WASHINGTON (Reuters) - A Republican senator who has publicly opposed the current draft of the Senate tax reform plan said on Thursday he wants to see more tax relief for pass-through businesses, like partnerships, because he sees them as the source of U.S. economic growth. “I want more of the tax relief on the business side to flow to pass-through industries because I really do believe they are the true engine of economic growth and job creation,” Senator Ron Johnson told CNN, but gave no details about specific fixes. Johnson later told CNBC that despite his opposition to the current draft, he was optimistic Republicans can pass a tax reform plan this year.    