Origins of Life under Extreme Conditions: Compensatory Effect between Pressure and Temperature on RNA self-cleavage Activity
KADDOUR Hussein (1), VERGNE Jacques and MAUREL Marie-Christine (2)
Acides Nucléiques et Biophotonique, ANBioPhy FRE 3207 CNRS, UPMC Université Paris 06
1) hussein.kaddour@etu.upmc.fr &
2) marie-christine.maurel@upmc.fr

The discovery of hydrothermal vents in late seventies (1) greatly expands the possible range of sites for the origin of life. More recently, it was also reported that hydrothermal regions deep in the Earth's crust have surprisingly extensive microbial populations (2). Both hydrothermal vents and deep geothermal regions may have provided a refuge from giant impacts that sterilized the surface of the early Earth. This idea is supported by evidence from ribosomal RNA sequences which strongly suggests that the last common ancestor of all life on Earth was likely to have been a thermophilic microorganism (3,4). On the other hand, it was suggested that viroids and viroid-like satellite RNAs (which are small plant pathogenic RNAs) are plausible candidates as "living fossils" of a precellular RNA world (5), a genetic world where the first stage of life’s evolution had proceeded by RNA molecules performing the catalytic activities necessary to assemble themselves from a nucleotide soup (6). Taken together these ideas, we studied the self-cleavage activity of the Avocado Sunbloch Viroid under hydrostatic pressure in a range of 0.1 - 300 MPa and at temperatures ranging up to 80°C, including those conditions of the near hydrothermal vents which provide habitats for living cellular and viral species. The experiments were performed in an automated high pressure/temperature reactor which allows the removal of samples from the incubation chamber while the pressure is maintained constant (7). Our results show that pressure decreases the RNA activity while temperature increases it. These results underscore a compensatory effect between temperature and pressure, which could have favored some primitive reactions under conditions of early life and then, could have facilitated adaptation to these hydrothermal niches where rich chemistry, high temperature and high pressure offer a plausible nest for the emergence of life (8).

References :
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