A new small RNA pathway has been described, in which microRNAs trigger the biogenesis of epigenetically activated small interfering RNAs (easiRNAs) from reactivated transposable elements in Arabidopsis thaliana. During reprogramming of the germ line, when epigenetic marks are erased and the plant genome is most vulnerable to activated transposons, these easiRNAs specifically target transposon transcripts. This plant transposon defense mechanism resembles the PIWI-interacting RNA pathway in animal germ lines, which also acts as a fail-safe mechanism to prevent transposon activation during reprogramming.