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

Plants retain an exhaustive tRNA gene repertoire 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 tRNASer and tRNATyr genes (SYY cluster). They intersect with constitutive heterochromatin and are transcriptionally silenced. Here, we resolve the spatial expression pattern of this cluster along seedling establishment. We show the root cap columella and few adjacent lateral root cap cells to be the main sources of SYY cluster tRNAs. The transcriptional reactivation of this genomic region occurs there dispite of elevated DNA methylation levels. Furthermore, we evidence that these cells are able to accumulate high levels of a transgenic EXTENSIN rich in serine and tyrosine, and that the CRISPR/Cas9 deletion of the SYY cluster alters such phenomenon.