The Ubuntu MATE Developers utilize a MATE 1.8.1 PPA Repo ported from Debian for use with the Trusty (14.04) Ubuntu MATE Remix.
sudo apt-add-repository ppa:ubuntu-mate-dev/ppa
sudo apt-add-repository ppa:ubuntu-mate-dev/trusty-mate
Install MATE 1.8.1
First make sure your package list and packages are up-to-date by running:
sudo apt-get update
sudo apt-get upgrade
You can choose to install Vanilla MATE by picking one of the apt-get options below.
This will install the base packages required for a minimal MATE desktop
sudo apt-get install mate-desktop-environment-core
This will install the complete MATE desktop
sudo apt-get install mate-desktop-environment
This will install the complete MATE desktop including a few extras (Most Users Will Want This)
sudo apt-get install mate-desktop-environment-extras
Alternatively you may choose to install Ubuntu MATE Remix.
Ubuntu MATE is a more comprehensive option that offers a slightly tweaked layout, configuration, and themes to integrate into Ubuntu in a more seamless fashion. This will install the complete MATE Desktop Environment as well as LightDM and numerous other applications to provide a full and well rounded desktop.
sudo apt-get install ubuntu-mate-core ubuntu-mate-desktop