Transposable elements (TEs) are the main component of eukaryotic genomes. 
Besides their impact on genome size, TEs are also functionally important as they 
can alter gene expression and influence phenotypic variation. In plants, most 
top-down studies focus on extremely clear phenotypes such as the shape or the 
color of individuals and do not explore fully the role of TEs in evolution. 
Assessing the impact of TEs in a more systematic manner, however, requires 
identifying active TEs to further study their impact on phenotypes. In this 
chapter, we describe an in planta approach that consists in activating TEs by 
interfering with pathways involved in their silencing. It enables to directly 
investigate the functional impact of single TE families at low cost.