“…Distinct from the other GUN genes, GUN1 is the only known GUN gene that, when defective, results in derepression of the expression of PhANGs in the presence of both Lin (which inhibits PGE by blocking chloroplast translation) and NF (which affects TPB signaling; Koussevitzky et al, 2007;Wu et al, 2018Wu et al, , 2019. Interestingly, the GUN1 mutation was shown to restore PhANG expression in plastid sigma factor mutants (Woodson et al, 2013), the prors1 mutant (defective in prolyl-tRNA synthetase in both chloroplasts and mitochondria; Tadini et al, 2016), and the prin2 mutant (affecting a locus required for full expression of genes transcribed by the plastid-encoded RNA polymerase; Kindgren et al, 2012a;Díaz et al, 2018). Together, these findings indicate a central role of GUN1 in the PGE pathway of retrograde signaling.…”