SERRATE is required for intron suppression of RNA silencing in Arabidopsis

Transposons and viruses are generally devoid of introns and are prime targets for small interfering RNAs (siRNAs) and RNA silencing. Conversely, endogenous genes often contain introns and are not usually subjected to post-transcriptional gene silencing by siRNAs. In a recent study, we reported that efficient intron splicing directly suppresses siRNA biogenesis and RNA silencing of a Green Fluorescence Protein (GFP) transgene. Splicing-mediated suppression of GFP silencing was dependent on ABH1, the Arabidopsis ortholog of human mRNA cap-binding protein 80. Furthermore, genome-wide analyses of Arabidopsis small RNA libraries showed that exons from intron-containing genes accumulate less small RNAs than exons from intronless genes. Our in silico analysis therefore suggested that intron splicing has a fundamental role in protecting endogenous genes from becoming templates for siRNA biogenesis and RNA silencing. Here, we show that SERRATE (SE) is also required for splicing-mediated suppression of RNA silencing in Arabidopsis. SE encodes a zinc finger protein that, like ABH1, functions in micro-RNA (miRNA) biogenesis and intron splicing. The implications of our findings are also discussed in a broader context.