The tobacco chloroplast gene is essential for transcriptional gene regulation and plants photoautotrophic growth.

A tobacco chloroplast hypothetical open reading frame 4 (YCF4) has been reported as a non-essential assembly factor for photosynthesis based on an incomplete knockout of YCF4, just 93 of 184 amino acids from the N-terminus were knocked out. On the other hand, we removed the complete sequence of from tobacco chloroplasts and observed that Δ plants were unable to survive photoautotrophically as their growth was hampered in the absence of an external carbon supply, clearly showing that the YCF4 is essential for photosynthesis. Initially, the gene was introduced into the tobacco plastome replacing the complete gene through homologous recombination events.