Scientists develop new tool for rice breeders

EU-funded researchers have developed a genetic tool which allows rice breeders to block the action of genes which confer unwanted traits, the discovery promises to radically speed up the
transfer of genes between varieties.

Rice (Oryza sativa) is one of the world’s most important crops: it forms the basis of the diet for around half the world’s population, and is grown in 89 countries on six continents. Currently,
when a plant with a new, desirable trait is identified, it takes breeders years to transfer the gene to other varieties without affecting all the other genes which the target variety needs in
order to thrive in its local environment.

Now scientists from Germany’s Max Planck Institute for Developmental Biology and the International Rice Research Institute in the Philippines have developed a tool which means that in the
future, the process of transferring genes from one variety to another could take weeks, instead of years. Their results are published in the journal PLoS ONE.

The technique involves using tiny molecules of RNA called microRNAs to switch off certain genes. Although this sounds counterintuitive, in fact many desirable traits in rice are the result of
inactivated genes. For example, rice’s ‘green revolution’ resulted from the loss of a gene that normally made the rice plants very tall (and hence prone to toppling over under the weight of too
many heavy rice grains).

MicroRNAs are found naturally in plants and animals, where they have an important role in regulating gene activity. By interfering in the gene activity process, microRNAs effectively block the
activity of certain genes.

In this latest study, the scientists used artifical miRNAs (amiRNAs) to access this gene silencing pathway and switch off specific genes. With this method, they succeeded in switching off a
gene called Eui1 in two strains of rice. When Eui1 is inactive, the plant’s flowers tend to be fertilised by pollen from other plants instead of being self-fertilised. Cross-pollination is
important to breeders because it enables them to produce hybrid seeds.

The Eui1 mutation first arose in a japonica rice variety, and after years of breeding, rice researchers succeeded in introducing it into indica varieties. In this study, the researchers used
artificial miRNA to switch off the Eui1 gene in two different rice varieties, including the indica variety IR64, the most commonly grown strain in South-East Asia. Within weeks, they had
successfully silenced the Eui1 gene in these other strains.

‘As well as allowing the quick transfer of reduced gene function to different varieties and even species, artificial microRNAs also speed up the identification of important genes and the
discovery of new gene functions,’ commented Norman Warthmann of the Max Planck Institute for Developmental Biology. Currently, the function of most rice genes remains a mystery.

‘MicroRNAs have been found in all plant species examined so far,’ added Detlef Weigel, also of the Max Planck Institute. ‘It should therefore be possible to adapt this technique for other
crops, thereby opening up new avenues to enhance the nutritional value and agronomic performance of plants.’

EU support for the work came from the EU-funded SIROCCO (‘Silencing RNAs: organisers and coordinators of complexity in eukaryotic organisms’) project, which is financed through the ‘Life
sciences, genomics and biotechnology for health’ thematic area of the Sixth Framework Programme (FP6).

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