BAGHDAD, Jan 24 (Reuters) - Gunmen opened fire on the motorcade of Iraq's higher education minister on a highway in southern Baghdad on Wednesday, killing one of his guards, the minister told Reuters. "We were exposed to gunfire at different points along the highway. One of my guards was killed and another was shot in the head and seriously wounded," Higher Education Minister Abd Dhiab al-Ajili, a Sunni, said.