Genetic requirements for generation of the 24-nt hc-siRNA415. (A) Analysis of mutants impaired in small RNA biogenesis, dcl and rdr mutants. The same blot was successively hybridized, stripped, and re-hybridized to oligonucleotide probes corresponding to the complementary sequence of the indicated small RNAs. RNA blots were also probed with the U6 probe for loading control. (B) Analysis of ago4, nrpd2 (common to Pol IV and Pol V) and nrpe1 (Pol V) mutants. (C) Small RNA blot analysis of the hc-siRNA415 in different plant species.