Effects of inefficient transcription termination of rbcL on the expression of accD in plastids of Arabidopsis thaliana.

The plastid accD gene encodes one subunit of a multimeric acetyl-CoA carboxylase that is required for fatty acid biosynthesis. In Arabidopsis thaliana, the accD gene is transcribed by the nuclear-encoded phage-type RNA polymerase, and the accumulation of accD transcripts is subjected to a dynamic pattern during chloroplast development. However, the mechanisms underlying the regulation of accD expression remain unknown. Here, we showed that the inefficient transcription termination of rbcL due to the absence of RHON1 impaired the developmental profile of accD, resulting in the constitutive expression of accD during chloroplast development. Moreover, the accumulation of accD transcripts accordingly resulted in an increase in accD protein levels, suggesting that transcript abundance is critical for accD gene production. Our study demonstrates that the interplay between accD and upstream rbcL regulates the expression of accD and highlights the significance of transcriptional regulation in plastid gene expression in higher plants.