Essential protein. DNA ligase that seals nicks in double-stranded DNA during DNA replication, DNA recombination and DNA repair. Involved in repair of both single strand breaks (SSBs) and double strand breaks (DSBs). Required in the endosperm for embryogenesis, probably to repair DNA-breaks generated by DME. ATP + (deoxyribonucleotide)n-3'-hydroxyl + 5'-phospho-(deoxyribonucleotide)m = (deoxyribonucleotide)n+m + AMP + diphosphate. Expressed in all vegetative and reproductive tissues. In the mature male gametophyte, expressed in the vegetative cell as well as in the two sperm cells. In the mature female gametes, accumulates in the embryo sac; mostly expressed in the central cell nucleus and, at lower levels, in the egg cell and synergids. After fertilization, localized in the syncytial endosperm and in the embryo. Lethal. Belongs to the ATP-dependent DNA ligase family. Truncated N-terminus.