Fannie Mae is testing the market for single-family rental homes by backing a large institutional investor for the first time. In an agreement to fund up to $1 billion of collateral owned by Invitation Homes, Fannie, along with Wells Fargo Bank, issued a commitment letter to the Dallas-based company. Invitation, a subsidiary of Blackstone, is the largest single-family rental operation, with a portfolio of close to 50,000 homes that it acquired from foreclosure auctions to fix up and rent.The commitment states that the GSE will be involved in a “securitization transaction” with the SFR operator “to fund a new 10-year fixed rate mortgage loan in a...