The companion cells of the Arabidopsis thaliana egg and sperm, the central and vegetative cells, undergo active DNA demethylation prior to fertilization. However, its biological significance, extent of conservation, and targeting preferences are not yet clear. We recently showed that localized demethylation of interspersed, small transposable elements is a common feature of A. thaliana companion cells. The DEMETER DNA glycosylase encodes active DNA demethylase activity and is required for seed production. DME-mediated DNA demethylation in the central cell is required to establish imprinted gene expression in the endosperm, and is considered a master regulator for plant gene imprinting. However, the similarity among DME targets in the central and vegetative cells, despite their different functions and developmental fates, suggests that establishment of genomic imprinting may not be the basal function of DME. Lack of DEMETER in vegetative cells causes reduced methylation of transposons in sperm. Our observation suggests that the primary function of companion cell demethylation is to reinforce transposon silencing in plant gametes.

본 연구는 동해남부해역의 수하식 우렁쉥이 양식장에서 양식되고 있는 2년산 우렁쉥이, Halocynrhia roretzi의 생식세포 및 생식소 발달과 성숙 조사를 위하여 1996년 5월부터 1997년 4월에 걸쳐 조사되었다. 우렁쉥이는 자웅동체형으로 난생이었다. 난소는 체벽에 평행하게 붙어 좌측에 6~8개, 우측에 8~10개의 가는 생식수관을 가진 구조이며, 정소는 난소 사이에 불규칙 한 많은 낭상 구조를 가진 복합 생식소이었다. 난원세포는 직경이 11.