An AP Endonuclease Functions in Active DNA Dimethylation and Gene Imprinting in Arabidopsis

Active dna demethylation in plants occurs through base excision repair,beginning with removal of methylated cytosine by the ros1/dme subfamily of 5-methylcytosine dna glycosylases. active dna demethylation in animals requires the dna glycosylase tdg or mbd4,which functions after oxidation or deamination of 5-methylcytosine,respectively. however,little is known about the steps following dna glycosylase action in the active dna demethylation pathways in plants and animals. we show here that the arabidopsis ape1l protein has apurinic/apyrimidinic endonuclease activities and functions downstream of ros1 and dme. ape1l and ros1 interact in vitro and co-localize in vivo. whole genome bisulfite sequencing of ape1l mutant plants revealed widespread alterations in dna methylation. we show that the ape1l/zdp double mutant displays embryonic lethality. notably,the ape1l+/−zdp−/− mutant shows a maternal-effect lethality phenotype. ape1l and the dna phosphatase zdp are required for fwa and mea gene imprinting in the endosperm and are important for seed development. thus,ape1l is a new component of the active dna demethylation pathway and,together with zdp,regulates gene imprinting in arabidopsis. © 2015 li et al.