Mau, M., Corral, J. M., Vogel, H., Melzer, M., Fuchs, J., Kuhlmann, M., et al. (2013). The conserved chimeric transcript UPGRADE-2 is associated with unreduced pollen formation and is exclusively found in apomictic Boechera species. Plant Physiology, 163(4), 1640-1659. doi:10.1104/pp.113.222448.