Bishwas Sharma

Transposons drive genetic diversity and evolution by altering the genomic landscape over time. Here, we describe D ELAYED AB AXIAL TRICHOMES ( DAB ), a Helitron/RC transposable element in Arabidopsis thaliana that has a role in vegetative phase change and gametogenesis. A genome-wide association study (GWAS) for the timing of abaxial trichome development (an adult leaf trait) in A. thaliana revealed a conserved haplotype of polymorphisms within DAB that delays abaxial trichome production. CRISPR-Cas9-induced deletions of DAB are gametophytic pollen-lethal, indicating that this locus is also required for pollen production. DAB produces 24-nucleotide siRNAs with sequence complementarity to genes involved in embryogenesis, gametogenesis, and seed development. DAB also impacts the expression of ARGONAUTE genes, genes involved in RNA-directed DNA methylation (RdDM), as well as genes in several key genetic pathways. This global effect on gene expression suggests that DAB may have functions beyond those identified in this study.

Recently, post-transcriptional regulation of mRNA mediated by N⁶-methyladenosine (m⁶A) has been found to have profound effects on transcriptome regulation during plant responses to various abiotic stresses. However, whether this RNA modification can affect an oxidative stress response in plants has not been studied. To assess the role of m⁶A modifications during copper-induced oxidative stress responses, m⁶A-IP-seq was performed in Arabidopsis seedlings exposed to high levels of copper sulfate. This analysis revealed large-scale shifts in this modification on the transcripts most relevant for oxidative stress. This altered epitranscriptomic mark is known to influence transcript abundance and translation; therefore we scrutinized these possibilities. We found an increased abundance of copper-enriched m⁶A-containing transcripts. Similarly, we also found increased ribosome occupancy of copper-enriched m⁶A-containing transcripts, specifically those encoding proteins involved with stress responses relevant to oxidative stressors. Furthermore, the significance of the m⁶A epitranscriptome on plant oxidative stress tolerance was uncovered by assessing germination and seedling development of the mta (N⁶-methyladenosine RNA methyltransferase A mutant complemented with ABI3:MTA) mutant exposed to high copper treatment. These analyses suggested hypersensitivity of the mta mutant compared to the wild-type plants in response to copper-induced oxidative stress. Overall, our findings suggest an important role for m⁶A in the oxidative stress response of Arabidopsis.