UC Irvine

RNA editing in plants converts cytidines to uridines (C-to-U) in chloroplast and

mitochondrial transcripts. Pentatricopeptide repeat (PPR) protein family members have

been shown to be required for editing, and possess key characteristics of editing

deaminases found in other organisms. PPRs have an N-terminal RNA binding domain

responsible for RNA recognition and a C-terminal DYW domain that has deaminase-like

characteristics.

The role of several features of the DYW domain was investigated. The DYW domain

includes the HXE motif that provides a glutamate residue that is catalytically required.

Glutamate to alanine substitution ablated editing, and establishes a key characteristic of

the DYW domain that is required for editing. In addition, a highly conserved PG box was

identified between the N- and C-terminal domains that was required for editing in PPRs

that lacked a DYW domain, and the PG box may be required for protein-protein

interactions to recruit a deaminase in trans. These observations led to the development

of the cis and trans-editing models for RNA editing that posits that the deaminase may be

provided in cis from a single PPR or in trans in PPRs that lack a DYW domain. PPRs, such as MEF8, which have a short RNA binding domain and an intact deaminase domain,were identified as candidates for a trans-deaminases. RNAseq analysis was performed

on mef8 null mutants and catalytically ablated variants to examine the role of MEF8 in

mitochondrial editing. Sixty editing sites were affected, and suggests that MEF8 may

participate as a trans-editing deaminase by providing deaminase capability for a large

number of editing sites.

The role of reactive oxygen species (ROS) during editing dysfunction was investigated to

examine the potential mechanisms of sensing and signaling oxidative distress. LPA66

mutant plants fail to edit a photosystem II polypeptide and exhibit a strong phenotype.

Mutant plants produced elevated levels of ROS, and transcriptomic analysis revealed

higher expression of ROS reactive network genes and PPR or editing related genes.

Lipidomics analysis of the mutant indicated highly elevated levels of oxylipins including

arabidoside A and G and phytoprostanes. Possible signaling mechanisms through

oxylipins and jasmonic acid pathways are discussed.