Intel socket LGA1150 CPUs have an embedded memory controller, meaning that it is the processor, not the chipset, that defines what memory technologies you can have and the maximum amount of memory that is possible. The motherboard, however, may have a limitation as to how much memory can be installed.
The integrated memory controller from socket LGA1150 processors supports DDR3 memories up to 1,600 MHz. According to ASUS, the Z97-PRO supports memories up to 3,200 MHz.
The ASUS Z97-PRO has four memory sockets. You can install up to 32 GiB with this motherboard if you use four 8 GiB modules.
In order to enable the dual-channel mode, you must install two or four memory modules. On this motherboard, the first and third memory sockets are black, while the second and fourth are dark gray. When installing two memory modules, use two sockets with the same color.