Mechanism of Small RNA Movement
Higher plants rely on the movement of signals between cells to coordinate gene expression, to define cell type and polarity during development, to respond to environmental stimuli, and for defence against pathogen infection. These signals can take a variety of forms, from simple molecules diffusing between symplastically-linked cells, to actively transported protein complexes.
Small regulatory RNAs (sRNAs) are able to regulate gene expression through sequence-specific interactions and recruitment of protein complexes to degrade mRNA, block translation or modify chromatin to inhibit transcription. Intense study of sRNAs since their first description has revealed that developmental decisions depend on expression of sRNA in strictly defined physical and temporal patterns. Recently, sRNAs have also been shown to move both locally (cell-to-cell) and systemically in plants. These mobile sRNAs perform essential and specific regulatory roles in cells at a distance from their source of biogenesis.
Here, we examine both short-distance (cell-to-cell) and long-distance (systemic) sRNA signalling in plants. We outline the known requirements for sRNA biogenesis and activity, and discuss the roles of sRNAs in gene regulation. Additionally, we present examples of sRNAs that have been shown to move cell-to-cell to influence development of the recipient tissue. We also discuss several experimental systems that have been used to define the requirements for cell-to-cell and systemic movement of sRNA signals. Finally, we highlight some crucial gaps in our knowledge regarding mechanism of intercellular movement of sRNAs in plants.
KeywordsTranscriptional Gene Silence Vegetative Nucleus Leaf Primordium Silence Signal Secondary siRNAs
The authors thank Dr. Uwe Dressel and Dr Iain Searle for comments on the manuscript. The authors are also grateful for research support from the Australian Research Council to BJC, and a Grains Research and Development Corporation scholarship to NRG.
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