Transcriptional reactivation of the tRNA^Ser/tRNA^Tyrgene cluster inArabidopsis thalianaroot tip

ABSTRACT 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 tRNA Ser and tRNA Tyr genes (SYY cluster). They intersect with constitutive heterochromatin and are transcriptionally silenced. Here, we resolve the tissular 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 although 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. Altogether, our work sheds light on pioneering evidence of a developmental and cell-specific expression program for a plant tRNA gene.