New Function Of AGO1 In Arabidopsis Small RNA Pathway

RNA silencing is an essential way of gene regulation in organisms,and it exists in various periods of growth and development of organisms.AGO1 protein is the crucial effector of RNA silencing pathway and an important regulator of post-transcriptional gene silencing(PTGs)in plants.At present,the functional study of AGO1 is mainly focused on the conserved domain with the regular three-dimensional structure,and there is seldom research on the N-terminal coil structure which does not exhibit a fine spatial structure.In this study,the point mutant of the N-terminal coil,ago1-38 was used to identify some novel functions of AGO1 in small RNA pathway.In this study,the in-depth analysis was carried out by methods of plant epigenetics,molecular biology and bioinformatics.It was found that the plant phenotype of ago1-38 was very special,and there was a cluster of small abnormal compound leaves growing at the back of petiole,and the leaves were bent more than 90 degrees at this point,and the leaves curled irregularly.Due to its special mutation site and plant phenotype,ago1-38 could be taken as a good example for the detection of new function of AGO1.By small RNAseq analyses,it was found that ago1-38 has a bunch of down-regulated 24 nt DSRs,and these down-regulated 24 nt DSRs mostly belong to the P4_siRNA type of the RdDM pathway,they are derived from the Pol IV-RDR2-DCL3 pathway and may bind to AGO4/6 to affect genomic methylation.Furthermore,it was found by mRNA-seq analyses that RDR1 and NRPE1 were up-regulated in ago1-38.According to further molecular phenotype and the double mutant phenotypic analysis,it was found that overexpression of RDR1 led to the plant phenotype of ago1-38 and the decrease of 24 nt DSRs.Interestingly,we found that the expression of JA/SA pathway-associated genes in ago1-38 were elevated,and these JA/SA pathway-associated genes was reported to promote RDR1 expression.We proposed a model that the high level of RDR1 competed with RDR2 then resulted in the reduction of 24 nt DSRs.In summary,we take the advantage of a specific site of AGO1 mutant to reveal an association between AGO1 and 24 nt siRNA production,it was widely accepted that AGO1 was mainly associate with 21 and 22 nt small RNAs.Our study provides a new aspect of AGO1 in the epigenetics pathway.