A new method to identify global targets of RNA-binding proteins in plants

Background RNA-binding proteins (RBPs) play crucial roles in various aspects of post-transcriptional gene expression; their functions can vary between tissues, cell types, developmental stages, and environmental conditions. Identifying RBP target RNAs and investigating whether they are differentially bound by RBPs in different cell types, stages, or conditions could shed light on RBP functions. Although several strategies have been designed to identify RBP targets, they involve complicated biochemical steps and require large quantities of material, and only a few studies using these techniques have been performed in plants. The TRIBE (targets of RNA binding proteins identified by editing) method was recently developed to identify RBP targets using a RBP coupled to the catalytic domain of a Drosophila RNA editing enzyme and expressing this fusion protein in vivo . The resulting novel editing events can be identified by sequencing. This technique uses little material and does not require complex biochemical steps, however it is not yet adapted for use in plants. Results We successfully applied an optimized genome-wide TRIBE method in plants. We selected the splicing regulator polypyrimidine tract-binding protein (PTB) as a model protein for testing the TRIBE system in the moss Physcomitrium patens . We demonstrated that 13.81% of protein-coding gene transcripts in P. patens are targets of PTB. Most potential PTB binding sites are located in coding sequences and 3’ untranslated regions, suggesting that PTB performs multiple functions besides pre-mRNA splicing in this moss. In addition, TRIBE showed reproducible results compared to other methods. Conclusions We have developed an alternative method based on the TRIBE system to identify RBP targets in plants globally, and we provide guidance here for its application in plants.