Theses and Dissertations
Mississippi State University
Date of Degree
Dissertation - Open Access
Doctor of Philosophy (Ph.D)
College of Arts and Sciences
Department of Biological Sciences
RNAs play essential roles in various biological processes. Mounting evidence has demonstrated that RNA subcellular localization and intercellular trafficking govern their functions in coordinating plant growth at the organismal level. Beyond that, plants constantly encounter foreign RNAs (i.e., RNAs from pathogens including viruses and viroids). The subcellular localizations of RNAs are crucial for their function. While numerous types of RNAs (i.e., mRNAs, small RNAs, rRNAs, tRNAs, and long noncoding RNAs) have been found to traffic in a non-cell-autonomous fashion within plants, the underlying regulatory mechanism remains unclear. Viroids are single-stranded circular noncoding RNAs, which entirely rely on their RNA motifs to exploit cellular machinery for organelle entry and exit, cell-to-cell movement through plasmodesmata, and systemic trafficking. Viroids represent an excellent model to dissect the role of RNA 3-dimensional (3D) structural motifs in regulating RNA movement. Using nuclear-replicating viroids as a model, we showed that cellular Importin alpha-4 is likely involved in viroid RNA nuclear import, empirically supporting the involvement of Importin-based cellular pathway in RNA nuclear import. We also confirmed the involvement of a cellular protein (Virp1) that binds both Importin alpha-4 and viroids. Moreover, a conserved C-loop in nuclear-replicating viroids serves as a key signal for nuclear import. Disrupting C-loop impairs Virp1 binding, viroid nuclear accumulation and infectivity. Further, C-loop exists in a subviral satellite noncoding RNA that relies on Virp1 for nuclear import.
On the other hand, no viroid can systemically infect the model plant Arabidopsis thaliana, suggesting the existence of non-host resistance yet to be understood. Here, we attempted to test whether a gene involved in RNA silencing, RNA-dependent RNA polymerase 6 (RDR6), plays a role in non-host resistance in Arabidopsis. I will discuss the data below in detail.
Ma, Junfei, "The emerging value of the viroid model in understanding plant responses to foreign RNAs" (2022). Theses and Dissertations. 5709.
Biology Commons, Plant Biology Commons, Plant Pathology Commons