UC Riverside

microRNAs (miRNAs) play regulatory roles in various developmental processes including stem cell maintenance and differentiation, which are central to animal and plant development. miRNAs function within a miRNA-protein complex termed RNA Induced Silencing Complex (RISC). In plants, miRNAs and the core protein component of RISC, argonaute proteins, have been shown to regulate the maintenance of stem cells. In Arabidopsis, the maintenance of floral stem cell fate is controlled both spatially and temporally. One aim of my Ph.D. thesis research was to uncover the mechanisms that underlie the programmed termination of floral stem cell maintenance. My studies show that miR165/166 and the argonaute protein that it associates with in vivo , AGO10, are both involved in the regulation of floral stem cells. This work is reported in Chapter I of the thesis. One intriguing observation made during my studies was that AGO10 represses the levels of miR165/166 in vivo, which is contrary to the expectation that argonaute proteins stabilize their associated miRNAs and implies the existence of a currently unknown mechanism regulating miRNA homeostasis. My research towards elucidating this regulatory mechanism is reported in Chapter II. Although the work has not been completed, I have accumulated evidence that AGO10 decreases the stability of miR165/166. Taken together, my thesis research has demonstrated that regulation of miRNA stability through a specialized argonaute protein is critical to the regulation of stem cells in plant development.