Researchers at the Max Planck Institute (MPI) for Developmental Biology in Tübingen, Germany, together with colleagues at the International Rice Research Institute in the Philippines, this week published their findings on a new technique that could speed up gene silencing in rice breeding.
In some cases, the inactivation of a particular gene could result in an improved quality crop. Gene silencing is considered to be an important mechanism by crop breeders, as it allows for the inactivation of certain genes without the need for lengthy breeding and cross-breeding to achieve gene transfer.
The new study published in PLoS ONE this week, details a specific gene silencing technique using artificial miRNAs in rice (Oryza sativa). The researchers explain that MicroRNAs are 20-22 bp long RNA molecules with important functions in regulating gene activity both in animals and plants.
In plants, MicroRNAs cause highly specific degradation of sequence-matched messenger RNAs, which encode enzymes, regulatory factors or other proteins. The end effect is that the corresponding gene is silenced, said the researchers, led by Norman Warthmann.
"With artificial miRNAs (amiRNAs), this natural silencing pathway can be harnessed to inactivate genes of interest to the breeder, with unprecedented specificity," they said.
"MiRNAs have been found in all plant species examined so far. It should hence be possible to adapt the technique of gene silencing by artificial miRNAs to other crops and it may provide an important new avenue to enhance agronomic performance and nutritional value."
The gene silencing method used for this study had been initially pioneered in the model plant Arabidopsis thaliana by Detlef Weigel's research group at the Max Planck Institute in Tübingen, before the scientists decided to also apply it to rice.
One of the rice genes they targeted was Eui1. Deactivating this gene allows for the top part of the rice plant to grow taller and more easily fertilize neighbouring plants. According to Warthmann and his team, breeders use this genetic method for hybrid seed production.
The researchers explain that the Eui1 mutation was originally identified as a spontaneous mutant in a japonica rice variety. It was introduced into indica varieties by several years of breeding.
However, by using an artificial miRNA targeting the Eui1 messenger RNA, the researchers at the International Rice Research Institute said that within weeks they were able to obtain plants with the desired property in two different rice varieties. One of the varieties was indica variety IR64, the most commonly grown strain in South-East Asia.
Warthmann and his team also reported successful silencing of two other genes, Pds and SPl11.
"Besides allowing the quick transfer of reduced gene function between different varieties, artificial miRNAs also accelerate the initial identification of important genes and the discovery of functions of genes that have not been studied before. Potential applications in rice breeding are manifold and they don't stop at rice genes," they said.
"By targeting pathogen-derived genes, for example, it should be possible to enhance virus and insect resistance. In addition, because they act dominantly, they are also perfectly suited for hybrid breeding."
Source: Highly Specific Gene Silencing by Artificial miRNAs in Rice. (2008) PLoS ONE 3(3): e1829. doi:10.1371/journal.pone.0001829
Authors: Warthmann N, Chen H, Ossowski S, Weigel D, Hervé P