Functional characterisation of PPR-SMR proteins in Arabidopsis thaliana

Sheng Liu

Research output: ThesisDoctoral Thesis

358 Downloads (Pure)

Abstract

PPR (pentatricopeptide repeat) proteins are characterised by tandem repeats of a
degenerate 35 amino acid motif, most of which have roles in RNA metabolism within
mitochondria and/or chloroplasts. The Arabidopsis thaliana genome contains a small
sub-family of eight PPR proteins characterised by their C-terminal small MutS-related
(SMR) domain. Four of the PPR-SMR proteins that localise to the chloroplast, namely
GUN1, PTAC2, SOT1 and SVR7, were characterised by in silico analyses and
experimental approaches. Phylogenetic analysis shows that PPR-SMR proteins are
ancient, being present in single-cell algae as well as land plants. GUN1 has been at the
centre of chloroplast retrograde signalling research for many years, but mutants
lacking the similar SOT1 or SVR7 proteins do not show a gun phenotype, suggesting
that although their molecular functions are likely to be similar, their physiological roles
are different. The most notable discovery is that SOT1 is required for the correct
processing of the 5’ end of the 23S-4.5S precursor, playing an important role in 23S
rRNA biogenesis. This is consistent with a potential binding site for SOT1, predicted
using the PPR “code”, at the 5' extremity of the 23S-4.5S rRNA precursor. The
functions of the PPR tracts and SMR domains within SOT1 and SVR7 were
investigated by expressing truncated forms of the proteins and by domain swaps
between the proteins. Their PPR domains are absolutely required for function and
determine their specificity of action, but the requirement for their SMR domains differ.
Original languageEnglish
QualificationDoctor of Philosophy
Supervisors/Advisors
  • Howell, Kate, Supervisor
  • Small, Ian, Supervisor
  • Whelan, James, Supervisor
Publication statusUnpublished - 2016

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