Chloroplastencoded

Chloroplastencoded refers to genes that are encoded within the chloroplast genome, the circular DNA molecule contained in chloroplasts. These genes are distinct from nuclear genes, even though many chloroplast proteins are synthesized in the cytosol and imported into chloroplasts.

In most land plants, the chloroplast genome is about 120,000 to 160,000 base pairs and carries roughly 110 to 130 genes. The gene set includes components of photosystems I and II, the chloroplast ATP synthase, and the cytochrome b6f complex, as well as the RNA polymerase subunits and ribosomal RNAs and proteins needed for chloroplast translation. Many chloroplast genes are arranged in operon-like clusters and, in higher plants, the genome often features a quadripartite structure with large and small single-copy regions separated by inverted repeats. Some genes contain introns, such as matK and certain tRNA genes.

Chloroplast genes are expressed by a combination of plastid-encoded and nucleus-encoded factors. Transcription uses plastid RNA polymerases, including a bacteria-like plastid-encoded polymerase and a nucleus-encoded polymerase, while translation relies on chloroplast ribosomes (70S) and a small set of tRNAs. The expression and regulation of chloroplastencoded genes are integrated with nuclear gene networks that control chloroplast development and function.

Evolutionarily, chloroplasts originated from cyanobacteria through endosymbiosis. Over time, many genes have relocated to the nuclear genome, but chloroplastencoded genes remain essential for photosynthesis and plastid gene expression. The term is commonly used in contrast to nuclear-encoded, chloroplast-targeted proteins and in studies of chloroplast evolution, phylogeny, and biotechnology.