The chloroplast genomes of most higher plants contain two giant open reading frames designated ycf1 and ycf2. Although the function of Ycf1 is unknown, it is known to be an essential gene [1].

1: The two largest chloroplast genome-encoded open reading frames of higher plants are essential genes. Drescher A, Ruf S, Calsa T Jr, Carrer H, Bock R; Plant J 2000;22:97-104. PMID:10792825