Here's what you need to know before the markets open. 1. Global stocks tank after Apple warns Wuhan coronavirus is hammering sales. The news sent the tech titan's shares down 3.5% in pre-market trading, wiping $50 billion off its market capitalization. 2. A famous hedge fund bought Tesla stock before it surged 91% this year. Renaissance Technologies had a 2.1% stake in Elon Musk's startup worth $1.6 billion at the end of December. 3. Apple's coronavirus warning that it won't sell enough iPhones is great news for Samsung.