Transcriptional reactivation of the tRNASer/tRNATyr gene cluster in Arabidopsis thaliana root tip

Plants retain a repetitious tRNA gene content in their nuclear genome. How important are these individuals, how exactly plants orchestrate their usage, and for what purposes, is poorly understood. Arabidopsis thaliana chromosome 1 holds a cluster of tandemly repeated serine- and tyrosine-decoding tRNA genes (SYY cluster). They intersect with constitutive heterochromatin and are silenced in most parts of the plant. Yet, the natural conditions leading to their transcription remain unknown. Here, we resolve the tissular expression pattern of this cluster along seedling establishment. We show that the root cap columella and few adjacent lateral root cap cells are the main sources of SYY cluster tRNAs. The transcriptional reactivation of the SYY cluster occurs in these tissues although elevated DNA methylation levels. Furthermore, we evidence that these cells are able to accumulate high levels of a transgenic glycoprotein rich in serine, tyrosine, and proline, and that the CRISPR/Cas9 deletion of the SYY cluster alters the phenomenon. Altogether, our work sheds light on pioneering evidence of a developmental and cell-specific expression program for a plant tRNA gene. We provide new perspectives on the role of peculiar tRNA genes in conferring a potential for the high synthesis of glycoproteins in protective tissues of the meristem.