Ikuko Hara-Nishimura

Transposable elements (TEs) contribute to plant evolution, development, and adaptation to environmental changes, but the regulatory mechanisms are largely unknown. RNA-directed DNA methylation (RdDM) is 1 TE regulatory mechanism in plants. Here, we identified that novel ARGONAUTE 1 (AGO1)-binding Tudor domain proteins Precocious dissociation of sisters C/E (PDS5C/E) are involved in 24-nt siRNA production to establish RdDM on TEs in Arabidopsis thaliana. PDS5 family proteins are subunits of the eukaryote-conserved cohesin complex. However, the double mutant lacking angiosperm-specific subfamily PDS5C and PDS5E (pds5c/e) exhibited different developmental phenotypes and transcriptome compared with those of the double mutant lacking eukaryote-conserved subfamily PDS5A and PDS5B (pds5a/b), suggesting that the angiosperm-specific PDS5C/E subfamily has a unique function in angiosperm plants. Proteome and imaging analyses revealed that PDS5C/E interact with AGO1. The pds5c/e double mutant had defects in 24-nt siRNA accumulation and CHH DNA methylation on TEs. In addition, some lncRNAs that accumulated in the pds5c/e mutant were targeted by AGO1-loading 21-nt miRNAs and 21-nt siRNAs. These results indicate that PDS5C/E and AGO1 participate in 24-nt siRNA production for RdDM in the cytoplasm. These findings indicate that angiosperm plants evolved a new regulator, the PDS5C/E subfamily, to control the increase in TEs during angiosperm evolution.