Originally spotted by Guru3D.com, both new motherboards are most likely based on AMD's B350 chipset although it could also be the entry-level A320. Due to further integration with AMD's upcoming AM4 chips, the southbridge, also known as the FCH, will only add further PCIe lanes and additional SATA and USB ports.
The first pictured motherboard from Gigabyte is based on the micro-ATX form-factor and has a single PCI-Express 3.0 x16 slot, two DDR4-DIMM slots and four SATA 6Gbps ports. It also features standard 5.1-channel audio, Gigabit Ethernet and up to 6 USB 3.0 ports.
The second one is a bit more interesting and appears to be a version of the motherboard that was spotted earlier in September with two PCI-Express 3.0 x16 slots (one limited to electrical x4), has six SATA 6Gbps ports, M.2 slot and few more USB 3.0 ports.
AMD's entry-level A320 and mid-range B350 will be targeting AMD's 7th generation Bristol Ridge APUs but also support AMD's upcoming Zen-based Summit Ridge CPUs, more suitable for AMD's high-end X370 chipset.