As you may know, Ubuntu MATE is the newest member of the Ubuntu family, created to catch and hold the GNOME2 fans.
The latest version available is MATE 1.12.1, which has been recently released, bringing hotfixes only. Recently, Martin Wimpress, the main MATE developer, has announced that MATE 1.12.1 will be added to the default repositories of Debian Unstable and Ubuntu MATE 16.04 Alpha 1.
As a reminder, all the official flavors of Ubuntu 16.04 (except Ubuntu Unity) will be released today in the first beta version.