Bifunctional DNA glycosylase/lyase, which excises 5-methylcytosine (5-meC) and 5-hydroxymethylcytosine (5-hmeC), leaving an apyrimidinic (AP) site that is subsequently incised by the lyase activity (Probable). DNA demethylase that is indispensable in both male and female gametophyte development (PubMed:22448681). Involved in the regulation of DNA methylation in the promoters of RISBZ1/BZIP58 and DOF3/RPBF, two transcription factors that functions synergistically to positively regulate genes that are key players in the development of aleurone layers (PubMed:30275307). Active DNA demethylation carried out by ROS1A in rice endosperms may restrict the number of aleurone cell layers (PubMed:30275307). Binds 1 [4Fe-4S] cluster. The cluster does not appear to play a role in catalysis, but is probably involved in the proper positioning of the enzyme along the DNA strand. Expressed in roots, leaf blades, leaf sheaths, apical and lateral shoot meristems, inflorescence meristems, lodicules, pollen grains, ovules and seeds (PubMed:22448681). Expressed in vascular tissues of roots and leaves, pollen grains, pericarp, aleurone, and starchy endosperm (PubMed:30275307). Sterility and inability to set normal seeds due to severe defects in both male and female gametogenesis. Reducing ROS1A activity may be a potential tool to increase aleurone content, and improve the nutritional value of rice grains (PubMed:30275307). Aleurone cells are rich in an array of proteins, vitamins and minerals (PubMed:30275307). Belongs to the DNA glycosylase family. DEMETER subfamily.