I. 阿拉伯芥與DNA甲基化相關基因之選殖與特性分析II. 鐵砲百合花藥與乾燥相關基因之選殖與特性分析

Abstract

DNA methylation is a conserved epigenetic mark that is critical for genome maintenance and development in plants and mammals. In plant, RNA-directed DNA methylation (RdDM) is an RNAi-based mechanism for establishing transcriptional gene silencing. From a genetic screen for second-site suppressors of the DNA demethylase mutant ros1, three new components (referred to as RDM2, RDM3 and RDM4) as well as seven known components (NRPD1, NRPE1, NRPD2a, AGO4, HEN1, DRD1, and HDA6) of the RdDM pathway were identified. One of novel RdDM components, RDM3 was chosen for further investigation. Loss-of-function mutations in RDM3 reduce DNA methylation and release the silencing of RdDM target loci without abolishing the siRNA triggers. RDM3 encodes a KTF protein with an N-terminal region similar to the transcription elongation factor SPT5 and a C-terminal region rich in GW/WG repeats. KTF1 colocalizes with ARGONAUTE 4 (AGO4) in punctate nuclear foci and binds AGO4 and RNA transcripts. Our results suggest KTF1 as an adaptor protein that binds scaffold transcripts generated by Pol V and recruits AGO4 and AGO4-bound siRNAs to form an RdDM effector complex. The dual interaction of an effector protein with AGO and small RNA target transcripts may be a general feature of RNA-silencing effector complexes.