It appears that the software package GUI installer, gpk-application, 
does not have what is needed for an install of MATE
under SL.  (One evidently does not need MATE for SL 6 as Gnome 2 is part 
of the stock SL 6 distribution).  During the base install of SL 7,
I always install both whatever Gnome and KDE GUIs are supplied; thus the 
comment below about X windows is not relevant for my use.
I do this on servers as well as workstations so that graphical machine 
"workload" display and analysis tools are available in addition to the
scrolling text tools.  (Sometimes a visualisation provides insight that 
a table or text does not.)

From:

http://wiki.mate-desktop.org/download

Red Hat Enterprise Linux 7

MATE is available through the Extra Packages for Enterprise Linux (EPEL) 
repository, maintained by the Fedora Project. This should work on CentOS 
7 as well, and any other compatible derivatives.

After you install the epel-release-7*.rpm package to add the EPEL 
repository to Yum, you can install MATE with the following command:

yum groupinstall mate-desktop
If you install this on a minimal system without an existing GUI 
configured (such as a GNOME or KDE desktop), you might want to install 
the X Window System group as well for local graphical logins:

yum groupinstall "X Window System"
you may also want to change the default systemd target to graphical:

systemctl set-default graphical.target

End quote.  Note that unlike other entries in this URL document, the 
actual release (version) of MATE is not given (presumably because the 
document maintainers do not have the time or perhaps do
not get information from the EPEL "team",  Also, unlike the entry for 
Debian that states:
Debian

MATE 1.8.1 is currently packaged for Debian 8 (jessie). MATE 1.12 is 
also available on Debian testing (“Stretch”) and unstable (“Sid”).

(If sudo is unavailable on your system, simply omit it and use a root 
shell)
First make sure your package list is up-to-date by running:

sudo apt-get update
To install MATE, choose 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
sudo apt-get install mate-desktop-environment-extras

End quote

There is no explanation of just which components are automagically 
loaded through the use of the RHEL 7 instructions; that is,
there is no explicit equivalent of:   This will install the complete 
MATE desktop including a few extras
sudo apt-get install mate-desktop-environment-extras

i am not certain what are in the "extras"; I do know that after I got 
MATE up and running on my wife's SL7.2 laptop, I had to hunt for the 
other RPMs I needed
to get MATE GUI displays of what she expected (and I also use on  my 
MATE desktop).  I am referring to items for the MATE menu and items for 
a MATE panel (e.g.,
applets).

Yasha Karant
;