The production of micro RNAs from its precursors has already been extensively studied, especially in animal cells. "Micro RNAs in plants have evolved in parallel and independently. We had to assume that they could be processed in a different way," Pablo Manavella explains.
The scientists used a methodical trick to study the activity of micro RNAs in cells of thale cress plants. First, they developed a reporter system based on the bioluminescent protein luciferase from firefly; its DNA was integrated in the plant cells. Secondly, the scientists inserted in the plant genome a fragment of DNA containing a precursor of an artificial micro RNA that specifically inhibits luciferase. These plants thus initially showed no light emission despite containing the genes encoding luciferase. In a mass experiment, the scientists then triggered unspecific mutations in thousands of plants. With the aid of a special hypersensitive camera the few shining plants were sorted out. "In all these individuals some part of the micro RNA pathway must have been damaged so that luciferase was no longer silenced by the artificial micro RNA," says Pablo Manavella.
To identify the genes responsible for the failure in silencing luciferase, the scientists made use of a new technology developed at the Max Planck Institute, which enables the rapid detection of causal mutations by whole-genome sequence analysis. "Just a few years ago, this project would have been difficult to complete within two years. Nowadays, whole genome sequencing is a rapid and affordable method. By combining the screening test on luciferase activity with whole genome sequencing we could reduce the study period from years to several months," Pablo Manavella explains. Among the obtained mutants the scientists identified the phosphata
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