Essential protein required during embryogenesis (PubMed:15266054). Key enzyme involved in DNA replication and damage repair, shoot apical meristem (SAM) maintenance, and development (PubMed:26951435). Involved in Okazaki fragments processing. Possesses different enzymatic activities, such as single-stranded DNA (ssDNA)-dependent ATPase, 5'-3' helicase and endonuclease activities. While the ATPase and endonuclease activities are well-defined and play a key role in Okazaki fragments processing and DSB repair, the 5'-3' DNA helicase activity is atypical: it cannot load onto its tracking strand internally and has an absolute free 5'-end requirement (By similarity). ATP + H2O = ADP + H(+) + phosphate Binds 1 [4Fe-4S] cluster. Localized to nuclear foci in response to DNA damage. Strongly expressed in meristems, including both root and shoot apical meristems (RAM and SAM) (PubMed:26951435). Also present in the vasculature and in young floral tissues (PubMed:26951435). Defective embryo arrested at preglobular/early globular stage with the formation of giant endosperm nuclei (PubMed:15266054). In jhs1, retarded growth, abnormal pattern of shoot apical meristem (SAM) cell division and differentiation, and morphological defects such as fasciation, irregular arrangement of siliques and phyllotaxy, and short roots (PubMed:26951435). Increased sensitivity to DNA damage stress (PubMed:26951435). Increased DNA damage response, including increased expression of genes involved in DNA damage repair and cell cycle regulation, and a higher frequency of homologous recombination (PubMed:26951435). Meristems exhibit a delayed cell cycle progression at the G2 or late S phase, and a misregulation of genes essential for meristem maintenance (PubMed:26951435). 'Jing he sheng' means fasciated stem in Chinese. Belongs to the DNA2/NAM7 helicase family.