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-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, able to direct the synthesis of small RNAs responsible for desiccation tolerance. Transposition of CDT-1 retroelements have progressively increased the capacity of the species to synthesize small RNAs and thus recover after desiccation. 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.