The GENOMES UNCOUPLED1 protein has an ancient, highly conserved role but not in retrograde signalling

The pentatricopeptide repeat protein GENOMES UNCOUPLED1 (GUN1) is required
for chloroplast-to-nucleus signalling in response to plastid stress during
chloroplast development in Arabidopsis thaliana but its
exact molecular function remains unknown. Current data on GUN1 function is
limited to Arabidopsis, so we set out to investigate the origin
and evolution of the land plant GUN1 proteins. We retrieved GUN1 sequences
from 76 phylogenetically diverse land plants and developed a GUN1 sequence
profile using hmmbuild (http://hmmer.org). We then used this
profile to systematically analyse the presence/absence of GUN1 sequences
in transcriptomes from land plants and streptophyte algae. This dataset
includes the GUN1 profile we developed, the code we used to analyse the
results of screening over 500,000 PPR protein sequences with the profile,
and an alignment of the 893 GUN1 sequences that we obtained. We used this
data to show that GUN1 is an ancient protein that is highly conserved
across land plants but missing from
the Rafflesiaceae that lack chloroplast genomes. Our
findings suggest that GUN1 is an ancient protein that evolved within the
streptophyte algal ancestors of land plants before the first plants
colonised land more than 470 million years ago. 
This dataset also includes transcript count data from an RNA-seq
experiment looking at gene expression in liverwort Marchantia
polymorpha wild type and Mpgun1 mutant spore
samples grown in the presence or absence of spectinomycin. We used this
data to show that GUN1 does not act significantly in chloroplast
retrograde signalling in the liverwort M. polymorpha. Its primary
role is likely to be in chloroplast gene expression and its role in
chloroplast retrograde signalling probably evolved more recently.