We investigate a nonconvex, nonsmooth optimization approach based on DC (Difference of Convex functions) programming and DCA (DC Algorithm) for the reduced-rank multitask linear regression problem with covariance estimation. The objective is to model the linear relationship between a multitask response and more explanatory variables by estimating a low-rank coefficient matrix and a covariance matrix. The problem is formulated as minimizing the constrained negative log-likelihood function of these two matrix variables. Then, we consider a reformulation of this problem which takes the form of a partial DC program i.e. it is a standard DC program for each variable when fixing the other variable. Next, an alternating version of a standard DCA scheme is developed. Numerical results on many synthetic multitask linear regression datasets and benchmark real datasets show the efficiency of our approach in comparison with the existing alternating/joint methods.