[Na-Sheng Lin] Fibrillarin Methylates a Movement Protein to Help Satellite RNA Trafficking in Plants
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Fibrillarin (FIB) methylates P20 in the nucleolus, facilitating its association with satBaMV to form a ribonucleoprotein complex that traffics through plasmodesmata to neighboring cells, thereby promoting the systemic trafficking of satBaMV.
RNA trafficking is crucial in almost every phase of plant development. However, the mechanisms by which plant parasites—viruses—and even the parasites of viruses—satellite RNAs—move systemically within plants to establish infection remain poorly understood. Previously, we demonstrated that bamboo mosaic virus satellite RNA (satBaMV) traffics autonomously and systemically in a helper virus-independent but nucleolar protein (FIB)-dependent manner by forming a mobile ribonucleoprotein (RNP) complex comprising satBaMV, FIB, and satBaMV-encoded P20 movement protein. Here, we show that the arginine-rich motif (ARM) of P20 directs its nucleolar localization, enabling its interaction with FIB in the nucleolus and Cajal bodies, where FIB methylates the ARM. The methyltransferase (MTase) activity of FIB is indispensable for the systemic movement of satBaMV. Although FIB MTase-defective mutants retain their ability to bind satBaMV in vivo, they fail to complement long-distance satBaMV transport in FIBi plants. P20 methylation not only promotes its targeting to plasmodesmata (PD) but also triggers nucleocytoplasmic shuttling of FIB together with P20 as the RNP complex to PD. A satBaMV mutant harboring a non-methylated P20, but not a methylation-mimic P20, exhibited disrupted PD targeting and impaired P20-assisted satBaMV trafficking. Our findings provide mechanistic insights into how FIB-mediated P20 methylation positively regulates systemic trafficking of a subviral agent in plants. This research was led by Dr. Na-Sheng Lin at the Institute of Plant and Microbial Biology, Academia Sinica, in collaboration with Drs. Yau-Heiu Hsu and Chung-Chi Hu from the Graduate Institute of Biotechnology, National Chung Hsing University. Drs. Chih-Hao Chang and Jiun-Da Wang contributed equally as co-first authors. The research was funded by Academia Sinica Investigator Award and published in The Plant Cell (DOI: 10.1093/plcell/koaf224).
To highlight the significance of these findings, The Plant Cell produced an accessible “In Brief” entitled 「Hitching a ride: Bamboo mosaic virus satellite RNA hijacks the methyltransferase fibrillarin for a ride across the plant」, making the study understandable to a broader audience (https://doi.org/10.1093/plcell/koaf226).