Genome-wide analysis of mRNA decay in Arabidopsis shoot and root reveals the importance of co-translational mRNA decay in the general mRNA turnover.

Until recently, the general 5'-3' mRNA decay was placed in the cytosol after the mRNA was released from ribosomes. However, the discovery of an additional 5' to 3' pathway, the Co-Translational mRNA Decay (CTRD), changed this paradigm. Up to date, defining the real contribution of CTRD in the general mRNA turnover has been hardly possible as the enzyme involved in this pathway is also involved in cytosolic decay. Here we overcame this obstacle and created an Arabidopsis line specifically impaired for CTRD called XRN4ΔCTRD. Through a genome-wide analysis of mRNA decay rate in shoot and root, we tested the importance of CTRD in mRNA turnover. First, we observed that mRNAs tend to be more stable in root than in shoot. Next, using XRN4ΔCTRD line, we demonstrated that CTRD is a major determinant in mRNA turnover. In shoot, the absence of CTRD leads to the stabilization of thousands of transcripts while in root its absence is highly compensated resulting in faster decay rates. We demonstrated that this faster decay rate is partially due to the XRN4-dependent cytosolic decay. Finally, we correlated this organ-specific effect with XRN4ΔCTRD line phenotypes revealing a crucial role of CTRD in mRNA homeostasis and proper organ development.