A role of GUNs-Involved retrograde signaling in regulating Acetyl-CoA carboxylase 2 in Arabidopsis.

In Arabidopsis thaliana (Arabidopsis), Acetyl-CoA Carboxylase 2 (ACC2) is a nuclear DNA-encoded and plastid-targeted enzyme that catalyzes the conversion of acetyl-CoA to malonyl-CoA. ACC2 improves plant growth and development when chloroplast translation is impaired. However, little is known about the upstream signals that regulate ACC2. Here, through analyzing the transcriptome changes in brz-insensitive-pale green (bpg) 2-2, a pale-green mutant with impaired chloroplast gene expression resulting from loss of the BPG2 function, we found that the level of ACC2 was significantly up-regulated. Through performing genetic analysis, we further demonstrated that loss of the GENOMES UNCOUPLED 1 (GUN1) or GUN5 function partly perturbed the up-regulation of ACC2 in the bpg2-2 mutant, whereas ABA INSENSITIVE 4 (ABI4)-function-loss had no clear effect on the ACC2 expression. Furthermore, when plants were treated with plastid translation inhibitors, such as lincomycin and spectinomycin, the ACC2 transcriptional level was also markedly increased in a GUN-dependent manner. In conclusion, our results suggested that the GUN-involved plastid-to-nucleus retrograde communication played a role in regulating ACC2 in Arabidopsis.