Determination of genes involved in the microRNA turnover in Arabidopsis thaliana

Louis, Firas (2023) Determination of genes involved in the microRNA turnover in Arabidopsis thaliana. Doctoral thesis, University of East Anglia.

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microRNAs are short 21-24nt small RNAs responsible of the regulation of proteins level in both plants and animals and as crucial regulators, they need to be tightly regulated. In plants, miRNAs are transcribed from a MIR gene and form a long transcript with a stem-loop structure necessary for processing into a smaller dsRNA by the Dicing body. The duplex is then methylated by HEN1 that confers protection against 3’ nucleases. One of the two strands is loaded into its partner, an ARGONAUTE protein to form the RISC complex that degrades complementary mRNAs. miRNAs can then be truncated by SDN1 or urydilated by HESO1 and/or URT1 to promote their degradation. However, SDN1 cannot degrade urydilated miRNAs and the protein responsible is still unknow. During my PhD, I tried to uncover this protein by a screening assay using a GFP transgene targeted by miR395 in low sulphur conditions and by rescuing the hen1 background with different candidate genes predicted to interact with HESO1. While the screening assay did not produce sufficient results and needs some improvements, the other approach led us to a small phenotypic rescue of the hen1 background by sua, which is a splicing factor, despite not having a miRNA level increase in the vegetative stage. The alternative splicing analysis between sua and the wild type (Col-0) highlighted an unknown nuclease (namely RNase X). The mutant shows a higher level of some miRNAs, an increased tailing and has a better fitness compared to Col-0, indicative of the importance of this gene. While more needs to be uncovered on this RNase X, the results suggest that it regulates a subset of miRNAs and that it may be involved in the degradation of a subset of U-tailed miRNAs.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Chris White
Date Deposited: 12 Jun 2024 10:01
Last Modified: 12 Jun 2024 13:02

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