Under Massachusetts' new healthcare cost-control law, legislators are counting on physician assistants like Tuff as critical partners in the effort to curb medical spending, improve the coordination of treatment, and give patients easier access to basic care amid a shortage of primary care doctors. A little-known provision of the law, which Governor Deval Patrick signed in August, expands the role of physician assistants by requiring health plans to list them as primary care providers in directories and allow patients to choose a physician assistant as their provider. They still will work on teams with doctors, but they will have their own group of patients for whom they are primarily responsible. Nurse practitioners were given similar status in a 2008 state law.