The <i>DELAYED ABAXIAL TRICHOMES</i> Helitron has dual functions in vegetative and pollen development in <i>Arabidopsis thaliana</i>

Transposons drive genetic diversity and evolution by altering the genomic landscape over time. Here, we describe <i>D</i><i>ELAYED</i> <i>AB</i><i>AXIAL TRICHOMES</i> (<i>DAB</i>), a Helitron/RC transposable element in <i>Arabidopsis thaliana</i> 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 <i>A. thaliana</i> revealed a conserved haplotype of polymorphisms within <i>DAB</i> that delays abaxial trichome production. CRISPR-Cas9-induced deletions of <i>DAB</i> are gametophytic pollen-lethal, indicating that this locus is also required for pollen production. <i>DAB</i> produces 24-nucleotide siRNAs with sequence complementarity to genes involved in embryogenesis, gametogenesis, and seed development. <i>DAB</i> also impacts the expression of <i>ARGONAUTE</i> 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 <i>DAB</i> may have functions beyond those identified in this study.