Abstract
Mutations in ZIPPY(ZIP)/AGO7, RDR6, SGS3 and DCL4, accelerate juvenile-to-adult transition in Arabidopsis. By molecular genetic analysis of these mutants we found a novel class of endogenous siRNAs termed trans-acting siRNAs (ta-siRNAs), and showed a pathway for the biogenesis of them. Because ZIP is not required for production of ta-siRNAs from TAS1 and TAS2, how ta-siRNAs cause the phenotype of zip was unknown. However, it was shown that the ta-siRNA generated from TAS3 (ta-siARF) targets ETT/ARF3 and ARF4 of the auxin response factor family of transcription factors. Our results showed ta-siARF is absent in zip, rdr6 and sgs3, and ETT/ARF3 and ARF4 transcripts are upregulated. On the other hand, our genetic approach identified ETT/ARF3 and ARF4 mutants as suppressors of zip. Taken together, the abnormality of juvenile-to-adult transition in the mutants is attributed to the absence of ta-siARF.
