PolA2 is required for embryo development in Arabidopsis

DNA replication machinery is highly conserved in eukaryotes. DNA polymerase is essential for the synthesis of new DNA strands and for DNA repair. Despite the significant progress in the understanding of these processes in yeast and animal model systems, there is only scant information available for their counterparts in plants. Among different multisubunit-containing DNA polymerases, DNA polymerase a (POLA complex) is composed of four subunits. In this study, we report on the characterization of PolA2, which encodes the putative B subunit of DNA polymerase a in Arabidopsis thaliana (L.) Heynh. PolA2 is a single copy gene in Arabidopsis and shows highly conserved regions with putative homologs in other plant species. Insertional inactivation of PolA2 in Arabidopsis leads to embryo lethality, with developmental arrest at or before the four-cell stage during embryogenesis. The apical cell lineage is strongly affected in the mutant embryos and the endosperm initial cell fails to divide. PolA2 is expressed broadly in the early phases of embryo development during the period of active cell divisions, while during the later stages of development expression is reduced and more localized. Ectopic overexpression of PolA2 produced dominant negative phenotypes with gametic and embryo lethality suggesting that coordinated and parallel expression with other subunits is critical for its proper function in DNA replication and plant development.