Retrotransposons and the eternal leaves

The resurrection plant Craterostigma plantagineum can tolerate up to 96% loss of its relative water content and recover within hours after rehydration. In callus tissue desiccation tolerance is induced by pre-incubation with Abscisic acid (ABA). In callus and plant ABA treatment and dehydration induce a set of dehydration- and or ABA-responsive genes. T-DNA activation tagging led to the identification of CDT-1, a dehydration- and ABA-responsive gene which renders calli tolerant without ABA pre-incubation. Molecular analysis indicated that CDT-1 is a retroelement, present in multiple copy in the genome, and it directs the synthesis of small RNA responsible for desiccation tolerance. Via transposition, these retroelements have progressively increased the capacity of the species to synthesize small RNA and thus recover after dehydration. This may be a case of evolution towards the acquisition of a new trait, stimulated by the environment acting directly on intra-genomic DNA replication.