Selectman Tiziano Doto is a candidate in the race for Southern Middlesex Register of Deeds. Doto, a Democrat, last month filed with the secretary of state’s office the certified signatures he needed to earn a spot on the September primary ballot. Five other candidates, all Democrats, are competing for the seat, which is open because Democratic incumbent Eugene Brune of Somerville is not seeking another term. Registers of deeds are responsible for maintaining county land records. Doto has practiced law in Somerville and Stoneham since 1993, specializing in commercial and residential real estate and title transactions. He is also a licensed real estate broker. A first-term selectman, he is currently the board’s vice chairman and chairs its collective bargaining committee. He has also served on the Zoning Board of Appeals.