in non-flowering and flowering plants, but also that the regulation of this class of plant genes dates back more than 400 million years." This is the first example of gene regulation by a microRNA in non-flowering plants such as mosses and ferns.