  In this paper we commence the study of discrete harmonic analysis associated
with Jacobi orthogonal polynomials of order $(\alpha,\beta)$. Particularly, we
give the solution $W^{(\alpha,\beta)}_t$, $t\ge 0$, and some properties of the
heat equation related to the operator $J^{(\alpha,\beta)}-I$, where
$J^{(\alpha,\beta)}$ is the three-term recurrence relation for the normalized
Jacobi polynomials and $I$ is the identity operator. These results will be a
consequence of a much more general theorem concerning the solution of the heat
equation for Jacobi matrices. In addition, we also prove the positivity of the
operator $W^{(\alpha,\beta)}_t$ under some suitable restrictions on the
parameters $\alpha$ and $\beta$. Finally, we investigate mapping properties of
the maximal operators defined by the heat and Poisson semigroups in weighted
$\ell^{p}$-spaces using discrete vector-valued local Calder\'{o}n-Zygmund
theory. For the Poisson semigroup, these properties follows readily from the
control in terms of the heat one.
