Retrotransposons and siRNA have a role in the evolution of desiccation tolerance leading to resurrection of the plant Craterostigma plantagineum

• Craterostigma plantagineum can lose up to 96% of its water content but fullyrecover within hours after rehydration. The callus tissue of the plant becomesdesiccation tolerant upon pre-incubation with abscisic acid (ABA). In callus andvegetative organs, ABA addition and water depletion induce a set of dehydrationresponsivegenes.• Previously, activation tagging led to the isolation of Craterostigma desiccationtolerant (CDT-1), a dehydration-related ABA-inducible gene which renders callusdesiccation tolerant without ABA pre-treatment. This gene belongs to a family ofretroelements, members of which are inducible by dehydration.• Craterostigma plantagineum transformation with mutated versions of CDT-1indicated that protein is not required for the induction of callus desiccation tolerance.Northern analysis and protoplast transfection indicated that CDT-1 directs thesynthesis of a double-stranded 21-bp short interfering RNA (siRNA), which opensthe metabolic pathway for desiccation tolerance.• Via transposition, these retroelements have progressively increased the capacity ofthe species to synthesize siRNA and thus recover after dehydration. This may be a caseof evolution towards the acquisition of a new trait, stimulated by the environmentacting directly on intra-genomic DNA replication