Shares of Roku plunged more than 8 percent Wednesday after Amazon and Best Buy announced plans to team up to sell smart TVs.

Under the deal, Best Buy will become one of the only brick-and-mortar retailers where customers can walk in and buy a TV powered by Amazon's Fire TV software. The TVs will also be sold on Best Buy's website. In exchange, Best Buy will be a third-party seller on Amazon.com, giving the retailer access to Amazon's vast customer network.