Intrinsically disordered proteins SAID1/2 condensate on SERRATE for dual inhibition of miRNA biogenesis in Arabidopsis

Examination of genome-wide expression profiles of RNAs and small RNAs in three-week-old seedlings of Col-0 and said1/2-related mutants by high throughput sequencing. The intrinsically disordered proteins (IDPs) SAID1/2 act as negative regulators of SERRATE (SE), a core factor in miRNA biogenesis complex (microprocessor). SAID1/2 act to hijack pri-miRNAs from SE/ARS2 and inhibit microprocessor activity, whereas promoting phosphorylation and degradation of SE protein, leading to repression of production for a majority of miRNAs. These biochemical events likely take place in SAID1/2-SE condensates in vivo. This study not only deciphered the functions of poorly understood SAID gene family, but also uncovered a new regulatory layer of miRNA biogenesis in plants.