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. The South Korean electronics giant, which makes half of its smartphones in Vietnam, feels "relieved," a source told Reuters.4. China will grant tariff exemptions on additional US goods. Chinese officials said they would exempt US imports such as pork, soybeans, and crude oil from tariffs.5. SoftBank spends $2.5 billion to get its second Vision Fund off the ground. The Japanese tech titan has pumped its own cash into new investments since October, people familiar with the matter told Reuters.6. Walmart's holiday sales hurt by shorter season, lower demand for apparel. The retail titan's same-store US sales rose 1.9% excluding fuel, undershooting analysts' forecast of a 2.4% rise.7. If Apple is hurting due to the coronavirus, its suppliers and rivals likely are too. The tech titan's revenue warning might signal trouble for makers of microchips and other components, and rivals who build their products in China.8. Stocks are plunging. In Europe, Germany's DAX slid 0.8%, Britain's FTSE 100 dropped 1%, and the Euro Stoxx 50 slumped 0.6%. In Asia, China's Shanghai Composite was almost flat, Hong Kong's Hang Seng tumbled 1.5%, and Japan's Nikkei fell 1.4%. US stocks are set to open lower with futures underlying the Dow Jones Industrial Average and S&P 500 down 0.5% to 0.6%, and Nasdaq futures down 0.8%.9. Earnings season continues. Walmart's fourth-quarter earnings are the highlight.10. Fresh data is on the way. Housing and New York State manufacturing figures are coming out.Join the conversation about this storyNOW WATCH: A big-money investor in juggernauts like Facebook and Netflix breaks down the '3rd wave' firms that are leading the next round of tech disruption Click here to read full news..