Evolution towards increasing complexity through functional diversification in a protocell model of the RNA world

The encapsulation of genetic material inside compartments together with
the creation and sustenance of functionally diverse internal components
are likely to have been key steps in the formation of ’live’, replicating
protocells in an RNA world. Several experiments have shown that RNA
encapsulated inside lipid vesicles can lead to vesicular growth and
division through physical processes alone. Replication of RNA inside such
vesicles can produce a large number of RNA strands. Yet, the impact of
such replication processes on the emergence of the first ribozymes inside
such protocells and on the subsequent evolution of the protocell
population remains an open question. In this paper, we present a model for
the evolution of protocells with functionally diverse ribozymes. Distinct
ribozymes can be created with small probabilities during the error-prone
RNA replication process via the rolling circle mechanism. We identify the
conditions that can synergistically enhance the number of different
ribozymes inside a protocell and allow functionally diverse protocells
containing multiple ribozymes to dominate the population. Our work
demonstrates the existence of an effective pathway towards increasing
complexity of protocells that might have eventually led to the origin of
life in an RNA world.