Date of Award

6-2016

Degree Name

Master of Science

Department

Biological Sciences

First Advisor

Dr. Yan Lu

Second Advisor

Dr. Todd J. Barkman

Third Advisor

Dr. Pamela Hoppe

Access Setting

Masters Thesis-Campus Only

Restricted to Campus until

6-15-2026

Abstract

RNA editing is a conserved mechanism of post-transcriptional modification in eukaryotes that changes specific nucleotides in RNA transcripts. In flowering plants, this is limited to cytidine to uridine deaminations. Plastid RNA editing events are critical for plastid development and the loss of editing can result in untranslated or non-functional proteins. There have been 40 RNA editing events discovered in the Arabidopsis thaliana plastid. Recently organellar RNA recognition motif (ORRM) proteins have been shown to broadly affect plastid RNA editing and interact with sequence specific trans-factor pentatricopeptide repeat proteins (PPR). ORRM proteins contain a canonical RNA recognition motif that has been shown to specifically bind the transcripts of affected RNA editing events. In this study, we characterized a novel ORRM protein, named ORRM6. The orrm6 mutants showed retarded growth, reduced total chlorophyll content, and decreased accumulation of Photosystem II (PSII) proteins. We discovered that loss-of-function mutations in the ORRM6 gene severely affect two editing events: psbF-77 and accD-794. In orrm6 mutants, editing at the psbF-77 site is almost completely abolished and editing at the accD-794 site is reduced by 55%. Electrophoretic shift assays showed that recombinant ORRM6 binds with slightly higher affinity towards accD and psbF transcripts than psbE. ORRM6 is distinct from other ORRMs, because it only affects two editing events in the plastid. These data add another layer of complexity to the increasingly complex editosome.

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