Extensive profiling of the expressions of tRNAs and tRNA-derived fragments (tRFs) reveals the complexities of tRNA and tRF populations in plants.

Evidence is emerging that tRNA-derived fragments (tRFs) are regulatory molecules. Studies of tRFs in plants have been based on conventional small RNA sequencing, and focused on profiling of tRF-5 and tRF-3 species. A more comprehensive and quantitative analysis of the entire tRF population is highly necessary. Here, we employ tRNA-seq and YAMAT-seq, and develop a bioinformatics tool to comprehensively profile the expressions of tRNAs and tRFs in plants. We show that in Arabidopsis, approximately half of tRNA genes are extremely weakly expressed, accounting for only 1% of total tRNA abundance, while ~12% of tRNA genes contribute to ~80% of tRNA abundance. Our tRNA sequencings in various plants reveal that tRNA expression profiles exhibit a cross-species conserved pattern. By characterizing the composition of a highly heterogeneous tRF population, we show that tRNA halves and previously unnoticed 10-16-nt tiny tRFs represent substantial portions. The highly accumulated 13-nt and 16-nt tiny tRFs in Arabidopsis indicate that tiny tRFs are not random tRNA degradation products. Finally, we provide a user-friendly database for displaying the dynamic spatiotemporal expressions of tRNAs and tRFs in the model plants Arabidopsis and rice.