Genetic algorithm and nonlinear constraints

I want to minimize a simple fitness function of four variables x1,x2,x3,x4,x5 and x6 such that the following nonlinear constraints are satisfied if x1 > 2000, then x4>1.5 if x2 > 2500, then x5>2.0 if x3 > 3000, then x4>2.5 but i dont know how to write these constraints into the matlab.