Functional Analysis Of OsNERD1 In Rice Epigenetic Regulation

RNA-directed DNA methylation (RdDM) is a transcriptional gene silencing (TGS) pathway existing widely in plants. DCL3, RDR2 and AGO4/6 are involved in RdDM and regulate the methylation of homology locus. A new pathway independent to RdDM is found recently in Arabidopsis, namely Needed for RDR2-independent DNA methylation (NERD) pathway. The key protein involved in the pathway is AtNERDl. AtNERD1 interacts with AGO2 and affect the methylation and histone modification of the newly arisen pseudogene and TEs by 21nt sRNAs. AtNERD1 plays an important role in DNA methylation variation and inheritance, and may affect the plant traits and adaptation to environments.The existence and conservation of NERD pathway in crops is still unknown. Rice is a monocoty crop widely cultivated which has more DNA elements than Arabidopsis. The study of OsNERD1 can expand the concepts of epigenetics and present the theoretical basis to rice breeding. The results in the article are displayed below:1. Sequence homology analysis suggests that rice has two proteins which are highly homologous to AtNERD1 named OsNERD1 and OsNERD2. OsNERD1 have the same domain as AtNERD1, especially the GW/WG repeats which is the key structure to direct the genomic DNA methylation in RdDM pathway via the interaction of AG04/SPT5L/NRPEA. The binding capacity to H3K4me3 was confirmed by in vitro binding assay. This capacity indicates that OsNERD1 involves in the epigenetic regulation in rice.2. A T-DNA insertion mutant was identified. AmiRNA method was used to obtain suppression materials and we found several transgenetic materials that the expression of OsNERD1 is lower than wt. At the same time, pollen sterility was observed in OsNERD1 mutants.3. In the OsNERD1 mutants, the expression of transposons were changed and some transposons are enriched in 21-nt sRNAs at the translation initiation region, indicating that OsNERD1 may be involved in the sRNAs directed DNA methylation. Further more, most of these diverse transposons belong to the Ty3/gypsy family which highly expressed in vegetative nucleus. The sterility of OsNERD1 may be caused by the highly expressed gypsy transposons family.