Fig. 8.

Schematic model of the evolution of plant Helitrons. We propose that the progenitor of plant Helitrons contained only a RepHel domain. Later, the PHRPA protein was introduced into the progenitor of mono- and dicotyledonous plants approximately 145 – 300 mya via horizontal transfer to form the first plant RPA-like Helitron. In the case of Mothra elements, the RepHel domain was later lost, thus introducing an additional level of “semi-autonomy” between the non-autonomous elements and the fully autonomous Helitrons