Replication of the plant genome

Abstract

All multicellular organisms, whether plants or animals, have similar requirements and challenges in replicating their genomes. At each cell cycle, the entire genome must be fully and faithfully duplicated, so that identical copies of the genome are delivered to the new daughter cells during mitosis. The first experimental work aimed at elucidating the mechanism of DNA replication was performed in plants and demonstrated unequivocally that DNA and chromosomal replication occurs through a semiconservative mechanism. The greatest difference between the proteins forming the pre-replication complex (pre-RC) in animal and plant cells resides in the cell division cycle10-dependent transcription 1 (CDT1)-interacting proteins in both kingdoms. In animals, CDT1 interacts with geminin, while plants lack a geminin ortholog, and encode a completely unrelated CDT1-interacting protein, GLABRA2 (GL2) EXPRESSION MODULATOR (GEM). Although consensus sequences have not been identified for Arabidopsis replication origins, they tend to be rich in G+C and are similar in their basic characteristics to those of animal cells. Plant replication origins are largely associated with histone H2A.Z and H3.3 variants, as well as with histone modifications characteristic of active transcription. The specific features of several components of the replication machinery are well characterized in plants. This is the case of DNA polymerases, the accessory factors, and the enzymes involved in the maturation of Okazaki fragments. As was first shown in plants, the replication of the genome does not occur randomly but instead is organized temporally into early and late replicating regions. Endoreplication, i.e., genome duplication without mitosis, is frequent in many cell types within the adult plant body. It occurs in all multicellular eukaryotes, being very common and functionally relevant in plants, in which it is necessary for cell growth and differentiation. DNA replication in plants has some specific features mainly derived from the regulation of protein availability, the frequent occurrence of endoreplication, and the response to hormonal, developmental, and environmental cues.