Extranuclear DNA and its use in systematics

Abstract

Higher plant cells contain three genetic compartments which separately transcribe DNA and translate messenger (m)RNA into polypeptides. Most plant proteins derive from nuclear genes and their mRNAs are translated on ribosomes in the cytoplasm. Many fewer genes are located within mitochondrial (mt) or plastid (including chloroplast (cp)) DNA, and mRNAs from these genomes are translated on separate populations of ribosomes within the particular organelles. The cytoplasmic genomes are much smaller than that of the nucleus and they are present in multiple copies in each organelle. As there are many chloroplasts and mitochondria in each cell, these genomes may contribute a large proportion of total cellular DNA. Chloroplast DNA, in particular, has been extensively used to study plant phylogeny. The reasons why it is useful and some of the possible problems associated with its use in taxonomy are discussed.