Pluripotent stem cells localized in proliferating growth centers, the meristems, are the origin of life-long organ formation and growth in higher plants. In the shoot apical meristem of Arabidopsis thaliana, the close...Pluripotent stem cells localized in proliferating growth centers, the meristems, are the origin of life-long organ formation and growth in higher plants. In the shoot apical meristem of Arabidopsis thaliana, the closelyrelated ARGONAUTE proteins AGO1 and ZLL/AGO10 bind miR165/166 species to regulate mRNAs of HDZIP III transcription factors that are essential to maintaining stem cells. Several genetic studies showed thatAGO1 and ZLL/AGO10 act redundantly to maintain stem cells. By contrast, the reported biochemical datasuggested antagonistic functions: AGO1 utilizes miR165/166 to slice HD-ZIP III mRNAs, whereas ZLL/AGO10 promotes degradation of miR165/166 and thus stabilizes HD-ZIP III mRNAs. How these differentfunctions are balanced in stem cell regulation has remained enigmatic. Here, we show that autorepressionof AGO1 through miR168-mediated slicing of its own RNA is required to maintain the ability of AGO1 to suppress HD-ZIP III mRNAs. Increased AGO1 expression, either in the miR168a-2 mutant or by transgenicexpression, inhibits this ability despite the presence of high levels of miR165/166, effectively uncouplingHD-ZIP III and miR165/166 expression. AGO1 activity can be restored, however, by increasing the levelsof chaperones SQN and HSP90, which promote assembly of RNA-induced silencing complex (RISC). Thissuggests that cellular abundance of SQN and HSP chaperones limits AGO1-mediated RNA interferencein shoot meristem stem cell regulation. Localized misexpression of AGO1 indicates that the cells surrounding the shoot meristem primordium play a crucial role in stem cell development. Taken together, our studyprovides a framework that reconciles biochemical and genetic data, showing that restriction of AGO1 levelsby miR168-mediated autorepression is key to RISC homeostasis and the function of AGO1 in stem cellregulation.展开更多
基金This work was funded by grants from the Baden-Wurttemberg Stiftung and by the German Research Foundation(DFG)under Germany’s Excellence Strategy(CIBSS-EXC-2189-Project ID390939984)by grants(La606/14,La606/17,ERA-CAPS,to T.L.)and a stipend from the China Scholarship Council to F.D.
文摘Pluripotent stem cells localized in proliferating growth centers, the meristems, are the origin of life-long organ formation and growth in higher plants. In the shoot apical meristem of Arabidopsis thaliana, the closelyrelated ARGONAUTE proteins AGO1 and ZLL/AGO10 bind miR165/166 species to regulate mRNAs of HDZIP III transcription factors that are essential to maintaining stem cells. Several genetic studies showed thatAGO1 and ZLL/AGO10 act redundantly to maintain stem cells. By contrast, the reported biochemical datasuggested antagonistic functions: AGO1 utilizes miR165/166 to slice HD-ZIP III mRNAs, whereas ZLL/AGO10 promotes degradation of miR165/166 and thus stabilizes HD-ZIP III mRNAs. How these differentfunctions are balanced in stem cell regulation has remained enigmatic. Here, we show that autorepressionof AGO1 through miR168-mediated slicing of its own RNA is required to maintain the ability of AGO1 to suppress HD-ZIP III mRNAs. Increased AGO1 expression, either in the miR168a-2 mutant or by transgenicexpression, inhibits this ability despite the presence of high levels of miR165/166, effectively uncouplingHD-ZIP III and miR165/166 expression. AGO1 activity can be restored, however, by increasing the levelsof chaperones SQN and HSP90, which promote assembly of RNA-induced silencing complex (RISC). Thissuggests that cellular abundance of SQN and HSP chaperones limits AGO1-mediated RNA interferencein shoot meristem stem cell regulation. Localized misexpression of AGO1 indicates that the cells surrounding the shoot meristem primordium play a crucial role in stem cell development. Taken together, our studyprovides a framework that reconciles biochemical and genetic data, showing that restriction of AGO1 levelsby miR168-mediated autorepression is key to RISC homeostasis and the function of AGO1 in stem cellregulation.
