Abundance of tRNA-derived small RNAs in phosphate-starved Arabidopsis roots.

Several research advances have indicated an important role of transfer RNA (tRNA)-derived small RNAs in modulating developmental processes or stress responses. Recently, from the deep sequencing of small RNAs in Arabidopsis (Arabidopsis thaliana), we identified a new class of 19-nucleotide (nt) small RNAs corresponding to the 5' end of tRNA accumulated at high levels in phosphate-starved roots. In two very recent studies, 19-nt tRNA fragments were also observed in human cells, suggesting their widespread nature. In our study, tRNA halves cleaved at the anticodon loop, the most common tRNA fragments found, were predominant in roots. These results showed a spatial and temporal expression pattern of small RNAs derived from specific cleavage of tRNA molecules. Although the function of these tRNA-derived small RNAs under phosphate deficiency remains unknown, their diversity, biogenesis and potential function are henceforth summarized and discussed. Certainly, they will emerge as a novel class of regulatory small RNAs.