While automakers lay off staff and shut down plants in response to the economic downturn, one automaker announced Thursday that it will open a manufacturing plant in the United States, potentially creating hundreds of jobs in the area eventually chosen. Tesla Motors, maker of a high-end electric sports car, says it will build an all-electric sedan in Southern California. Thursday’s announcement was made in Hawthorne, California, where Tesla unveiled the Model-S sedan at a base price of $57,400.