Among individual movers, FedEx FDX.N slid 2.9% after the shipping firm reported a decline in quarterly earnings and said global shipping downturn has hurt margins for the sector. By Shubham Batra and Johann M Cherian June 21 (Reuters) - Wall Street's main indexes were set to open lower on Wednesday as Federal Reserve Jerome Powell remained firm in bringing inflation back to 2% target, spurring worries of more monetary tightening. Megacap companies struggled to gain as yields on the 2-year treasury notes, which move in line with interest rate expectations, rose marginally after Powell's comments.