Transposons are mobile DNA sequences that influence genome evolution, but that can also cause deleterious mutations when they insert into genes. A team at the IBMP led by Todd Blevins has discovered the mechanism that plants use to assemble RNA polymerase IV (Pol IV) to target and repress transposons.
Published in Nature Communications, this work is a collaboration with Julie Law’s team at the Salk Institute (USA), Florent Waltz at the University of Basel (Switzerland) and the Proteomics Platform Strasbourg-Esplanade. The authors identified a novel structure in Pol IV that allows it to dock with chromatin remodeler-like factors, called CLSY proteins, which target Pol IV to transposons, where it produces small RNAs that guide the silencing of mobile DNA. Over evolutionary history Pol IV has also begun to control the expression of genes in close proximity to transposons. As a consequence, CLSY-Pol IV docking plays roles both in gene regulation and in maintaining genome stability.
The CLSY proteins have diversified in flowering plants like Arabidopsis thaliana, which uses four different CLSYs (CLSY1,2,3,4) to recruit Pol IV to thousands of sites in the genome. The authors showed that each Pol IV enzyme docks with at most one type of CLSY, leading them to propose a “one CLSY per Pol IV” model for transposon silencing. These findings provide structural and functional insights into the mechanism that distinguishes Pol IV from all other RNA polymerases. This work has implications not only for understanding the processes of genetic regulation in plants, but also for potential applications in crop improvement and resilience to environmental stresses.
