Endonuclease which cleaves flap structures at the junction between single-stranded DNA and double-stranded DNA. Possesses both single-stranded and double-stranded DNA-binding activities. Involved in early microspore development, but does not alter meiosis or tapetal cells development (PubMed:15792960, PubMed:22247560). Possesses Holliday junction (HJ) resolvase activity in vitro. Cleaves HJ at symmetrically related sites of the branch point (PubMed:22247560). Binds 2 magnesium ions per subunit. They probably participate in the reaction catalyzed by the enzyme. May bind an additional third magnesium ion after substrate binding. Monomer. Interacts with PCNA. PCNA stimulates the nuclease activity without altering cleavage specificity. Highly expressed in anthers. Expressed in roots and leaves. Plants develop abnormal anthers with degraded microspores, causing male sterility. Belongs to the XPG/RAD2 endonuclease family. GEN subfamily.