Plastidencoded

Plastidencoded refers to genes located in the genome of plastids, the plant and algal organelles that carry out photosynthesis. In most lineages plastids contain a circular DNA molecule, the plastome, which is inherited maternally in many plants and typically encodes a subset of the organism’s genes. Over evolutionary time, many plastid genes have been transferred to the nuclear genome, with their protein products imported back into plastids; thus plastid-encoded genes represent a reduced but essential set of functions within the organelle.

Typical plastid-encoded genes encode components of the transcription and translation machinery (rRNA, tRNA, ribosomal proteins, and the plastid-encoded RNA polymerase subunits rpoA, rpoB, rpoC1, rpoC2), as well as core photosynthetic complexes (photosystem I and II subunits encoded in psa and psb, cytochrome b6/f Pet genes), ATP synthase subunits (atp genes), and other housekeeping functions. The content is relatively conserved across diverse groups, though some lineages have lost several ndh genes or other functions.

Expression of plastid genes is carried out by two RNA polymerases: a plastid-encoded bacterial-type PEP and a nucleus-encoded NEP that transcribes many housekeeping genes. Plastid gene products are translated on plastid ribosomes and are often involved in photosynthesis, plastid gene expression, and metabolism. The matK gene, encoding a maturase, is widely used in studying intron splicing and is a common component of plastome analyses.

Because plastid genomes are compact and relatively conserved, plastid-encoded sequences are valuable for phylogenetics, barcoding, and biotechnological applications, including engineering of plastid genomes (plastid transformation) for trait expression.