Parallel Relaxation of Stringent RNA Recognition in Plant and Mammalian L1 Retrotransposons

Abstract

L1 elements are mammalian non–long terminal repeat retrotransposons, or long interspersed elements (LINEs), that significantly influence the dynamics and fluidity of the genome. A series of observations suggest that plant L1-clade LINEs, just as mammalian L1s, mobilize both short interspersed elements (SINEs) and certain messenger RNA by recognizing the 3′-poly(A) tail of RNA. However, one L1 lineage in monocots was shown to possess a conserved 3′-end sequence with a solid RNA structure also observed in maize and sorghum SINEs. This strongly suggests that plant LINEs require a particular 3′-end sequence during initiation of reverse transcription. As one L1-clade LINE was also found to share the 3′-end sequence with a SINE in a green algal genome, I propose that the ancestral L1-clade LINE in the common ancestor of green plants may have recognized the specific RNA template, with stringent recognition then becoming relaxed during the course of plant evolution.